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What Is a Cladogram? Definition and Examples

What a Cladogram Is (and Isn’t)

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Ornithischian Dinosaur Cladogram
Tinkivinki / Getty Images


By Anne Marie Helmenstine, Ph.D.Updated on January 10, 2020

cladogram is a diagram that represents a hypothetical relationship between groups of organisms, including their common ancestors. The term “cladogram” comes from the Greek words clados, which means “branch,” and gramma, which means “character.” The diagram resembles the branches of a tree that extend outward from a trunk. However, the shape of the cladogram isn’t necessarily vertical. The diagram can branch from the side, top, bottom, or center. Cladograms can be very simple, comparing only a few groups of organisms, or highly complex, potentially classifying all forms of life. However, cladograms are more often used to classify animals than other forms of life.https://e2586ea16521ee392ccb4632d7959afb.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Scientists use synapomorphies to compare groups to construct a cladogram. Synapomorphies are shared common heritable characteristics, such as having fur, producing shelled eggs, or being warm-blooded. Originally, synapomorphies were observable morphological traits, but modern cladograms use DNA and RNA sequencing data and proteins.https://e2586ea16521ee392ccb4632d7959afb.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

The method of hypothesizing relationships between organisms and constructing cladograms is called cladistics. The hypothetical relationships between organisms is called a phylogeny. The study of the evolutionary history and relationships between organisms or groups is called phylogenetics.

Key Takeaways: What Is a Cladogram?

  • A cladogram is a type of diagram that shows hypothetical relationships between groups of organisms.
  • A cladogram resembles a tree, with branches off a main trunk.
  • Key aspects of a cladogram are the root, clades, and nodes. The root is initial ancestor that is common to all groups branching off from it. The clades are the branches that indicate related groups and their common ancestors. Nodes are the points that indicate the hypothetical ancestors.
  • Originally, cladograms were organized based on morphological features, but modern cladograms are more often based on genetic and molecular data.

Parts of a Cladogram

The root is the central trunk of a cladogram that indicates the ancestor common to all groups branching from it. A cladogram uses branching lines that end in a clade, which is a group of organisms sharing a common hypothetical ancestor. The points where the lines intersect are the common ancestors and are called nodes.https://e2586ea16521ee392ccb4632d7959afb.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Two identical cladograms
 These are two identical cladograms. Alexei Kouprianov / Creative Commons Attribution-Share Alike 3.0

Cladogram vs. Phylogram

A cladogram is one of several types of tree diagrams used in phylogenetics. Other diagrams include phylograms and dendrograms. Some people use the names interchangeably, but biologists recognize distinct difference between the tree diagrams.

Cladograms indicate common ancestry, but they do not indicate the amount of evolutionary time between an ancestor and a descendant group. While the lines of a cladogram may be different lengths, these lengths have no meaning. In contrast, the branch lengths of a phylogram are proportional with respect to evolutionary time. So, a long branch indicates a longer time than a shorter branch.https://e2586ea16521ee392ccb4632d7959afb.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Unrooted phylogenetic tree of life.
 This is an unrooted phylogenetic tree of life. zmeel / Getty Images

While they may appear similar, cladograms also differ from dendrograms. Cladograms represent hypothetical evolutionary differences between groups of organisms, while dedrograms represent both taxonomic and evolutionary relationships.https://e2586ea16521ee392ccb4632d7959afb.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

How to Construct a Cladogram

Cladograms are based on comparing similarities and differences between groups of organisms. So, a cladogram could be constructed to describe relationships between different types of animals, but not between individuals. Follow these simple steps to construct a cladogram:

  1. Identify separate groups. For example, the groups could be cats, dogs, birds, reptiles, and fish.
  2. Make a list or table of characteristics. Only list characteristics that can be inherited and not those that are influenced by environmental or other factors. Examples include vertebrae, hair/fur, feathers, egg shells, four limbs. Continue listing traits until you have one trait common to all groups and enough differences between other groups to make a diagram.
  3. It’s helpful to group organisms before drawing the cladogram. A Venn diagram is useful because it shows sets, but you can simply list groups. For example; Cats and dogs both are vertebrates with fur, four limbs, and amniotic eggs. Birds and reptiles are vertebrates that lay shelled eggs and have four limbs. Fish are vertebrates that have eggs, but lack four limbs.
  4. Draw the cladogram. The shared common trait is the root. All of the animals in the example are vertebrates. The first node leads to the branch of organisms with the least in common with the other groups (fish). The next node off the trunk leads to another node that branches off to reptiles and birds. The final node off the trunk branches to cats and dogs. You may be wondering how to decide whether the second node leads to reptiles/birds or to cats/dogs. The reason reptiles/birds follow fish is that they lay eggs. The cladogram hypothesizes the transition from shelled eggs to amniotic eggs occurred during evolution. Sometimes a hypothesis may be incorrect, which is why modern cladograms are based on genetics rather than morphology.

What Is Coevolution? Definition and Examples

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hoverfly and flower
 A hoverfly perched on a flower.Alexander Maack / Getty Images


By Regina BaileyUpdated on June 02, 2019

Coevolution refers to evolution that occurs among interdependent species as a result of specific interactions. That is, adaptations occurring in one species spur reciprocal adaptations in another species or multiple species. Coevolutionary processes are important in ecosystems as these types of interactions shape relationships among organisms at various trophic levels in communities.

Key Takeaways

  • Coevolution involves reciprocal adaptive changes that occur among interdependent species.
  • Antagonistic relationships, mutualistic relationships, and commensalistic relationships in communities promote coevolution.
  • Coevolutionary antagonistic interactions are observed in predator-prey and host-parasite relationships.
  • Coevolutionary mutualistic interactions involve the development of mutually beneficial relationships between species.
  • Coevolutionary commensalistic interactions include relationships where one species benefits while the other is not harmed. Batesian mimicry is one such example.

While Darwin described coevolution processes in plant-pollinator relationships in 1859, Paul Ehrlich and Peter Raven are credited as the first to introduce the term “coevolution” in their 1964 paper Butterflies and Plants: A Study in Coevolution. In this study, Ehrlich and Raven proposed that plants produce noxious chemicals to prevent insects from eating their leaves, while certain butterfly species developed adaptations that allowed them to neutralize the toxins and feed on the plants. In this relationship, an evolutionary arms race was occurring in which each species was applying selective evolutionary pressure on the other that influenced adaptations in both species.https://c0d1eebf6508c3d81c390900b2a3bf19.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Community Ecology

Interactions among biological organisms in ecosystems or biomes determine the types of communities in specific habitats. The food chains and food webs that develop in a community help to drive coevolution among species. As species compete for resources in an environment, they experience natural selection and the pressure to adapt to survive.

Several types of symbiotic relationships in communities promote coevolution in ecosystems. These relationships include antagonistic relationships, mutualistic relationships, and commensalistic relationships. In antagonistic relationships, organisms compete for survival in an environment. Examples include predator-prey relationships and parasite-host relationships. In mutualistic coevolutionary interactions, both species develop adaptations for the benefit of both organisms. In commensalistic interactions, one species benefits from the relationship while the other is not harmed.

Antagonist Interactions

female leopard
 Female leopard stalking prey in tall grass. Eastcott Momatiuk/The Image Bank/Getty Images Plus

Coevolutionary antagonistic interactions are observed in predator-prey and host-parasite relationships. In predator-prey relationships, prey develop adaptations to avoid predators and predators acquire additional adaptations in turn. For example, predators that ambush their prey have color adaptations that help them to blend into their environment. They also have heightened senses of smell and vision to accurately locate their prey. Prey that evolve to develop heightened visual senses or the ability to detect small changes in air flow are more likely to spot predators and avoid their ambush attempt. Both predator and prey must continue to adapt to improve their chances for survival.

In host-parasite coevolutionary relationships, a parasite develops adaptations to overcome a host’s defenses. In turn, the host develops new defenses to overcome the parasite. An example of this type of relationship is evidenced in the relationship between Australian rabbit populations and the myxoma virus. This virus was used in an attempt to control the rabbit population in Australia in the 1950s. Initially, the virus was highly effective in destroying rabbits. Over time, the wild rabbit population experienced genetic changes and developed resistance to the virus. The lethality of the virus changed from high, to low, to intermediate. These changes are thought to reflect the coevolutionary changes between the virus and rabbit population.

Mutualistic Interactions

fig wasps and figs
 The coevolution between fig wasps and figs has become so profound that neither organism can exist without the other. Encyclopaedia Britannica/UIG/Getty Images Plus

Coevolutionary mutualistic interactions that occur between species involve the development of mutually beneficial relationships. These relationships may be exclusive or general in nature. The relationship between plants and animal pollinators is an example of a general mutualistic relationship. The animals depend on the plants for food and the plants depend on the animals for pollination or seed dispersal.

The relationship between the fig wasp and the fig tree is an example of an exclusive coevolutionary mutualistic relationship. Female wasps of the family Agaonidae lay their eggs in some of the flowers of specific fig trees. These wasps disperse pollen as they travel from flower to flower. Each species of fig tree is usually pollinated by a single wasp species that only reproduces and feeds from a specific species of fig tree. The wasp-fig relationship is so intertwined that each depends exclusively on the other for survival.


Mocker Swallowtail
 Mocker Swallowtail.  AYImages/iStock/Getty Images Plus

Coevolutionary commensalistic interactions include relationships where one species benefits while the other is not harmed. An example of this type of relationship is Batesian mimicry. In Batesian mimicry, one species mimics the characteristic of another species for protective purposes. The species that is being mimicked is poisonous or harmful to potential predators and thus mimicking its characteristics provides protection for the otherwise harmless species. For example, scarlet snakes and milk snakes have evolved to have similar coloration and banding as venomous coral snakes. Additionally, mocker swallowtail (Papilio dardanus) species of butterfly mimic the appearance of butterfly species from the Nymphalidae family that eat plants containing noxious chemicals. These chemicals make the butterflies undesirable for predators. Mimicry of Nymphalidae butterflies protects Papilio dardanus species from predators that can not differentiate between the species.  

Scientific Method

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Steps of the scientific method
Illustration by J.R. Bee. ThoughtCo. 


By Regina BaileyUpdated on August 21, 2019

The scientific method is a series of steps followed by scientific investigators to answer specific questions about the natural world. It involves making observations, formulating a hypothesis, and conducting scientific experiments. Scientific inquiry starts with an observation followed by the formulation of a question about what has been observed. The steps of the scientific method are as follows:

  • Observation
  • Question
  • Hypothesis
  • Experiment
  • Results
  • Conclusion


The first step of the scientific method involves making an observation about something that interests you. This is very important if you are doing a science project because you want your project to be focused on something that will hold your attention. Your observation can be on anything from plant movement to animal behavior, as long as it is something you really want to know more about.​ This is where you come up with the idea for your science project.


Once you’ve made your observation, you must formulate a question about what you have observed. Your question should tell what it is that you are trying to discover or accomplish in your experiment. When stating your question you should be as specific as possible.​ For example, if you are doing a project on plants, you may want to know how plants interact with microbes. Your question may be: Do plant spices inhibit bacterial growth?


The hypothesis is a key component of the scientific process. A hypothesis is an idea that is suggested as an explanation for a natural event, a particular experience, or a specific condition that can be tested through definable experimentation. It states the purpose of your experiment, the variables used, and the predicted outcome of your experiment. It is important to note that a hypothesis must be testable. That means that you should be able to test your hypothesis through experimentation.​ Your hypothesis must either be supported or falsified by your experiment. An example of a good hypothesis is: If there is a relation between listening to music and heart rate, then listening to music will cause a person’s resting heart rate to either increase or decrease.


Once you’ve developed a hypothesis, you must design and conduct an experiment that will test it. You should develop a procedure that states very clearly how you plan to conduct your experiment. It is important that you include and identify a controlled variable or dependent variable in your procedure. Controls allow us to test a single variable in an experiment because they are unchanged. We can then make observations and comparisons between our controls and our independent variables (things that change in the experiment) to develop an accurate conclusion.​


The results are where you report what happened in the experiment. That includes detailing all observations and data made during your experiment. Most people find it easier to visualize the data by charting or graphing the information.​


The final step of the scientific method is developing a conclusion. This is where all of the results from the experiment are analyzed and a determination is reached about the hypothesis. Did the experiment support or reject your hypothesis? If your hypothesis was supported, great. If not, repeat the experiment or think of ways to improve your procedure.


Glycolysis: The First Stage in Cellular Respiration

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Diagram showing the process of glycolysis
Thomas Shafee / CC BY 4.0 / Wikimedia Commons


By Regina BaileyUpdated on January 22, 2020

Glycolysis, which translates to “splitting sugars”, is the process of releasing energy within sugars. In glycolysis, a six-carbon sugar known as glucose is split into two molecules of a three-carbon sugar called pyruvate. This multistep process yields two ATP molecules containing free energy, two pyruvate molecules, two high energy, electron-carrying molecules of NADH, and two molecules of water.


  • Glycolysis is the process of breaking down glucose.
  • Glycolysis can take place with or without oxygen.
  • Glycolysis produces two molecules of pyruvate, two molecules of ATP, two molecules of NADH, and two molecules of water.
  • Glycolysis takes place in the cytoplasm.
  • There are 10 enzymes involved in breaking down sugar. The 10 steps of glycolysis are organized by the order in which specific enzymes act upon the system.

Glycolysis can occur with or without oxygen. In the presence of oxygen, glycolysis is the first stage of cellular respiration. In the absence of oxygen, glycolysis allows cells to make small amounts of ATP through a process of fermentation.https://d41aca0362ffc43c95988f07e682d388.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Glycolysis takes place in the cytosol of the cell’s cytoplasm. A net of two ATP molecules are produced through glycolysis (two are used during the process and four are produced.) Learn more about the 10 steps of glycolysis below.

Step 1

The enzyme hexokinase phosphorylates or adds a phosphate group to glucose in a cell’s cytoplasm. In the process, a phosphate group from ATP is transferred to glucose producing glucose 6-phosphate or G6P. One molecule of ATP is consumed during this phase.

Step 2

The enzyme phosphoglucomutase isomerizes G6P into its isomer fructose 6-phosphate or F6P. Isomers have the same molecular formula as each other but different atomic arrangements.

Step 3

The kinase phosphofructokinase uses another ATP molecule to transfer a phosphate group to F6P in order to form fructose 1,6-bisphosphate or FBP. Two ATP molecules have been used so far.

Step 4

The enzyme aldolase splits fructose 1,6-bisphosphate into a ketone and an aldehyde molecule. These sugars, dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GAP), are isomers of each other.

Step 5

The enzyme triose-phosphate isomerase rapidly converts DHAP into GAP (these isomers can inter-convert). GAP is the substrate needed for the next step of glycolysis.

Step 6

The enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH) serves two functions in this reaction. First, it dehydrogenates GAP by transferring one of its hydrogen (H⁺) molecules to the oxidizing agent nicotinamide adenine dinucleotide (NAD⁺) to form NADH + H⁺.

Next, GAPDH adds a phosphate from the cytosol to the oxidized GAP to form 1,3-bisphosphoglycerate (BPG). Both molecules of GAP produced in the previous step undergo this process of dehydrogenation and phosphorylation.

Step 7

The enzyme phosphoglycerokinase transfers a phosphate from BPG to a molecule of ADP to form ATP. This happens to each molecule of BPG. This reaction yields two 3-phosphoglycerate (3 PGA) molecules and two ATP molecules.

Step 8

The enzyme phosphoglyceromutase relocates the P of the two 3 PGA molecules from the third to the second carbon to form two 2-phosphoglycerate (2 PGA) molecules.

Step 9

The enzyme enolase removes a molecule of water from 2-phosphoglycerate to form phosphoenolpyruvate (PEP). This happens for each molecule of 2 PGA from Step 8.

Step 10

The enzyme pyruvate kinase transfers a P from PEP to ADP to form pyruvate and ATP. This happens for each molecule of PEP. This reaction yields two molecules of pyruvate and two ATP molecules.

Cephalization: Definition and Examples

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Humans and other vertebrate show cephalization.
Duke Harbovitch / EyeEm / Getty Images


By Anne Marie Helmenstine, Ph.D.Updated on January 28, 2020

In zoology, cephalization is the evolutionary trend toward concentrating nervous tissue, the mouth, and sense organs toward the front end of an animal. Fully cephalized organisms have a head and brain, while less cephalized animals display one or more regions of nervous tissue. Cephalization is associated with bilateral symmetry and movement with the head facing forward.

Key Takeaways: Cephalization

  • Cephalization is defined as the evolutionary trend toward nervous system centralization and the development of a head and brain.
  • Cephalized organisms display bilateral symmetry. Sense organs or tissues are concentrated on or near the head, which is at the front of the animal as it moves forward. The mouth is also located near the front of the creature.
  • Advantages of cephalization are development of a complex neural system and intelligence, clustering of senses to help an animal rapidly sense food and threats, and superior analysis of food sources.
  • Radially symmetrical organisms lack cephalization. Nervous tissue and senses typically receive information from multiple directions. The oral orifice is often near the middle of the body.


Cephalization offers an organism three advantages. First, it allows for the development of a brain. The brain acts as a control center to organize and control sensory information. Over time, animals can evolve complex neural systems and develop higher intelligence. The second advantage of cephalization is that sense organs can cluster at the front of the body. This helps a forward-facing organism efficiently scan its environment so it can locate food and shelter and avoid predators and other dangers. Basically, the front end of the animal senses stimuli first, as the organism moves forward. Third, cephalization trends toward placing the mouth closer to the sense organs and brain. The net effect is that an animal can quickly analyze food sources. Predators often have special sense organs near the oral cavity to gain information about prey when it’s too close for vision and hearing. For example, cats have vibrissae (whiskers) that sense prey in the dark and when it’s too close for them to see. https://df6a02ef4fa89a4672a2a990230c2305.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.htmlSharks have electroreceptors called the ampullae of Lorenzini that allow them to map prey location.

Cephalization results in animals that have heads with brains and sense organs clustered on the head.
 Cephalization results in animals that have heads with brains and sense organs clustered on the head. Mike Schultz / EyeEm / Getty Images

Examples of Cephalization

Three groups of animals display a high degree of cephalization: vertebrates, arthropods, and cephalopod mollusks. Examples of vertebrates include humans, snakes, and birds. Examples of arthropods include lobsters, ants, and spiders. Examples of cephalopods include octopuses, squid, and cuttlefish. Animals from these three groups exhibit bilateral symmetry, forward movement, and well-developed brains. Species from these three groups are considered to be the most intelligent organisms on the planet.

Many more types of animals lack true brains but have cerebral ganglia. While the “head” may be less clearly defined, it’s easy to identify the front and rear of the creature. Sense organs or sensory tissue and the mouth or oral cavity is near the front. Locomotion places the cluster of nervous tissue, sense organs, and mouth toward the front. While the nervous system of these animals is less centralized, associative learning still occurs. Snails, flatworms, and nematodes are examples of organisms with a lesser degree of cephalization.

Clusters of neurons around a jellyfish bell allow it to process 360 degrees of sensory input.
 Clusters of neurons around a jellyfish bell allow it to process 360 degrees of sensory input. Feria Hikmet Noraddin / EyeEm / Getty Images

Animals That Lack Cephalization

Cephalization doesn’t offer an advantage to free-floating or sessile organisms. Many aquatic species display radial symmetry. Examples include echinoderms (starfish, sea urchins, sea cucumbers) and cnidarians (corals, anemones, jellyfish). Animals that can’t move or are subject to currents must be able to find food and defend against threats from any direction. Most introductory textbooks list these animals as acephalic or lacking cephalization. While it’s true none of these creatures has a brain or central nervous system, their neural tissue is organized to allow rapid muscular excitation and sensory processing. Modern invertebrate zoologists have identified nerve nets in these creatures. Animals that lack cephalization are not less-evolved than those with brains. It’s simply that they are adapted to a different type of habitat.

What Is Resource Partitioning? Definition and Examples

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Animals Competing for Resources
 Intraspecific competition refers to competition for limited resources by individual organisms of the same species. Cappi Thompson/Moment/Getty Images


By Regina BaileyUpdated on April 22, 2019

Resource partitioning is the division of limited resources by species to help avoid competition in an ecological niche. In any environment, organisms compete for limited resources, so organisms and different species have to find ways to coexist with one another. By examining how and why resources are allocated in a particular niche, scientists can better understand the complex ecological interactions between and in species. Common examples of resource partitioning include the Anole lizards and a number of bird species.https://f544c3bcedef556f84832b0ed9dd561e.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Key Takeaways

  • The division of resources by species to help avoid competition in an ecological niche is called resource partitioning.
  • Intraspecific competition denotes competition for resources by individuals of the same species.
  • Interspecific competition is the competition for resources by individuals of different species.
  • By studying resource partitioning, scientists can understand how the addition or removal of a species may impact the overall usage of resources in a given habitat or niche.

Resource Partitioning Definition

The original concept of resource partitioning refers to the evolutionary adaptations in species as a response to the evolutionary pressure from interspecific competition. The more common basic biological usage is based on the different uses of resources by species in a particular niche and not on the specific evolutionary origin of such differences. This article explores the latter convention.https://f544c3bcedef556f84832b0ed9dd561e.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

When organisms compete for limited resources, there are two primary types of competition: intraspecific and interspecific. As the prefixes denote, intraspecific competition refers to competition for limited resources by individual organisms of the same species, while interspecific competition refers to the competition for limited resources by individuals of different species.

When species compete for the exact same resources, one species typically has the advantage over another, even if only slightly so. The complete competition maxim states that complete competitors cannot coexist. The species with the advantage will persist in the long term. The weaker species will either become extinct or will transition to occupying a different ecological niche.https://f544c3bcedef556f84832b0ed9dd561e.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Habitat Partitioning Examples

One way that species can partition resources is by living in different areas of a habitat versus their competitors. One common example is the distribution of lizards in the Caribbean islands. The lizards mostly eat the same types of food—insects. However, they can live in different microhabitats within the context of their larger habitat. For example, some lizards can live on the forest floor while others may live higher up in the habitat in trees. This differentiation and partitioning of resources based on their physical location allows the different species to coexist more effectively with one another.https://f544c3bcedef556f84832b0ed9dd561e.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Food Partitioning Examples

Additionally, species can more effectively coexist based on food partitioning. For example, among species of lemur monkeys, food may be discriminated by the chemical characteristics of the food. Food partitioning based on plant chemistry can play an important role. This allows different species to coexist while eating similar yet chemically different foods.

Similarly, species may have an affinity for different parts of the same food. For example, one species may prefer a different part of the plant than another species, allowing them to effectively coexist. Some species may prefer the leaves of the plant while others prefer the plant stems.

Species can also partition food based on other characteristics such as different activity patterns. One species may consume most of their food during a certain time of day while another may be more active at night.

Long-Term Effects of Resource Partitioning

By partitioning out resources, species can have long-term coexistence with one another in the same habitat. This allows both species to survive and thrive rather than one species causing the other to go extinct, as in the case of complete competition. The combination of intraspecific and interspecific competition is important in relation to species. When different species occupy slightly different niches in relation to resources, the limiting factor for population size becomes more about intraspecific competition than interspecific competition.

Similarly, humans can have profound effects on ecosystems, particularly in causing species to go extinct. The study of resource partitioning by scientists can help us understand how the removal of a species may impact the overall allocation and usage of resources both in a particular niche and in the broader environment.

Taxonomy and Organism Classification

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Carolus Linnaeus
 circa 1760: Swedish physician and botanist Carl von Linnaeus (1707-1778), founder of the modern system of binomial nomenclature for plants. Original Publication: From a copy by Pasch of an original painting. Hulton Archive / Stringer/ Hulton Archive/ Getty Images


By Regina BaileyUpdated on November 05, 2019

taxonomy is a hierarchical scheme for classifying and identifying organisms. It was developed by Swedish scientist Carl Linnaeus in the 18th century. In addition to being a valuable tool for biological classification, Linnaeus’s system is also useful for scientific naming. The two main features of this taxonomy system, binomial nomenclature and categorical classification, make it convenient and effective.https://d2a092ac1e684daccf3f9837956709c3.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Binomial Nomenclature

The first feature of Linnaeus’s taxonomy, which makes naming organisms uncomplicated, is the use of binomial nomenclature. This naming system devises a scientific name for an organism based on two terms: The name of the organism’s genus and the name of its species. Both of these terms are italicized and the genus name is capitalized when writing.https://d2a092ac1e684daccf3f9837956709c3.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Example: The bionomical nomenclature for humans is Homo sapiens. The genus name is Homo and the species name is sapiens. These terms are unique and ensure that no two organisms have the same scientific name.

The foolproof method of naming organisms ensures consistency and clarity across the field of biology and makes Linnaeus’s system simple.

Classification Categories

The second feature of Linnaeus’s taxonomy, which simplifies organism ordering, is categorical classification. This means narrowing organism types into categories but this approach has undergone significant changes since its inception. The broadest of these categories within Linnaeus’s original system is known as kingdom and he divided all of the world’s living organisms into only an animal kingdom and plant kingdom.https://d2a092ac1e684daccf3f9837956709c3.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Linnaeus further divided organisms by shared physical characteristics into classes, orders, genera, and species. These categories were revised to include kingdom, phylum, class, order, family, genus, and species over time. As more scientific advancements and discoveries were made, domain was added to the taxonomic hierarchy and is now the broadest category. The kingdom system of classification was all but replaced by the current domain system of classification.

Domain System

Organisms are now grouped primarily according to differences in ribosomal ​RNA structures, not physical properties. The domain system of classification was developed by Carl Woese and places organisms under the following three domains: 

  • Archaea: This domain includes prokaryotic organisms (which lack a nucleus) that differ from bacteria in membrane composition and RNA. They are extremophiles capable of living in some of the most inhospitable conditions on earth, such as hydrothermal vents.
  • Bacteria: This domain includes prokaryotic organisms with unique cell wall compositions and RNA types. As part of the human microbiota, bacteria are vital to life. However, some bacteria are pathogenic and cause disease.
  • Eukarya: This domain includes eukaryotes or organisms with a true nucleus. Eukaryotic organisms include plants, animals, protists, and fungi.

Under the domain system, organisms are grouped into six kingdoms which include Archaebacteria (ancient bacteria), Eubacteria (true bacteria), Protista, Fungi, Plantae, and Animalia. The process of classifying organisms by categories was conceived by Linnaeus and has been adapted since.

Taxonomy Example

The table below includes a list of organisms and their classification within this taxonomy system using the eight major categories. Notice how closely dogs and wolves are related. They are similar in every aspect except species name.

Taxonomic Hierarchy Example
 Brown BearHouse CatDogKiller WhaleWolfTarantula
SpeciesUrsus arctosFelis catusCanis familiarisOrcinus orcaCanis lupusTheraphosa blondi

Taxonomic Classification Example

Intermediate Categories

Taxonomic categories can be even more precisely divided into intermediate categories such as subphyla, suborders, superfamilies, and superclasses. A table of this taxonomy scheme appears below. Each main category of classification has its own subcategory and supercategory.

Taxonomic Hierarchy With Subcategory and Supercategory
KingdomSubkingdomSuperkingdom (Domain)

Biology Prefixes and Suffixes: -ase

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Computer illustration of a DNA Polymerase molecule
 DNA polymerase molecule.Callista Image / Getty Images


By Regina BaileyUpdated on February 24, 2019

The suffix “-ase” is used to signify an enzyme. In enzyme naming, an enzyme is denoted by adding -ase to the end of the name of the substrate on which the enzyme acts. It is also used to identify a particular class of enzymes that catalyze a specific type of reaction.https://615dcb164c6d628464b69029c4da750d.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Examples of “Ase” Suffixes

Below, find some examples of words ending in -ase, along with a breakdown of different root words in their name and their definition.https://615dcb164c6d628464b69029c4da750d.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

A: Acetylcholinesterase to C: Collagenase

Acetylcholinesterase (acetyl-cholin-ester-ase): This nervous system enzyme, also present in muscle tissue and red blood cells, catalyzes the hydrolysis of the neurotransmitter acetylcholine. It functions to inhibit the stimulation of muscle fibers.

Amylase (amyl-ase): Amylase is a digestive enzyme that catalyzes the decomposition of starch into sugar. It is produced in salivary glands and the pancreas.

Carboxylase (carboxyl-ase): This class of enzymes catalyze the release of carbon dioxide from certain organic acids.

Collagenase (collagen-ase): Collagenases are enzymes that degrade collagen. They function in wound repair and are used to treat some connective tissue diseases.

D: Dehydrogenase to H: Hydrolase

Dehydrogenase (de-hydrogen-ase): Dehydrogenase enzymes promote the removal and transfer of hydrogen from one biological molecule to another. Alcohol dehydrogenase, found abundantly in the liver, catalyzes the oxidation of alcohol to aid in alcohol detoxification.

Deoxyribonuclease (de-oxy-ribo-nucle-ase): This enzyme degrades DNA by catalyzing the breaking of phosphodiester bonds in the sugar-phosphate backbone of DNA. It is involved in the destruction of DNA that occurs during apoptosis (programmed cell death).https://615dcb164c6d628464b69029c4da750d.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Endonuclease (endo-nucle-ase): This enzyme breaks bonds within nucleotide chains of DNA and RNA molecules. Bacteria use endonucleases to cleave DNA from invading viruses.

Histaminase (histamin-ase): Found in the digestive system, this enzyme catalyzes the removal of the amino group from histamine. Histamine is released during an allergic reaction and promotes an inflammatory response. Histaminase inactivates histamine and is used in the treatment of allergies.

Hydrolase (hydro-lase): This class of enzymes catalyzes the hydrolysis of a compound. In hydrolysis, water is used to break chemical bonds and split compounds into other compounds. Examples of hydrolases include lipases, esterases, and proteases.https://615dcb164c6d628464b69029c4da750d.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

I: Isomerase to N: Nuclease

Isomerase (isomer-ase): This class of enzymes catalyzes reactions that structurally rearrange the atoms in a molecule changing it from one isomer to another.

Lactase (lact-ase): Lactase is an enzyme that catalyzes the hydrolysis of lactose to glucose and galactose. This enzyme is found in high concentrations in the liver, kidneys, and mucous lining of the intestines.

Ligase (lig-ase): Ligase is a type of enzyme that catalyzes the joining together of molecules. For example, DNA ligase joins DNA fragments together during DNA replication.

Lipase (lip-ase): Lipase enzymes break down fats and lipids. An important digestive enzyme, lipase converts triglycerides into fatty acids and glycerol. Lipase is produced mainly in the pancreas, mouth, and stomach.

Maltase (malt-ase): This enzyme converts the disaccharide maltose to glucose. It is produced in the intestines and used in the digestion of carbohydrates.

Nuclease (nucle-ase): This group of enzymes catalyzes the hydrolysis of bonds between nucleotide bases in nucleic acids. Nucleases split DNA and RNA molecules and are important for DNA replication and repair.

P: Peptidase to T: Transferase

Peptidase (peptid-ase): Also called protease, peptidase enzymes break peptide bonds in proteins, thereby forming amino acids. Peptidases function in the digestive system, immune system, and blood circulatory system.

Phospholipase (phospho-lip-ase): The conversion of phospholipids to fatty acids by the addition of water is catalyzed by a group of enzymes called phospholipases. These enzymes play an important role in cell signaling, digestion, and cell membrane function.

Polymerase (polymer-ase): Polymerase is a group of enzymes that builds polymers of nucleic acids. These enzymes make copies of DNA and RNA molecules, which is required for cell division and protein synthesis.

Ribonuclease (ribo-nucle-ase): This class of enzymes catalyzes the break down of RNA molecules. Ribonucleases inhibit protein synthesis, promote apoptosis, and protect against RNA viruses.

Sucrase (sucr-ase): This group of enzymes catalyzes the decomposition of sucrose to glucose and fructose. Sucrase is produced in the small intestine and aids in the digestion of sugar. Yeasts also produce sucrase.

Transcriptase (transcript-ase): Transcriptase enzymes catalyze DNA transcription by producing RNA from a DNA template. Some viruses (retroviruses) have the enzyme reverse transcriptase, which makes DNA from an RNA template.

Transferase (transfer-ase): This class of enzymes aids in the transfer of a chemical group, such as an amino group, from one molecule to another. Kinases are examples of transferase enzymes that transfer phosphate groups during phosphorylation.

Why Men Are Typically Taller Than Women

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man and woman walk together on the beach
SolStock / Getty Images 


By Regina BaileyUpdated on January 31, 2019

While studying genetic factors behind different traits in men and women, University of Helsinki researchers have identified a genetic variant on the X sex chromosome that accounts for height differences between the sexes. Sex cells, produced by male and female gonads, contain either an X or a Y chromosome. The fact that females have two X chromosomes and males only have one X chromosome must be taken into account when attributing the difference in traits to variants on the X chromosome.https://02d9b5ba5255720adff4848b3f66af45.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

According to the study’s head researcher, Professor Samuli Ripatti, “The double dose of X-chromosomal genes in women could cause problems during the development. To prevent this, there is a process by which one of the two copies of the X chromosome present in the cell is silenced. When we realized that the height associated variant we identified was nearby a gene that is able to escape the silencing we were particularly excited.” The height variant identified influences a gene that is involved in cartilage development. Individuals that possess the height variant tend to be shorter than average. Since women have two copies of the X chromosome variant, they tend to be shorter than men.

Organ Systems Study Guide

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Digital illustration of the Human Digestive System
Science Photo Library / Getty Images


By Regina Bailey

Updated on February 10, 2019

The human body is made up of several organ systems that work as one unit. The major organ systems of the body work together, either directly or indirectly, to keep the body functioning normally.https://d17e09788ff3625e7a76d1f0edac5009.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Organ Systems

Some of the major organ systems of the body include:

Circulatory System: The circulatory system circulates blood by pulmonary and systemic circuits. These pathways transport blood between the heart and the rest of the body.https://d17e09788ff3625e7a76d1f0edac5009.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Digestive System: The digestive system processes the foods we eat in order to supply nutrients to the body. These nutrients are transported throughout the body by the circulatory system.

Endocrine System: The endocrine system secretes hormones to regulate organ function and body processes, such as growth and maintaining homeostasis.

Integumentary System: The integumentary system covers the exterior of the body, protecting internal structures from damage, germs, and dehydration.

Nervous System: The nervous system consists of the brainspinal cord, and nerves. This system monitors and controls all body systems and responds to external influences on the body.

Reproductive System: The reproductive system ensures the survival of a species through the production of offspring by sexual reproduction. Male and female reproductive organs are also endocrine organs that secrete hormones to regulate sexual development.

Parasitism: Definition and Examples

What Are Parasites and Why Do We Need Them?

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The wood tick is an example of an ectoparasite.
ArtBoyMB / Getty Images


By Anne Marie Helmenstine, Ph.D.Updated on October 24, 2019

Parasitism is defined as a relationship between two species in which one organism (parasite) lives on or within the other organism (host), causing the host some degree of harm. A parasite reduces its host’s fitness but increases its own fitness, usually by gaining food and shelter.https://f762bc7ce67e04320f8aa08be3154f86.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Key Takeaways: Parasitism

  • Parasitism is a type of symbiotic relationship in which one organism benefits at the expense of another.
  • The species that benefits is called the parasite, while the one that is harmed is called the host.
  • Over half of all known species are parasites. Parasites are found in all biological kingdoms.
  • Examples of human parasites include roundworms, leeches, ticks, lice, and mites.

The term “parasite” comes from the Greek word parasitos, which means “one who eats at the table of another.” The study of parasites and parasitism is called parasitology.https://f762bc7ce67e04320f8aa08be3154f86.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

There are parasites belonging to every biological kingdom (animals, plants, fungi, protozoa, bacteria, viruses). In the animal kingdom, every parasite has a free-living counterpart. Examples of parasites include mosquitoes, mistletoe, roundworms, all viruses, ticks, and the protozoan that causes malaria.

Parasitism vs. Predation

Both parasites and predators rely on another organism for one or more resources, but they have numerous differences. Predators kill their prey in order to consume it. As a result, predators tend to be physically larger and/or stronger than their prey. Parasites, on the other hand, tend to be much smaller than their host and do not normally kill the host. Instead, a parasite lives on or within the host for a period of time. Parasites also tend to reproduce much more quickly than hosts, which is not usually the case in predator-prey relationships.https://f762bc7ce67e04320f8aa08be3154f86.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Parasitism vs. Mutualism vs. Commensalism

Parasitism, mutualism, and commensalism are three types of symbiotic relationships between organisms. In parasitism, one species benefits at the expense of the other. In mutualism, both species benefit from the interaction. In commensalism, one species benefits, while the other is neither harmed nor helped.

Types of Parasitism

There are multiple ways to classify types of parasitism.https://f762bc7ce67e04320f8aa08be3154f86.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Parasites may be grouped according to where they live. Ectoparasites, such as fleas and ticks, live on the surface of a host. Endoparasites, such as intestinal worms and protozoa in blood, live inside a host’s body. Mesoparasites, such as some copepods, enter the opening of a host body and partially embed themselves.

The human head louse is a directly-transmitted obligate ectoparasite.
 The human head louse is a directly-transmitted obligate ectoparasite. SCIEPRO / Getty Images

The life cycle can be a basis for classifying parasites. An obligate parasite requires a host in order to complete its life cycle. A facultative parasite can complete its life cycle without a host. Sometimes location and life cycle requirements may be combined. For example, there are obligate intracellular parasites and facultative intestinal parasites.https://f762bc7ce67e04320f8aa08be3154f86.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Parasites may be classified according to their strategy. There are six major parasite strategies. Three relate to parasite transmission:https://f762bc7ce67e04320f8aa08be3154f86.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

  • Directly transmitted parasites, such as fleas and mites, reach their host on their own.
  • Trophically transmitted parasites, such as trematodes and roundworms, are eaten by their host.
  • Vector transmitted parasites rely on an intermediate host to transport them to their definitive host. An example of a vector transmitted parasite is the protozoan that causes sleeping sickness (Trypanosoma), which is transported by biting insects.

The other three strategies involve the parasite’s effect on its host:

  • Parasitic castrators either partly or fully inhibit a host’s reproductive ability but allow the organism to live. The energy the host would have put toward reproduction is diverted toward supporting the parasite. An example is the barnacle Sacculina, which degenerates the gonads of crabs such that males develop the appearance of females.
  • Parasitoids eventually kill their hosts, making them nearly predators. All examples of parasitoids are insects that lay their eggs on or inside the host. When the egg hatches, the developing juvenile serves as food and shelter.
  • micropredator attacks more than one host so that most host organisms survive. Examples of micropredators include vampire bats, lampreys, fleas, leeches, and ticks.

Other types of parasitism include brood parasitism, where a host raises the young of the parasite (e.g., cuckoos); kleptoparasitism, in which a parasite steals the host’s food (e.g., skuas stealing food from other birds); and sexual parasitism, in which males rely on females for survival (e.g., anglerfish).

The banded caterpillar parasite wasp uses its long ovipositor to lay eggs inside its host.
 The banded caterpillar parasite wasp uses its long ovipositor to lay eggs inside its host. Louise Docker Sydney Australia / Getty Images

Why We Need Parasites

Parasites harm their hosts, so it’s tempting to think they should be eradicated. Yet, at least half of all known species are parasitic. Parasites serve an important role in an ecosystem. They help control dominant species, allowing for competition and diversity. Parasites transfer genetic material between species, serving a role in evolution. In general, the presence of parasites is a positive indication of ecosystem health.

6 Things You Should Know About Biological Evolution

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Close up of white and orange tigers lounging in grass.
 White tigers have white fur as a result of biological evolution.Irfan Saghir Mirza Photos / Moment / Getty Images


By Regina BaileyUpdated on October 26, 2019

Biological evolution is defined as any genetic change in a population that is inherited over several generations. These changes may be small or large, noticeable or not so noticeable.https://2367a31837509a184f61ae88fe8d8003.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

For an event to be considered an instance of evolution, changes have to occur on the genetic level of a population and be passed on from one generation to the next. This means that the genes, or more specifically, the alleles in the population change and are passed on.https://2367a31837509a184f61ae88fe8d8003.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

These changes are noticed in the phenotypes (expressed physical traits that can be seen) of the population.

A change on the genetic level of a population is defined as a small-scale change and is called microevolution. Biological evolution also includes the idea that all of life is connected and can be traced back to one common ancestor. This is called macroevolution.

What Evolution Is Not

Biological evolution is not defined as simply change over time. Many organisms experience changes over time, such as weight loss or gain.

These changes are not considered instances of evolution because they are not genetic changes that can be passed on to the next generation.

Is Evolution a Theory?

Evolution is a scientific theory that was proposed by Charles Darwin. A scientific theory gives explanations and predictions for naturally occurring phenomena based on observations and experimentations. This type of theory attempts to explain how events seen in the natural world work.

The definition of a scientific theory differs from the common meaning of theory, which is defined as a guess or a supposition about a particular process. In contrast, a good scientific theory must be testable, falsifiable, and substantiated by factual evidence.

When it comes to a scientific theory, there is no absolute proof. It’s more a case of confirming the reasonability of accepting a theory as a viable explanation for a particular event.

What Is Natural Selection?

Natural selection is the process by which biological evolutionary changes take place. Natural selection acts on populations and not individuals. It is based on the following concepts:

  • Individuals in a population have different traits that can be inherited.
  • These individuals produce more young than the environment can support.
  • The individuals in a population that are best suited to their environment will leave more offspring, resulting in a change in the genetic makeup of a population.

The genetic variations that arise in a population happen by chance, but the process of natural selection does not. Natural selection is the result of the interactions between genetic variations in a population and the environment.

The environment determines which variations are more favorable. Individuals that possess traits that are better suited to their environment will survive to produce more offspring than other individuals. More favorable traits are thereby passed on to the population as a whole.

Examples of genetic variation in a population include the modified leaves of carnivorous plants, cheetahs with stripes, snakes that flyanimals that play dead, and animals that resemble leaves.

How Does Genetic Variation Occur?

Genetic variation occurs mainly through DNA mutation, gene flow (movement of genes from one population to another) and sexual reproduction. Since environments are unstable, populations that are genetically variable will be able to adapt to changing situations better than those that do not contain genetic variations.

Sexual reproduction allows for genetic variations to occur through genetic recombination. Recombination occurs during meiosis and provides a way for producing new combinations of alleles on a single chromosomeIndependent assortment during meiosis allows for an indefinite number of combinations of genes.

Sexual reproduction makes it possible to assemble favorable gene combinations in a population or to remove unfavorable gene combinations from a population. Populations with more favorable genetic combinations will survive in their environment and reproduce more offspring than those with less favorable genetic combinations.

Biological Evolution Versus Creation

The theory of evolution has caused controversy from the time of its introduction until today. The controversy stems from the perception that biological evolution is at odds with religion concerning the need for a divine creator.

Evolutionists contend that evolution does not address the issue of whether God exists, but attempts to explain how natural processes work.

In doing so, however, there is no escaping the fact that evolution contradicts certain aspects of some religious beliefs. For example, the evolutionary account for the existence of life and the biblical account of creation are quite different.

Evolution suggests that all life is connected and can be traced back to one common ancestor. A literal interpretation of biblical creation suggests that life was created by an all-powerful, supernatural being (God).

Still, others have tried to merge these two concepts by contending that evolution does not exclude the possibility of the existence of God, but merely explains the process by which God created life. This view, however, still contradicts a literal interpretation of creation as presented in the Bible.

A major bone of contention between the two views is the concept of macroevolution. For the most part, evolutionists and creationists agree that microevolution does occur and is visible in nature.

Macroevolution, however, refers to the process of evolution that takes place on the level of species, in which one species evolves from another species. This is in stark contrast to the biblical view that God was personally involved in the formation and creation of living organisms.

For now, the evolution/creation debate continues and it appears that the differences between these two views are not likely to be settled soon.

Diffusion: Passive Transport and Facilitated Diffusion

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PRINT Science

By Regina BaileyUpdated on August 20, 2019

Diffusion is the tendency of molecules to spread into an available space. This tendency is a result of the intrinsic thermal energy (heat) found in all molecules at temperatures above absolute zero.

A simplified way to understand this concept is to imagine a crowded subway train in New York City. At rush hour most want to get to work or home as soon as possible so lots of people pack onto the train. Some people may be standing not more than a breath’s distance away from each other. As the train stops at stations, passengers get off. Those passengers who had been crowded up against each other start to spread out. Some find seats, others move further away from the person they had just been standing next to.

This same process happens with molecules. Without other outside forces at work, substances will move or diffuse from a more concentrated environment to a less concentrated environment. No work is performed for this to happen. Diffusion is a spontaneous process. This process is called passive transport.

Diffusion and Passive Transport

Passive Diffusion
 Illustration of passive diffusion. Steven Berg

Passive transport is the diffusion of substances across a membrane. This is a spontaneous process and cellular energy is not expended. Molecules will move from where the substance is more concentrated to where it is less concentrated.

“This cartoon illustrates passive diffusion. The dashed line is intended to indicate a membrane that is permeable to the molecules or ions illustrated as red dots. Initially, all of the red dots are within the membrane. As time passes, there is net diffusion of the red dots out of the membrane, following their concentration gradient. When the concentration of red dots is the same inside and outside of the membrane the net diffusion ceases. However, the red dots still diffuse into and out of the membrane, but the rates of the inward and outward diffusion are the same resulting in a net diffusion of O.”—Dr. Steven Berg, professor emeritus, cellular biology, Winona State University.

Although the process is spontaneous, the rate of diffusion of different substances is affected by membrane permeability. Since cell membranes are selectively permeable (only some substances can pass), different molecules will have different rates of diffusion.

For instance, water diffuses freely across membranes, an obvious benefit for cells since water is crucial to many cellular processes. Some molecules, however, must be helped across the phospholipid bilayer of the cell membrane through a process called facilitated diffusion.https://e44d3bef2da4a2f253030dccd63bb26d.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Facilitated Diffusion

Facilitated Diffusion
 Facilitated diffusion involves the use of a protein to facilitate the movement of molecules across the membrane. In some cases, molecules pass through channels within the protein. In other cases, the protein changes shape, allowing molecules to pass through. Mariana Ruiz Villarreal

Facilitated diffusion is a type of passive transport that allows substances to cross membranes with the assistance of special transport proteins. Some molecules and ions such as glucose, sodium ions, and chloride ions are unable to pass through the phospholipid bilayer of cell membranes. Through the use of ion channel proteins and carrier proteins that are embedded in the cell membrane,​ these substances can be transported into the cell.

Ion channel proteins allow specific ions to pass through the protein channel. The ion channels are regulated by the cell and are either open or closed to control the passage of substances into the cell. Carrier proteins bind to specific molecules, change shape, and then deposit the molecules across the membrane. Once the transaction is complete the proteins return to their original position.https://e44d3bef2da4a2f253030dccd63bb26d.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html


Osmosis in Blood Cells
 Osmosis is a special case of passive transport. These blood cells have been placed in solutions with different solute concentrations. Mariana Ruiz Villarreal

Osmosis is a special case of passive transport. In osmosis, water diffuses from a hypotonic (low solute concentration) solution to a hypertonic (high solute concentration) solution. Generally speaking, the direction of water flow is determined by the solute concentration and not by the nature of the solute molecules themselves.

For example, take a look at blood cells that are placed in salt water solutions of different concentrations (hypertonic, isotonic, and hypotonic). 

  • hypertonic concentration means that the salt water solution contains a higher concentration of solute and a lower concentration of water than the blood cells. Fluid would flow from the area of low solute concentration (the blood cells) to an area of high solute concentration (water solution). As a result, the blood cells will shrink.
  • If the salt water solution is isotonic it would contain the same concentration of solute as the blood cells. Fluid would flow equally between the blood cells and the water solution. As a result, the blood cells will remain the same size.
  • The opposite of hypertonic, a hypotonic solution means that the salt water solution contains a lower concentration of solute and a higher concentration of water than the blood cells. Fluid would flow from the area of low solute concentration (water solution) to an area of high solute concentration (the blood cells). As a result, the blood cells will swell and may even burst

How Steroid Hormones Work

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Male and Female Hormones
 Male and Female Hormones. JosA Carlos Pires Pereira/E+/Getty Images


By Regina BaileyUpdated on August 19, 2019

Hormones are molecules produced and secreted by endocrine glands in the body. Hormones are released into the blood and travel to other parts of the body where they bring about specific responses from specific cellsSteroid hormones are derived from cholesterol and are lipid-soluble molecules. Examples of steroid hormones include the sex hormones (androgens, estrogens, and progesterone) produced by male and female gonads and hormones of the adrenal glands (aldosterone, cortisol, and androgens).https://347a50d8260a63aa8ba8f322a2a176be.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Key Takeaways: Steroid Hormones

  • Steroid hormones are fat-soluble molecules derived from cholesterol. They are produced by certain endocrine organs and glands and released into the bloodstream to reach target cells.
  • Steroid hormones include sex hormones and adrenal gland hormones. Testosterone, estrogens, and cortisol are examples of steroid hormones.
  • Steroid hormones act on cells by passing through the cell membrane, entering the nucleus, binding to DNA, and initiating gene transcription and protein production.
  • Anabolic steroid hormones are synthetic molecules that mimic the action of testosterone. Illegal use and abuse of these hormones can lead to a number of negative health consequences.

How Steroid Hormones Work

Steroid hormones cause changes within a cell by first passing through the cell membrane of the target cell. Steroid hormones, unlike non-steroid hormones, can do this because they are fat-soluble. Cell membranes are composed of a phospholipid bilayer which prevents fat-insoluble molecules from diffusing into the cell.https://347a50d8260a63aa8ba8f322a2a176be.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Lipid-soluble hormones
 This is an illustration of lipid-soluble hormone binding and protein production in a cell.  OpenStax, Anatomy & Physiology/Creative Commons Attribution 3.0

Once inside the cell, the steroid hormone binds with a specific receptor found only in the cytoplasm of the target cell. The receptor bound steroid hormone then travels into the nucleus and binds to another specific receptor on the chromatin. Once bound to the chromatin, this steroid hormone-receptor complex calls for the production of specific RNA molecules called messenger RNA (mRNA) by a process called transcription. The mRNA molecules are then modified and transported to the cytoplasm. The mRNA molecules code for the production of proteins through a process called translation. These proteins can be used to build muscle.

Steroid Hormone Mechanism of Action

The steroid hormone mechanism of action can be summarized as follows:https://347a50d8260a63aa8ba8f322a2a176be.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

  1. Steroid hormones pass through the cell membrane of the target cell.
  2. The steroid hormone binds with a specific receptor in the cytoplasm.
  3. The receptor bound steroid hormone travels into the nucleus and binds to another specific receptor on the chromatin.
  4. The steroid hormone-receptor complex calls for the production of messenger RNA (mRNA) molecules, which code for the production of proteins.

Types of Steroid Hormones

Testosterone molecule
 This is a molecular model of the structure of the male sex hormone testosterone.  Pasieka/Oxford Scientific/Getty Images

Steroid hormones are produced by the adrenal glands and gonads. The adrenal glands sit atop the kidneys and consist of an outer cortex layer and an inner medulla layer. Adrenal steroid hormones are produced in the outer cortex layer. Gonads are the male testes and female are the ovaries.https://347a50d8260a63aa8ba8f322a2a176be.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Adrenal Gland Hormoneshttps://347a50d8260a63aa8ba8f322a2a176be.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

  • Aldosterone: This mineralcorticoid acts on the kidneys promoting the absorption of sodium and water. Aldosterone aids in blood pressure regulation by raising blood volume and blood pressure.
  • Cortisol: This glucocorticoid aids in metabolism regulation by stimulating the production of glucose from non-carbohydrate sources in the liver. Cortisol is also an important anti-inflammatory substance and helps the body deal with stress.
  • Sex Hormones: The adrenal glands produce small amounts of the male sex hormone testosterone and the female sex hormone estrogen.

Gonadal Hormones

  • Testosterone: This male sex hormone is produced by the testes and in small amounts in the female ovaries. Testosterone is responsible for the development of male reproductive organs and male secondary sex characteristics.
  • Estrogens: These female sex hormones are produced in the ovaries. They promote development of female sex characteristics and skeletal growth.
  • Progesterone: This female sex hormone is produced in the ovaries and important for the production and maintenance of the uterine lining during pregnancy. Estrogen and progesterone levels also regulate the menstrual cycle.

Anabolic Steroid Hormones

Anabolic steroids
 Anabolic steroid hormones are synthetic hormones of the male androgen testosterone.  PhotosIndia.com/Getty Images

Anabolic steroid hormones are synthetic substances that are related to the male sex hormones. They have the same mechanism of action within the body. Anabolic steroid hormones stimulate the production of protein, which is used to build muscle. They also lead to an increase in the production of testosterone. In addition to its role in the development of reproductive system organs and sex characteristics, testosterone is also critical in the development of lean muscle mass. Additionally, anabolic steroid hormones promote the release of growth hormone, which stimulates skeletal growth.

Anabolic steroids have therapeutic use and may be prescribed to treat problems such as muscle degeneration associated with disease, male hormone issues, and late onset of puberty. However, some individuals use anabolic steroids illegally to improve athletic performance and build muscle mass. Abuse of anabolic steroid hormones disrupts the normal production of hormones in the body. There are several negative health consequences associated with anabolic steroid abuse. Some of these include infertility, hair loss, breast development in males, heart attacks, and liver tumors. Anabolic steroids also effect the brain causing mood swings and depression.

Biology: The Study of Life

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Moon Jellyfish
 Moon Jellyfish.NOAA Florida Keys National Marine Sanctuary


By Regina BaileyUpdated on May 05, 2019

What is biology? Simply put, it is the study of life, in all of its grandeur. Biology concerns all life forms, from the very small algae to the very large elephant. But how do we know if something is living? For example, is a virus alive or dead? To answer these questions, biologists have created a set of criteria called the “characteristics of life.” 

The Characteristics of Life

Living things include both the visible world of animals, plants, and fungi as well as the invisible world of bacteria and viruses. On a basic level, we can say that life is ordered. Organisms have an enormously complex organization. We’re all familiar with the intricate systems of the basic unit of life, the cell.https://59225f28fb33794639f8e1c6d98be7b8.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Life can “work.” No, this doesn’t mean all animals are qualified for a job. It means that living creatures can take in energy from the environment. This energy, in the form of food, is transformed to maintain metabolic processes and for survival.

Life grows and develops. This means more than just replicating or getting larger in size. Living organisms also have the ability to rebuild and repair themselves when injured.

Life can reproduce. Have you ever seen dirt reproduce? I don’t think so. Life can only come from other living creatures.

Life can respond. Think about the last time you accidentally stubbed your toe. Almost instantly, you flinched back in pain. Life is characterized by this response to stimuli.

Finally, life can adapt and respond to the demands placed on it by the environment. There are three basic types of adaptations that can occur in higher organisms.

  • Reversible changes occur as a response to changes in the environment. Let’s say you live near sea level and you travel to a mountainous area. You may begin to experience difficulty breathing and an increase in heart rate as a result of the change in altitude. These symptoms go away when you go back down to sea level.
  • Somatic changes occur as a result of prolonged changes in the environment. Using the previous example, if you were to stay in the mountainous area for a long time, you would notice that your heart rate would begin to slow down and you would begin to breath normally. Somatic changes are also reversible.
  • The final type of adaptation is called genotypic (caused by genetic mutation). These changes take place within the genetic makeup of the organism and are not reversible. An example would be the development of resistance to pesticides by insects and spiders.

In summary, life is organized, “works,” grows, reproduces, responds to stimuli and adapts. These characteristics form the basis of the study of biology.

Basic Principles of Biology

The foundation of biology as it exists today is based on five basic principles. They are the cell theory, gene theory, evolution, homeostasis, and laws of thermodynamics.

  • Cell Theory: all living organisms are composed of cells. The cell is the basic unit of life.
  • Gene Theory: traits are inherited through gene transmission. Genes are located on chromosomes and consist of DNA.
  • Evolution: any genetic change in a population that is inherited over several generations. These changes may be small or large, noticeable or not so noticeable.
  • Homeostasis: ability to maintain a constant internal environment in response to environmental changes.
  • Thermodynamics: energy is constant and energy transformation is not completely efficient.

Subdiciplines of Biology
The field of biology is very broad in scope and can be divided into several disciplines. In the most general sense, these disciplines are categorized based on the type of organism studied. For example, zoology deals with animal studies, botany deals with plant studies, and microbiology is the study of microorganisms. These fields of study can be broken down further into several specialized sub-disciplines. Some of which include anatomy, cell biologygenetics, and physiology.

Archaea Domain

Extreme Microscopic Organisms

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Methanococcoides Archaea
 This is a colored transmission electron micrograph (TEM) of a section through the Archaebacterium Methanococcoides burtonii. This psychrophilic (cold-loving) Archaebacterium was discovered in 1992 in Ace Lake, Antarctica, and can survive in temperatures as low as -2.5 degrees Celsius. As a methanogenic bacterium, it is able to form methane from carbon dioxide and hydrogen. DR M.ROHDE, GBF/Science Photo Library/Getty Images


By Regina BaileyUpdated on March 13, 2019

What Are Archaea?

Archaea are a group of microscopic organisms that were discovered in the early 1970s. Like bacteria, they are single-celled prokaryotes. Archaeans were originally thought to be bacteria until DNA analysis showed that they are different organisms. In fact, they are so different that the discovery prompted scientists to come up with a new system for classifying life. There is still much about archaeans that is not known. What we do know is that many are extreme organisms that live and thrive under some of the most extreme conditions, such as extremely hot, acidic, or alkaline environments.https://5d4a57fc4a3dc09b42da820e3bb71dff.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Key Takeaways

  • Originally thought to be bacteria, Archaea are a separate group of microscopic organisms discovered in the 1970s. Archaeans are single-celled prokaryotes.
  • Archaeans are extreme organisms. They can survive and even thrive under some of the most difficult conditions on planet Earth like very hot, extremely acidic, or very alkaline environments.
  • Similar to bacteria, Archaeans have a number of different shapes. Cocci (round), bacilli (rod-shaped), and irregular are some examples.
  • Archaeans possess the typical prokaryotic cell anatomy that includes plasmid DNA, a cell wall, a cell membrane, a cytoplasmic area, and ribosomes. Some archaeans can also have flagella.

Archaea Cells

Archaeans are extremely small microbes that must be viewed under an electron microscope to identify their characteristics. Like bacteria, they come in a variety of shapes including cocci (round), bacilli (rod-shaped), and irregular shapes. Archaeans have a typical prokaryotic cell anatomy: plasmid DNAcell wallcell membranecytoplasm, and ribosomes. Some archaeans also have long, whip-like protrusions called flagella, which aid in movement.https://5d4a57fc4a3dc09b42da820e3bb71dff.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Archaea Domain

Organisms are now classified into three domains and six kingdoms. The domains include Eukaryota, Eubacteria, and Archaea. Under the archaea domain, there are three main divisions or phyla. They are: Crenarchaeota, Euryarchaeota, and Korarchaeota.


Crenarchaeota consist mostly of hyperthermophiles and thermoacidophiles. Hyperthermophilic microorganisms live in extremely hot or cold environments. Thermoacidophiles are microscopic organisms that live in extremely hot and acidic environments. Their habitats have a pH between 5 and 1. You would find these organisms in hydrothermal vents and hot springs.https://5d4a57fc4a3dc09b42da820e3bb71dff.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Crenarchaeota Species

Examples of Crenarchaeotans include:

  • Sulfolobus acidocaldarius – found near volcanic environments in hot, acidic springs containing sulfur.
  • Pyrolobus fumarii – live in temperatures between 90 and 113 degrees Celsius.


Euryarchaeota organisms consist mostly of extreme halophiles and methanogens. Extreme halophilic organisms live in salty habitats. They need salty environments to survive. You would find these organisms in salt lakes or areas where sea water has evaporated.
Methanogens require oxygen free (anaerobic) conditions in order to survive. They produce methane gas as a byproduct of metabolism. You would find these organisms in environments such as swamps, wetlands, ice lakes, the guts of animals (cow, deer, humans), and in sewage.

Euryarchaeota Species

Examples of Euryarchaeotans include:

  • Halobacterium – include several species of halophilic organisms that are found in salt lakes and high saline ocean environments.
  • Methanococcus – Methanococcus jannaschii was the first genetically sequenced Archaean. This methanogen lives near hydrothermal vents.
  • Methanococcoides burtonii – these psychrophilic (cold-loving) methanogens were discovered in Antarctica and can survive extremely cold temperatures.


Korarchaeota organisms are thought to be very primitive life forms. Little is currently known about the major characteristics of these organisms. We do know that they are thermophilic and have been found in hot springs and obsidian pools.

Archaea Phylogeny

Archaea are interesting organisms in that they have genes that are similar to both bacteria and eukaryotes. Phylogenetically speaking, archaea and bacteria are thought to have developed separately from a common ancestor. Eukaryotes are believed to have branched off from archaeans millions of years later. This suggests that archaeans are more closely related to eukayotes than bacteria.

Interesting Archaeans Facts

While Archaeans are very similar to bacteria, they are also much different. Unlike some types of bacteria, archaeans can not perform photosynthesis. Similarly, they cannot produce spores.

Archaeans are extremophiles. They can live in places where most other life forms cannot. They can be found in extremely high temperature environments as well as extremely low temperature environments.

Archaeans are a natural part of human microbiota. At present, pathogenic archaeans have not been identified. Scientists assume that they do not exist.

Bacteria: Friend or Foe?

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Helicobacter pylori
 These are multiple Helicobacter pylori which are Gram-negative, microaerophilic bacteria found in the stomach.Science Picture Co/Subjects / Getty Images


By Regina BaileyUpdated on June 24, 2018

Bacteria are all around us and most people only consider these prokaryotic organisms to be disease-causing parasites. While it is true that some bacteria are responsible for a large number of human diseases, others play a vital role in necessary human functions such as digestion.https://3d86556795da70dbf6dc8613e1d08598.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Bacteria also make it possible for certain elements such as carbon, nitrogen, and oxygen to be returned to the atmosphere. These bacteria ensure that the cycle of chemical exchange between organisms and their environment is continuous. Life as we know it would not exist without bacteria to decompose waste and dead organisms, thus playing a key role in the flow of energy in environmental food chains.https://3d86556795da70dbf6dc8613e1d08598.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Are Bacteria Friend or Foe?

The decision as to whether bacteria are friend or foe becomes more difficult when both the positive and negative aspects of the relationship between humans and bacteria are considered. There are three types of symbiotic relationships in which humans and bacteria coexist. The types of symbiosis are termed commensalism, mutualism, and parasitism.

Symbiotic Relationships

Commensalism is a relationship that is beneficial to the bacteria but does not help or harm the host. Most commensal bacteria reside on epithelial surfaces that come in contact with the external environment. They are commonly found on the skin, as well as in the respiratory tract and the gastrointestinal tract. Commensal bacteria acquire nutrients and a place to live and grow from their host. In some instances, commensal bacteria may become pathogenic and cause disease, or they may provide a benefit for the host.https://3d86556795da70dbf6dc8613e1d08598.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

In a mutualistic relationship, both the bacteria and the host benefit. For example, there are several kinds of bacteria that live on the skin and inside the mouth, nose, throat, and intestines of humans and animals. These bacteria receive a place to live and feed while keeping other harmful microbes from taking up residence. Bacteria in the digestive system assist in nutrient metabolism, vitamin production, and waste processing. They also aid in the host’s immune system response to pathogenic bacteria. Most of the bacteria that reside within humans are either mutual or commensal.

parasitic relationship is one in which the bacteria benefit while the host is harmed. Pathogenic parasites, which cause disease, do so by resisting the host’s defenses and growing at the expense of the host. These bacteria produce poisonous substances called endotoxins and exotoxins, which are responsible for the symptoms that occur with an illness. Disease-causing bacteria are responsible for a number of diseases including meningitis, pneumonia, tuberculosis, and several types of food-borne diseases.

Bacteria: Helpful or Harmful?

When all of the facts are considered, bacteria are more helpful than harmful. Humans have exploited bacteria for a wide variety of uses. Such uses include making cheese and butter, decomposing waste in sewage plants, and developing antibiotics. Scientists are even exploring ways for storing data on bacteria. Bacteria are extremely resilient and some are capable of living in the most extreme environments. Bacteria have demonstrated that they are able to survive without us, but we could not live without them.

Biology Prefixes and Suffixes: -troph or -trophy

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Thin Horses
Credit: Piccerella/E+/Getty Images


By Regina BaileyUpdated on January 21, 2020

The affixes (troph and -trophy) refer to nourishment, nutrient material, or the acquisition of nourishment. It is derived from the Greek trophos, which means one who nourishes or is nourished.https://b7004d263971222307ac15ec089e0249.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Words Ending In: (-troph)

  • Allotroph (allo – troph): Organisms that get their energy from food obtained from their respective environments are allotrophs.
  • Autotroph (auto-troph): an organism that is self-nourishing or capable of generating its own food. Autotrophs include plantsalgae, and some bacteria. Autotrophs are producers in food chains.
  • Auxotroph (auxo-troph): a strain of microorganism, such as bacteria, that has mutated and has nutritional requirements that differ from the parent strain.
  • Biotroph (bio – troph): Biotrophs are parasites. They do not kill their hosts as they establish a long-term infection as they get their energy from living cells.
  • Bradytroph (brady – troph): This term refers to an organism that experiences very slow growth without the presence of a particular substance.
  • Chemotroph (chemo-troph): an organism that obtains nutrients through chemosynthesis (oxidation of inorganic matter as a source of energy to produce organic matter). Most chemotrophs are bacteria and archaea living in very harsh environments. They are known as extremophiles and can thrive in extremely hot, acidic, cold, or salty habitats.
  • Electrotroph (electro – troph): Electrotrophs are organisms that can obtain their energy from an electric source.
  • Embryotroph (embryo-troph): all the nourishment supplied to mammalian embryos, such as the nourishment that comes from the mother through the placenta.
  • Hemotroph (hemo-troph): nutritive materials supplied to mammalian embryos through the blood supply of the mother.
  • Heterotroph (hetero-troph): an organism, such as an animal, that relies on organic substances for nourishment. These organisms are consumers in food chains.
  • Histotroph (histo-troph): nutritive materials, supplied to mammalian embryos, derived from maternal tissue other than blood.
  • Metatroph (meta-troph): an organism that requires complex nutritive sources of carbon and nitrogen for growth.
  • Necrotroph (necro – troph): Unlike biotrophs, necrotrophs are parasites that kill their host and survive on the dead remains.
  • Oligotroph (oligo – troph): Oligotrophs are organisms that can live in places with very few nutrients.
  • Phagotroph (phago-troph): an organism that obtains nutrients by phagocytosis (engulfing and digesting organic matter).
  • Phototroph (photo-troph): an organism that obtains nutrients by using light energy to convert inorganic matter into organic matter through photosynthesis.
  • Prototroph (proto-troph): a microorganism that has the same nutritional requirements as the parent strain.

Words Ending In: (-trophy)

  • Atrophy (a-trophy): a wasting away of an organ or tissue due to lack of nourishment or nerve damage. Atrophy can also be caused by poor circulation, inactivity or lack of exercise, and excessive cell apoptosis.
  • Axonotrophy (axono – trophy): This term refers to axon destruction due to a disease.
  • Cellulotrophy (cellulo – trophy): Cellulotrophy refers to the digestion of cellulose, an organic polymer.
  • Chemotrophy (chemo – trophy): This term refers to an organism making its energy by the oxidation of molecules.
  • Dystrophy (dys-trophy): a degenerative disorder resulting from inadequate nutrition. It also refers to a set of disorders characterized by muscle weakness and atrophy (muscular dystrophy).
  • Eutrophy (eu-trophy): refers to proper development due to healthy nutrition.
  • Hypertrophy (hyper-trophy): excessive growth in an organ or tissue due to increase in cell size, not in cell numbers.
  • Myotrophy (myo-trophy): nourishment of the muscles.
  • Oligotrophy (oligo-trophy): a state of poor nutrition. Often refers to an aquatic environment that lacks nutrients but has excess levels of dissolved oxygen.
  • Onychotrophy (onycho-trophy): nourishment of the nails.
  • Osmotrophy (osmo-trophy): the acquiring of nutrients through the uptake of organic compounds by osmosis.
  • Osteotrophy (osteo-trophy): nourishment of bone tissue.
  • Oxalotrophy (oxalo – trophy): This term refers to the metabolism of oxalates or oxalic acid by organisms.

Words Beginning With: (troph-)

  • Trophallaxis (tropho-allaxis): exchange of food between organisms of the same or different species. Trophallaxis typically occurs in insects between adults and larvae.
  • Trophobiosis (tropho-bi-osis): a symbiotic relationship in which one organism receives nourishment and the other protection. Trophobiosis is observed in relationships between some ant species and some aphids. The ants protect the aphid colony, while the aphids produce honeydew for the ants.
  • Trophoblast (tropho-blast): outer cell layer of a blastocyst that attaches the fertilized egg to the uterus and later develops into the placenta. The trophoblast provides nutrients for the developing embryo.
  • Trophocyte (tropho-cyte): any cell that provides nutrition.
  • Trophopathy (tropho-pathy):  a disease due to a disturbance of nutrition.

Differences Between Bacteria and Viruses

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Tongue Bacteria
Credit: Steve Gschmeissner/Getty Images


By Regina BaileyUpdated on July 18, 2019

Bacteria and viruses are both microscopic organisms that can cause disease in humans. While these microbes may have some characteristics in common, they are also very different. Bacteria are typically much larger than viruses and can be viewed under a light microscope. Viruses are about 1,000 times smaller than bacteria and are visible under an electron microscope. Bacteria are single-celled organisms that reproduce asexually independently of other organisms. Viruses require the aid of a living cell in order to reproduce.https://ba40ad2f6bdf8371ece6d0c6f5221b8b.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Where They Are Found

  • Bacteria: Bacteria live almost anywhere including within other organisms, on other organisms, and on inorganic surfaces. They infect eukaryotic organisms such as animals, plants, and fungi. Some bacteria are considered to be extremophiles and can survive in extremely harsh environments such as hydrothermal vents and in the stomachs of animals and humans.
  • Viruses: Much like bacteria, viruses can be found in almost any environment. They are pathogens that infect prokaryotic and eukaryotic organisms including animalsplants, bacteria, and archaeans. Viruses that infect extremophiles such as archaeans have genetic adaptations that enable them to survive harsh environmental conditions (hydrothermal vents, sulphuric waters, etc.). Viruses can persist on surfaces and on objects we use every day for varying lengths of time (from seconds to years) depending on the type of virus.

Bacterial and Viral Structure

  • Bacteria: Bacteria are prokaryotic cells that display all of the characteristics of living organisms. Bacterial cells contain organelles and DNA that are immersed within the cytoplasm and surrounded by a cell wall. These organelles perform vital functions that enable bacteria to obtain energy from the environment and to reproduce.
  • Viruses: Viruses are not considered cells but exist as particles of nucleic acid (DNA or RNA) encased within a protein shell. Some viruses have an additional membrane called an envelope that is composed of phospholipids and proteins obtained from the cell membrane of a previously infected host cell. This envelope helps the virus enter a new cell by fusion with the cell’s membrane and helps it exit by budding. non-enveloped viruses typically enter a cell by endocytosis and exit by exocytosis or cell lysis.Also known as virions, virus particles exist somewhere between living and non-living organisms. While they contain genetic material, they don’t have a cell wall or organelles necessary for energy production and reproduction. Viruses rely solely on a host for replication.

Size and Shape

  • Bacteria: Bacteria can be found in a variety of shapes and sizes. Common bacterial cell shapes include cocci (spherical), bacilli (rod-shaped), spiral, and vibrio. Bacteria typically range in size from 200-1000 nanometers (a nanometer is 1 billionth of a meter) in diameter. The largest bacterial cells are visible with the naked eye. Considered the world’s largest bacteria, Thiomargarita namibiensis can reach up to 750,000 nanometers (0.75 millimeters) in diameter.
  • Viruses: The size and shape of viruses are determined by the amount of nucleic acid and proteins they contain. Viruses typically have spherical (polyhedral), rod-shaped, or helically shaped capsids. Some viruses, such as bacteriophages, have complex shapes which include the addition of a protein tail attached to the capsid with tail fibers extending from the tail. Viruses are much smaller than bacteria. They generally range in size from 20-400 nanometers in diameter. The largest viruses known, the pandoraviruses, are about 1000 nanometers or a full micrometer in size.

How They Reproduce

  • Bacteria: Bacteria commonly reproduce asexually by a process known as binary fission. In this process, a single cell replicates and divides into two identical daughter cells. Under proper conditions, bacteria can experience exponential growth.
  • Viruses: Unlike bacteria, viruses can only replicate with the aid of a host cell. Since viruses don’t have the organelles necessary for the reproduction of viral components, they must use the host cell’s organelles to replicate. In viral replication, the virus injects its genetic material (DNA or RNA) into a cell. Viral genes are replicated and provide the instructions for the building of viral components. Once the components are assembled and the newly formed viruses mature, they break open the cell and move on to infect other cells.

Diseases Caused by Bacteria and Viruses

  • Bacteria: While most bacteria are harmless and some are even beneficial to humans, other bacteria are capable of causing disease. Pathogenic bacteria that cause disease produce toxins that destroy cells. They can cause food poisoning and other serious illnesses including meningitis, pneumonia, and tuberculosis. Bacterial infections can be treated with antibiotics, which are very effective at killing bacteria. Due to the overuse of antibiotics however, some bacteria (E.coli and MRSA) have gained resistance to them. Some have even become known as superbugs as they have gained resistance to multiple antibiotics. Vaccines are also useful in preventing the spread of bacterial diseases. The best way to protect yourself from bacteria and other germs is to properly wash and dry your hands often.
  • Viruses: Viruses are pathogens that cause a range of diseases including chickenpox, the flu, rabies, Ebola virus disease, Zika disease, and HIV/AIDS. Viruses can cause persistent infections in which they go dormant and can be reactivated at a later time. Some viruses can cause changes within host cells that result in the development of cancer. These cancer viruses are known to cause cancers such as liver cancer, cervical cancer, and Burkitt’s lymphoma. Antibiotics do not work against viruses. Treatment for viral infections typically involve medicines that treat the symptoms of an infection and not the virus itself. Antiviral drugs are used to treat some types of viral infections. Typically the host’s immune system is relied upon to fight off viruses. Vaccines can also be used to prevent viral infections.

Differences Between Bacteria and Viruses Chart

Cell TypeProkaryotic CellsAcellular (not cells)
Size200-1000 nanometers20-400 nanometers
StructureOrganelles and DNA within a cell wallDNA or RNA within a capsid, some have an envelope membrane
Cells They InfectAnimal, Plant, FungiAnimal, Plant, Protozoa, Fungi, Bacteria, Archaea
ReproductionBinary fissionRely on host cell
ExamplesE.coliSalmonella, Listeria, Mycobacteria, Staphylococcus, Bacillus anthracisInfluenza viruses, Chickenpox viruses, HIV, Polio virus, Ebola virus
Diseases CausedTuberculosis, Food poisoning, Flesh-eating disease, Meningococcal meningitis, AnthraxChickenpox, polio, flu, measles, rabies, AIDS
TreatmentAntibioticsAntiviral drugs

3 Types of Sexual Life Cycles

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 An egg cell undergoing mitosis.iLexx/Getty Images


By Heather ScovilleUpdated on February 15, 2019

One of the properties of life is the ability to reproduce to create offspring that can carry on the genetics of the parent or parents to the following generations. Living organisms can accomplish this by reproducing in one of two ways. Some species use asexual reproduction to make offspring, while others reproduce using sexual reproduction. While each mechanism has its pros and its cons, whether or not a parent needs a partner to reproduce or it can make offspring on its own are both valid ways to carry on the species.https://3d6457ec4a0e01938fafd218b8dcf85c.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Different kinds of eukaryotic organisms that undergo sexual reproduction have different types of sexual life cycles. These life cycles determine how the organism will not only make its offspring but also how the cells within the multicellular organism will reproduce themselves. The sexual life cycle determines how many sets of chromosomes each cell in the organism will have.

Diplontic Life Cycle

A diploid cell is a type of eukaryotic cell that has 2 sets of chromosomes. Usually, these sets are a genetic mixture of both the male and female parent. One set of the chromosomes comes from the mother and one set comes from the father. This allows a nice mixture of the genetics of both parents and increases diversity of traits in the gene pool for natural selection to work on.

In a diplontic life cycle, the majority of the organism’s life is spent with most of the cells in the body being diploid. The only cells that have half the number of chromosomes, or are haploid, are the gametes (sex cells). Most organisms that have a diplontic life cycle start from the fusion of two haploid gametes. One of the gametes comes from a female and the other from the male. This coming together of the sex cells creates a diploid cell called a zygote.

Since the diplontic life cycle keeps most of the body cells as diploid, mitosis can happen to split the zygote and continue splitting future generations of cells. Before mitosis can happen, the cell’s DNA is duplicated to make sure the daughter cells have two full sets of chromosomes that are identical to each other.https://3d6457ec4a0e01938fafd218b8dcf85c.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

The only haploid cells that happen during a diplontic life cycle are gametes. Therefore, mitosis cannot be used to make the gametes. Instead, the process of meiosis is what creates the haploid gametes from the diploid cells in the body. This ensures that the gametes will have only one set of chromosomes, so when they fuse again during sexual reproduction, the resulting zygote will have the two sets of chromosomes of a normal diploid cell.

Most animals, including humans, have a diplontic sexual life cycle.

Haplontic Life Cycle

Cells that spend the majority of their lives in a haploid phase are considered to have a haplontic sexual life cycle. In fact, organisms that have a haplontic life cycle are only composed of a diploid cell when they are zygotes. Just like in the diplontic life cycle, a haploid gamete from a female and a haploid gamete from a male will fuse to make a diploid zygote. However, that is the only diploid cell in the entire haplontic life cycle. 

The zygote undergoes meiosis at its first division to create daughter cells that have half the number of chromosomes compared to the zygote. After that division, all of the now haploid cells in the organism undergo mitosis in future cell divisions to create more haploid cells. This continues on for the organism’s entire life cycle. When it is time to sexually reproduce, the gametes are already haploid and can just fuse with another organism’s haploid gamete to form the zygote of the offspring.

Examples of organisms that live a haplontic sexual life cycle include fungi, some protists, and some plants.

Alternation of Generations

The final type of sexual life cycle is a kind of mix of the two previous types. Called alternation of generations, the organism spends about half of its life in a haplontic life cycle and the other half of its life in a diplontic life cycle. Like the haplontic and diplontic life cycles, organisms that have an alternation of generations sexual life cycle begin life as a diploid zygote formed from the fusion of haploid gametes from a male and a female.

The zygote can then either undergo mitosis and enter its diploid phase, or perform meiosis and become haploid cells. The resulting diploid cells are called sporophytes and the haploid cells are called gametophytes. The cells will continue to do mitosis and split in whichever phase they enter and create more cells for growth and repair. Gametophytes can then once again fuse to become a diploid zygote of the offspring.

Most plants live the alternation of generations sexual life cycle.

Laws of Thermodynamics as Related to Biology

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Energy and Thermodynamics
Mikael Häggström / Public Domain


By Regina BaileyUpdated on July 28, 2019

The laws of thermodynamics are important unifying principles of biology. These principles govern the chemical processes (metabolism) in all biological organisms. The First Law of Thermodynamics, also known ​as the law of conservation of energy, states that energy can neither be created nor destroyed. It may change from one form to another, but the energy in a closed system remains constant.https://53e43a3d13845828c2ed2dd737025b05.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

The Second Law of Thermodynamics states that when energy is transferred, there will be less energy available at the end of the transfer process than at the beginning. Due to entropy, which is the measure of disorder in a closed system, all of the available energy will not be useful to the organism. Entropy increases as energy is transferred.https://53e43a3d13845828c2ed2dd737025b05.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

In addition to the laws of thermodynamics, the cell theory, gene theory, evolution, and homeostasis form the basic principles that are the foundation for the study of life.

First Law of Thermodynamics in Biological Systems

All biological organisms require energy to survive. In a closed system, such as the universe, this energy is not consumed but transformed from one form to another. Cells, for example, perform a number of important processes. These processes require energy. In photosynthesis, the energy is supplied by the sun. Light energy is absorbed by cells in plant leaves and converted to chemical energy. The chemical energy is stored in the form of glucose, which is used to form complex carbohydrates necessary to build plant mass.

The energy stored in glucose can also be released through cellular respiration. This process allows plant and animal organisms to access the energy stored in carbohydrates, lipids, and other macromolecules through the production of ATP. This energy is needed to perform cell functions such as DNA replication, mitosis, meiosis, cell movement, endocytosis, exocytosis, and apoptosis.

Second Law of Thermodynamics in Biological Systems

As with other biological processes, the transfer of energy is not 100 percent efficient. In photosynthesis, for example, not all of the light energy is absorbed by the plant. Some energy is reflected and some is lost as heat. The loss of energy to the surrounding environment results in an increase of disorder or entropy. Unlike plants and other photosynthetic organisms, animals cannot generate energy directly from the sunlight. They must consume plants or other animal organisms for energy.

The higher up an organism is on the food chain, the less available energy it receives from its food sources. Much of this energy is lost during metabolic processes performed by the producers and primary consumers that are eaten. Therefore, much less energy is available for organisms at higher trophic levels. (Trophic levels are groups that help ecologists understand the specific role of all living things in the ecosystem.) The lower the available energy, the less number of organisms can be supported. This is why there are more producers than consumers in an ecosystem.

Living systems require constant energy input to maintain their highly ordered state. Cells, for example, are highly ordered and have low entropy. In the process of maintaining this order, some energy is lost to the surroundings or transformed. So while cells are ordered, the processes performed to maintain that order result in an increase in entropy in the cell’s/organism’s surroundings. The transfer of energy causes entropy in the universe to increase.

Frequently Asked Biology Questions and Answers

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 The cell nuclei contain the genetic material chromatin (red). The proteins making up the cells cytoskeleton have been stained with different colors: actin is blue and microtubules are yellow.DR Torsten Wittmann/Science Photo Library/Getty Image


By Regina BaileyUpdated on July 10, 2019

Biology is a wondrous science that inspires us to discover more about the world around us. While science may not have the answers to every question, some biology questions are answerable. Have you ever wondered why DNA is twisted or why some sounds make your skin crawl? Discover answers to these and other intriguing biology questions.

Why Is DNA Twisted?

DNA Double Helix
KTSDESIGN/Getty Images

DNA is known for its familiar twisted shape. This shape is often described as a spiral staircase or twisted ladder. DNA is a nucleic acid with three main components: nitrogenous bases, deoxyribose sugars, and phosphate molecules. Interactions between water and the molecules that compose DNA cause this nucleic acid to take on a twisted shape. This shape aids in the packing of DNA into chromatin fibers, which condense to form chromosomes. The helical shape of DNA also makes DNA replication and protein synthesis possible. When necessary, the double helix unwinds and opens to allow DNA to be copied.

Why Do Certain Sounds Make Your Skin Crawl?

Nails scraping against a chalkboard
 Nails scraping against a chalkboard is one of ten most hated sounds. Tamara Staples/Stone/Getty Images

Nails on a chalkboard, squealing brakes, or a crying baby are all sounds that can make one’s skin crawl. Why does this happen? The answer involves how the brain processes sound. When we detect a sound, sound waves travel to our ears and the sound energy is converted to nerve impulses. These impulses travel to the auditory cortex of the brain’s temporal lobes for processing. Another brain structure, the amygdala, heightens our perception of the sound and associates it with a particular emotion, such as fear or unpleasantness. These emotions can elicit a physical response to certain sounds, such as goose bumps or a sensation that something is crawling over your skin.

What Are the Differences Between Eukaryotic and Prokaryotic Cells?

Pseudomonas Bacteria
 Pseudomonas Bacteria. SCIEPRO/Science Photo Library/Getty Images

The primary characteristic that differentiates eukaryotic cells from prokaryotic cells is the cell nucleus. Eukaryotic cells have a nucleus that is surrounded by a membrane, which separates the DNA within from the cytoplasm and other organelles. Prokaryotic cells do not have a true nucleus in that the nucleus is not surrounded by a membrane. Prokaryotic DNA is located in an area of the cytoplasm called the nucleoid region. Prokaryotic cells are typically much smaller and less complex than eukaryotic cells. Examples of eukaryotic organisms include animals, plants, fungi and protists (ex. algae).

How Are Fingerprints Formed?

Dactylogram or Fingerprint
Andrey Prokhorov/E+/Getty Image

Fingerprints are patterns of ridges that form on our fingers, palms, toes, and feet. Fingerprints are unique, even among identical twins. They are formed while we are in our mother’s womb and are influenced by several factors. These factors include genetic makeup, position in the womb, amniotic fluid flow, and umbilical cord length. Fingerprints are formed in the innermost layer of the epidermis known as the basal cell layer. Rapid cell growth in the basal cell layer causes this layer to fold and form various patterns.

What Are the Differences Between Bacteria and Viruses?

Influenza Virus Particle
 Influenza virus particle. CDC/Frederick Murphy

While both bacteria and viruses are capable of making us sick, they are very different microbes. Bacteria are living organisms that produce energy and are capable of independent reproduction. Viruses are not cells but particles of DNA or RNA encased within a protective shell. They do not possess all of the characteristics of living organisms. Viruses must rely on other organisms in order to reproduce because they do not possess the organelles needed to replicate. Bacteria are typically larger than viruses and susceptible to antibiotics. Antibiotics do not work against viruses and viral infections.https://77f7c054a23271e3fa804e5a96b8e2d1.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Why Do Women Typically Live Longer Than Men?

3 generations of women
 Women on average live anywhere from 5 to 7 years longer than men. B2M Productions/Digital Vision/Getty Images

In almost every culture, women usually outlive men. While several factors can influence the life expectancy differences between men and women, genetic makeup is considered to be the major reason women live longer than men. Mitochondrial DNA mutations cause males to age faster than females. Since mitochondrial DNA is only inherited from mothers, mutations that occur in female mitochondrial genes are monitored to filter out dangerous mutations. Male mitochondrial genes are not monitored so the mutations accumulate over time.https://77f7c054a23271e3fa804e5a96b8e2d1.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

What Are the Differences Between Plant and Animal Cells?

Animal Cell vs Plant Cell
Encyclopaedia Britannica/UIG/Getty Images

Animal cells and plant cells are both eukaryotic cells with a number of common characteristics. These cells also differ in a number of characteristics such as size, shape, energy storage, growth, and organelles. Structures found in plant cells and not animal cells include a cell wall, plastids, and plasmodesmata. Centrioles and lysosomes are structures that are found in animal cells but not usually in plant cells. While plants are capable of generating their own food through photosynthesis, animals must obtain nutrition through ingestion or absorption.https://77f7c054a23271e3fa804e5a96b8e2d1.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Is the 5-second Rule True or a Myth?

Baby With Food on Floor
 Is it okay to apply the 5-second rule to foods that fall on the floor? Studies suggest that there is some truth to the 5-second rule. David Woolley/Digital Vision/Getty Images

The 5-second rule is based on the theory that food that has been dropped on the floor for a brief period of time does not pick up many germs and is safe to eat. This theory is somewhat true in that the less time food is in contact with a surface, the fewer bacteria are transferred to the food. Several factors play a role in the level of contamination that may occur once food has been dropped on the floor or another surface. These factors include the texture of the food (soft, sticky, etc.) and the type of surface (tile, carpet, etc.) involved. It is always best to avoid eating food that has a high risk of contamination, such as food that has been dropped in the trash.

What Are the Differences Between Mitosis and Meiosis?

Dividing Cell in Mitosis
 Dividing Cell in Mitosis. Dr. Lothar Schermelleh/Science Photo Library/Getty Images

Mitosis and meiosis are cell division processes that involve the division of a diploid cell. Mitosis is the process by which somatic cells (body cells) reproduce. Two identical daughter cells are produced as a result of mitosis. Meiosis is the process by which gametes (sex cells) are formed. This two-part cell division process produces four daughter cells that are haploid. In sexual reproduction, the haploid sex cells unite during fertilization to form a diploid cell.

What Happens When Lightning Strikes You?

Lightning Strike
 A cloud-to-ground lightning strike originating from higher based cloud structure. Lightning penetrates a low level cloud before reaching earth. NOAA Photo Library, NOAA Central Library; OAR/ERL/National Severe Storms Laboratory (NSSL)

Lightning is a powerful force that can cause serious injury to those that are unfortunate enough to be hit by it. There are five ways in which individuals may be hit by lightning. These types of strikes include a direct strike, side flash, ground current strike, conduction strike, and a streamer strike. Some of these strikes are more serious than others but all involve electrical current traveling through the body. This current moves over the skin or through the cardiovascular system and nervous system causing serious damage to vital organs.

What Is the Purpose of Bodily Functions?

Baby Yawning
 Baby Yawning.  Multi-bits/The Image Bank/Getty Images

Have you ever wondered why we yawn, burp, sneeze, or cough? Some bodily functions are the result of voluntary actions controlled by the individual, while others are involuntary and not under the control of the individual. Yawning, for example, is a reflex response that occurs when a person is tired or bored. Though the reasons for yawning are not fully understood, studies indicate that it helps to cool the brain.

What Are the Different Types of Plant Growth?

Germinating Seed
 The main stages in the germination of a plant seed. In the third image, the root grows downwards in response to gravity, while in the fourth image the embryonic shoot (plumule) grows up against gravity. Power and Syred/Science Photo Library/Getty Images

Have you ever noticed how plants grow toward different types of stimuli? Growth of a plant in the direction of a stimulus is called plant tropism. Some of these stimuli include light, gravity, water, and touch. Other types of plant tropisms include growth in the direction of chemical signals (chemotropism) and growth in response to heat or temperature changes (thermotropism).

12 Interesting Facts About Blood

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Red Blood Cells in Bloodstream
Science Picture Co/Getty Images


By Regina BaileyUpdated on June 21, 2019

Blood is the life-giving fluid that delivers oxygen to the cells of the body. It is a specialized type of connective tissue that consists of red blood cells, platelets, and white blood cells suspended in a liquid plasma matrix.

These are the basics, but there are many more surprising facts as well; for example, blood accounts for about 8 percent of your body weight and it contains trace amounts of gold.

Intrigued yet? Read on below for 12 more fascinating facts.01of 12

Not All Blood Is Red

Blood on a finger
Jonathan Knowles/Stone/Getty Images

While humans have red colored blood, other organisms have blood of varying colors. Crustaceans, spiders, squid, octopuses, and some arthropods have blue blood. Some types of worms and leeches have green blood. Some species of marine worms have violet blood. Insects, including beetles and butterflies, have colorless or pale-yellowish blood. The color of blood is determined by the type of respiratory pigment used to transport oxygen via the circulatory system to cells. The respiratory pigment in humans is a protein called hemoglobin found in red blood cells.02of 12

Your Body Contains About a Gallon of Blood

Human heart anatomy, computer artwork.

The adult human body contains approximately 1.325 gallons of blood. Blood makes up about 7 to 8 percent of a person’s total body weight.03of 12

Blood Consists Mostly of Plasma

Plasma cells, artwork

Blood circulating in your body is composed of about 55 percent plasma, 40 percent red blood cells, 4 percent platelets, and 1 percent white blood cells. Of the white blood cells in blood circulation, neutrophils are the most abundant.04of 12

White Blood Cells Are Necessary for Pregnancy

Pregnant woman standing in the bedroom
Michael Poehlman/Getty Images

It is well known that white blood cells are important for a healthy immune system. What is less known is that certain white blood cells called macrophages are necessary for pregnancy to occur. Macrophages are prevalent in reproductive system tissues. Macrophages assist in the development of blood vessel networks in the ovary, which is vital for the production of the hormone progesterone. Progesterone plays a critical part in the implantation of an embryo in the uterus. Low macrophage numbers result in reduced progesterone levels and inadequate embryo implantation.05of 12

There’s Gold in Your Blood

liquid gold
 Seyfi Karagunduz/EyeEm/Getty Images 

Human blood contains metals atoms including iron, chromium, manganese, zinc, lead, and copper. You may also be surprised to know that blood contains small amounts of gold. The human body has about 0.2 milligrams of gold that is mostly found in the blood.06of 12

Blood Cells Originate From Stem Cells

stem cells
DAVID MACK/Getty Images 

In humans, all blood cells originate from hematopoietic stem cells. About 95 percent of the body’s blood cells are produced in the bone marrow. In an adult, most of the bone marrow is concentrated in the breastbone and in the bones of the spine and pelvis. Several other organs help to regulate the production of blood cells. These include the liver and lymphatic system structures such as the lymph nodesspleen, and thymus.07of 12

Blood Cells Have Different Life Spans

Red blood cells and platelets in circulation
Science Photo Library – SCIEPRO/Brand X Pictures/Getty Images

Matured human blood cells have varying life cycles. Red blood cells circulate in the body for about 4 months, platelets for about 9 days, and white blood cells range from a few hours to several days.08of 12

Red Blood Cells Have No Nucleus

Red Blood Cells

Unlike other types of cells in the body, mature red blood cells do not contain a nucleusmitochondria, or ribosomes. The absence of these cell structures leaves room for the hundreds of millions of hemoglobin molecules found in red blood cells.09of 12

Blood Proteins Protect Against Carbon Monoxide Poisoning

carbon monoxide detector
BanksPhotos / Getty Images

Carbon monoxide (CO) gas is colorless, odorless, tasteless and toxic. It is not only produced by fuel-burning devices but is also produced as a by-product of cellular processes. If carbon monoxide is produced naturally during normal cell functions, why aren’t organisms poisoned by it? Because CO is produced in much lower concentrations than seen in CO poisoning, cells are protected from its toxic effects. CO binds to proteins in the body known as hemoproteins. Hemoglobin found in blood and cytochromes found in mitochondria are examples of hemoproteins. When CO binds to hemoglobin in red blood cells, it prevents oxygen from binding to the protein molecule leading to disruptions in vital cell processes such as cellular respiration. At low CO concentrations, hemoproteins change their structure preventing CO from successfully binding to them. Without this structural change, CO would bind to the hemoprotein up to a million times more tightly.10of 12

Capillaries Spit Out Blockages in Blood

Capillary network
shulz/Getty Images 

Capillaries in the brain can expel obstructive debris. This debris may consist of cholesterol, calcium plaque, or clots in the blood. Cells within the capillary grow around and enclose the debris. The capillary wall then opens up and the obstruction is forced out of the blood vessel into the surrounding tissue. This process slows down with age and is thought to be a factor in cognitive decline that occurs as we age. If the obstruction is not completely removed from the blood vessel, it can cause oxygen deprivation and nerve damage.11of 12

UV Rays Reduce Blood Pressure

Sun in the blue sky with lensflare
tomch / Getty Images

Exposing a person’s skin to the sun’s rays reduces blood pressure by causing levels of nitric oxide to rise in the blood. Nitric oxide helps to regulate blood pressure by reducing blood vessel tone. This reduction in blood pressure could cut the risks of developing heart disease or stroke. While prolonged exposure to the sun could potentially cause skin cancer, scientists believe that very limited exposure to the sun could increase the risks of developing cardiovascular disease and related conditions.12of 12

Blood Types Vary by Population

The most common blood type in the United States is O positive. The least common is AB negative. Blood type distributions vary by population. The most common blood type in Japan is A positive.

How to Format a Biology Lab Report

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Focused high school student microscope listening science classroom
Hero Images / Getty Images


By Regina BaileyUpdated on May 05, 2019

If you are taking a general biology course or AP Biology, at some point you will have to do biology lab experiments. This means that you will also have to complete biology lab reports.https://71a9f46f4a6c97c2ccb962261fd9f923.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

The purpose of writing a lab report is to determine how well you performed your experiment, how much you understood about what happened during the experimentation process, and how well you can convey that information in an organized fashion.

Lab Report Format

A good lab report format includes six main sections:https://71a9f46f4a6c97c2ccb962261fd9f923.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

  • Title
  • Introduction
  • Materials and Methods
  • Results
  • Conclusion
  • References

Keep in mind that individual instructors may have a specific format that they require you to follow. Please be sure to consult your teacher about the specifics of what to include in your lab report.

Title: The title states the focus of your experiment. The title should be to the point, descriptive, accurate, and concise (ten words or less). If your instructor requires a separate title page, include the title followed by the name(s) of the project participant(s), class title, date, and instructors name. If a title page is required, consult your instructor about the specific format for the page.https://71a9f46f4a6c97c2ccb962261fd9f923.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Introduction: The introduction of a lab report states the purpose of your experiment. Your hypothesis should be included in the introduction, as well as a brief statement about how you intend to test your hypothesis.

To be sure that you have a good understanding of your experiment, some educators suggest writing the introduction after you have completed the methods and materials, results, and conclusion sections of your lab report.

Methods and Materials: This section of your lab report involves producing a written description of the materials used and the methods involved in performing your experiment. You should not just record a list of materials, but indicate when and how they were used during the process of completing your experiment.

The information you include should not be overly detailed but should include enough detail so that someone else could perform the experiment by following your instructions.

Results: The results section should include all tabulated data from observations during your experiment. This includes charts, tables, graphs, and any other illustrations of data you have collected. You should also include a written summary of the information in your charts, tables, and/or other illustrations. Any patterns or trends observed in your experiment or indicated in your illustrations should be noted as well.

Discussion and Conclusion: This section is where you summarize what happened in your experiment. You will want to fully discuss and interpret the information. What did you learn? What were your results? Was your hypothesis correct, why or why not? Were there any errors? If there is anything about your experiment that you think could be improved upon, provide suggestions for doing so.

Citation/References: All references used should be included at the end of your lab report. That includes any books, articles, lab manuals, etc. that you used when writing your report.

Example APA citation formats for referencing materials from different sources are listed below.

  • Book
    Name of author or authors (last name, first initial, middle initial)
    Year of publication
    Title of book
    Edition (if more than one)
    Place where published (city, state) followed by a colon
    Publisher nameFor example: Smith, J. B. (2005). Science of Life. 2nd Edition. New York, NY: Thompson Brooks.
  • Journal
    Name of author or authors (last name, first initial, middle initial)
    Year of publication
    Article title
    Journal title
    Volume followed by issue number (issue number is in parenthesis)
    Page numbersFor example: Jones, R. B. & Collins, K. (2002). Creatures of the desert. National Geographic. 101(3), 235-248.

Your instructor may require that you follow a specific citation format. Be sure to consult your teacher concerning the citation format that you should follow.

What Is an Abstract?

Some instructors also require that you include an abstract in your lab report. An abstract is a concise summary of your experiment. It should include information about the purpose of the experiment, the problem being addressed, the methods used for solving the problem, overall results from the experiment, and the conclusion drawn from your experiment.

The abstract typically comes at the beginning of the lab report, after the title, but should not be composed until your written report is completed. View a sample lab report template.

Do Your Own Work

Remember that lab reports are individual assignments. You may have a lab partner, but the work that you do and report on should be your own. Since you may see this material again on an exam, it is best that you know it for yourself. Always give credit where credit is due on your report. You don’t want to plagiarize the work of others. That means you should properly acknowledge the statements or ideas of others in your report.

Biology Prefixes and Suffixes: Ex- or Exo-

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Cicada Exoskeleton
Kaori Kurita / Getty Images


By Regina BaileyUpdated on February 21, 2019

The prefix (ex- or exo-) means out of, away from, outer, external, outside, or exterior. It is derived from the Greek exo meaning “out of” or external.

Words Beginning With: (Ex- or Exo-)

Excoriation (ex-coriation): An excoriation is a scratch or abrasion on the outer layer or surface of the skin. Some individuals suffer from excoriation disorder, a type of obsessive-compulsive disorder, in which they persistently pick at or scratch their skin causing sores.

Exergonic (ex-ergonic): This term describes a biochemical process that involves the release of energy into the surroundings. These types of reactions happen spontaneously. Cellular respiration is an example of an exergonic reaction that happens within our cells.

Exfoliation (ex-foliation): Exfoliation is the process of shedding cells or scales from the outer tissue surface.

Exobiology (exo-biology): The study of and search for life in the universe outside of Earth is known as exobiology.

Exocarp (exo-carp): The outermost layer of the wall of a ripened fruit is the exocarp. This outer protective layer can be a hard shell (coconut), a peel (orange), or skin (peach).

Exocrine (exo-crine): The term exocrine refers to the secretion of a substance externally. It also refers to glands that secrete hormones through ducts that lead to epithelium rather than directly into the blood. Examples include sweat and salivary glands.

Exocytosis (exo-cytosis): Exocytosis is a process by which substances are exported from a cell. The substance is contained within a vesicle that fuses with the outer cell membrane. The substance is thereby exported to the exterior of the cell. Hormones and proteins are secreted in this manner.

Exoderm (exo-derm): The exoderm is the outer germ layer of a developing embryo, which forms skin and nervous tissue.

Exogamy (exo-gamy): Exogamy is the union of gametes from organisms that are not closely related, as in cross pollination. It also means to marry outside of ones culture or social unit.

Exogen (exo-gen): An exogen is a flowering plant that grows by increasing layers on its exterior tissue.

Exons (ex-on): Exons are sections of DNA that code for the messenger RNA (mRNA) molecule produced during protein synthesis. During DNA transcription, a copy of the DNA message is created in the form of mRNA with both coding sections (exons) and non-coding sections (introns). The final mRNA product is generated when non-coding regions are spliced from the molecule and exons are joined together.

Exonuclease (exo-nuclease): An exonuclease is an enzyme that digests DNA and RNA by cutting out a single nucleotide at a time from the end of the molecules. This enzyme is important for DNA repair and genetic recombination.

Exophoria (exo-phoria): Exophoria is the tendency for one or both eyes to move outward. It is a type of eye misalignment or strabismus that can cause double vision, eye strain, blurred vision, and headaches.

Exophthalmos (ex-ophthalmos): An abnormal outward bulging of the eyeballs is called exophthalmos. It is commonly associated with an overactive thyroid gland and Graves’ disease.

Exoskeleton (exo-skeleton): An exoskeleton is the hard outer structure that provides support or protection for an organism; outer shell. Arthropods (including insects and spiders) as well as other invertebrate animals have exoskeletons.

Exosmosis (ex-osmosis): Exosmosis is a type of osmosis where fluid moves from the inside of a cell, across a semi-permeable membrane, to an external medium. The fluid moves from an area of high solute concentration to an area of lower solute concentration.

Exospore (exo-spore): The outer layer of an algal or fungal spore is called the exospore. This term also refers to a spore that is separated from the spore-bearing apparatus (sporophore) of fungi.

Exostosis (ex-ostosis): An exostosis is a common type of benign tumor that extends from the exterior surface of a bone. These outgrowths may occur on any bone and are called osteochondromas when they are covered with cartilage.

Exotoxin (exo-toxin): An exotoxin is a poisonous substance produced by some bacteria that is excreted into their surrounding environment. Exotoxins cause serious damage to host cells and can cause disease in humans. Bacteria that produce exotoxins include Corynebacterium diphtheriae (diphtheria), Clostridium tetani (tetanus), Enterotoxigenic E. coll (severe diarrhea), and Staphylococcus aureus (toxic shock syndrome).

Exothermic (exo-thermic): This term describes a type of chemical reaction in which heat is released. Examples of exothermic reactions include fuel combustion and burning.

7 Facts About Bacteriophages

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T4 Bacteriophage
 This is a T4 bacteriophage virus. The structure at top is the head, which contains DNA inside a protein coat. Attached to this is the tail, consisting of a tube-like sheath and tail fibres (at bottom). The virus attaches itself to the host bacteria cell wall by its tail fibres; the sheath then contracts, injecting the contents of the head (DNA) into the host. PASIEKA/Science Photo Library/Getty Images


By Regina BaileyUpdated on September 05, 2018

Bacteriophages are “bacteria eaters” in that they are viruses that infect and destroy bacteria. Sometimes called phages, these microscopic organisms are ubiquitous in nature. In addition to infecting bacteria, bacteriophages also infect other microscopic prokaryotes known as archaea. This infection is specific to a specific species of bacteria or archaea. A phage that infects E. coli for instance, will not infect anthrax bacteria. Since bacteriophages do not infect human cells, they have been used in medical therapies to treat bacterial diseases.

Bacteriophages have three main structure types.

Since bacteriophages are viruses, they consist of a nucleic acid (DNA or RNA) enclosed within a protein shell or capsid. A bacteriophage may also have a protein tail attached to the capsid with tail fibers extending from the tail. The tail fibers help the phage attach to its host and the tail helps to inject the viral genes into the host. A bacteriophage may exist as:

  1. viral genes in a capsid head with no tail
  2. viral genes in a capsid head with a tail
  3. a filamentous or rod-shaped capsid with circular single-stranded DNA.

Bacteriophages pack their genome

How do viruses fit their voluminous genetic material into their capsids? RNA bacteriophages, plant viruses, and animal viruses have a self-folding mechanism that enables the viral genome to fit within the capsid container. It appears that only viral RNA genome have this self-folding mechanism. DNA viruses fit their genome into the capsid with the help of special enzymes known as packing enzymes.

Bacteriophages have two life cycles

Bacteriophages are capable of reproducing by either the lysogenic or lytic life cycles. The lysogenic cycle is also known as the temperate cycle because the host is not killed. The virus injects its genes into the bacterium and the viral genes are inserted into the bacterial chromosome. In the bacteriophage lytic cycle, the virus replicates within the host. The host is killed when the newly replicated viruses break open or lyse the host cell and are released.

Bacteriophages transfer genes between bacteria

Bacteriophages help to transfer genes between bacteria by means of genetic recombination. This type of gene transfer is known as transduction. Transduction can be accomplished through either the lytic or lysogenic cycle. In the lytic cycle, for example, the phage injects its DNA into a bacterium and enzymes separate the bacterial DNA into pieces. The phage genes direct the bacterium to produce more viral genes and viral components (capsids, tail, etc.). As the new viruses begin to assemble, bacterial DNA may inadvertently become enclosed within a viral capsid. In this case, the phage possesses bacterial DNA instead of viral DNA. When this phage infects another bacterium, it injects the DNA from the previous bacterium into the host cell. The donor bacterial DNA then may become inserted into the genome of the newly infected bacterium by recombination. As a result, the genes from one bacterium are transferred to another.

Bacteriophages can make bacteria harmful to humans

Bacteriophages play a role in human disease by turning some harmless bacteria into agents of disease. Some bacteria species including E. coliStreptococcus pyogenes (causes flesh-eating disease), Vibrio cholerae (causes cholera), and Shigella (causes dysentery) become harmful when genes that produce toxic substances are transferred to them via bacteriophages. These bacteria are then able to infect humans and cause food poisoning and other deadly diseases.

Bacteriophages are being used to target superbugs

Scientists have isolated bacteriophages that destroy the superbug Clostridium difficile (C. diff)C. diff typically affects the digestive system causing diarrhea and colitis. Treating this type of infection with bacteriophages provides a way to preserve the good gut bacteria while destroying only the C. diff germs. Bacteriophages are seen as a good alternative to antibiotics. Due to antibiotic overuse, resistant strains of bacteria are becoming more common. Bacteriophages are also being used to destroy other superbugs including drug-resistant E. coli and MRSA.

Bacteriophages play a significant role in the world’s carbon cycle

Bacteriophages are the most abundant virus in the ocean. Phages known as Pelagiphages infect and destroy SAR11 bacteria. These bacteria convert dissolved carbon molecules into carbon dioxide and influence the amount of available atmospheric carbon. Pelagiphages play an important role in the carbon cycle by destroying SAR11 bacteria, which proliferate at a high rate and are very good at adapting to avoid infection. Pelagiphages keep SAR11 bacteria numbers in check, ensuring that there is not an overabundance of global carbon dioxide production.

Peri Prefix Meaning in Biology

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Tree Bark Split
 Periderm or bark is a secondary tissue layer that surrounds and protects underlying layers in some plants.lynn.h.armstrong photography//Getty Images


By Regina BaileyUpdated on March 21, 2019

The prefix (peri-) means around, near, surrounding, covering, or enclosing. It is derived from the Greek peri for about, near, or around.

Words That Begin With Peri

Perianth (peri-anth): The outer part of a flower that encloses its reproductive parts is called the perianth. The perianth of a flower includes the sepals and petals in angiosperms.

Pericardium (peri-cardium): The pericardium is the membranous sac that surrounds and protects the heart. This three-layered membrane serves to keep the heart in place in the chest cavity and prevents over-expansion of the heart. Pericardial fluid, which is located between the middle pericardial layer (parietal pericardium) and the innermost pericardial layer (visceral pericardium), helps to reduce friction between pericardial layers.

Perichondrium (peri-chondrium): The layer of fibrous connective tissue that surrounds cartilage, excluding cartilage at the end of joints, is called perichondrium. This tissue covers cartilage in structures of the respiratory system (trachea, larynx, nose, and epiglottis), as well as cartilage of the ribs, outer ear, and auditory tubes.

Pericranium (peri-cranium): The pericranium is a membrane that covers the outer surface of the skull. Also called the periosteum, it is the innermost layer of the scalp that covers bone surfaces except at the joints.

Pericycle (peri-cycle): Pericycle is plant tissue that surrounds vascular tissue in roots. It initiates the development of lateral roots and is also involved in secondary root growth.

Periderm (peri-derm): The outer protective plant tissue layer that surrounds roots and stems is the periderm or bark. The periderm replaces the epidermis in plants that undergo secondary growth. Layers composing the periderm include cork, cork cambium, and phelloderm.

Peridium (peri-dium): The outer layer that covers the spore-bearing structure in many fungi is called the peridium. Depending on the fungal species, the peridium may be thin or thick with between one and two layers.

Perigee (peri-gee): The perigee is the point in the orbit of a body (moon or satellite) around the Earth where it is nearest to the center of the Earth. The orbiting body travels faster at perigee than at any other point in its orbit.

Perikaryon (peri-karyon): Also known as cytoplasm, the perikaryon is all of the contents of a cell surrounding but excluding the nucleus. This term also refers to the cell body of a neuron, excluding the axons and dendrites.

Perihelion (peri-helion): The point in the orbit of a body (planet or comet) around the sun where it comes closest to the sun is called the perihelion.

Perilymph (peri-lymph): Perilymph is the fluid between the membranous labyrinth and bony labyrinth of the inner ear.

Perimysium (peri-mysium): The layer of connective tissue that wraps skeletal muscle fibers into bundles is called perimysium.

Perinatal (peri-natal): Perinatal refers to the time period occurring around the time of birth. This period spans from about five months before birth to one month after birth.

Perineum (peri-neum): The perineum is the area of the body located between the anus and genital organs. This region spans from the pubic arch to the tail bone.

Periodontal (peri-odontal): This term literally means around the tooth and is used to denote tissues that surround and support teeth. Periodontal disease, for example, is a disease of the gums that can range from minor gum inflammation to serious tissue damage and tooth loss.

Periosteum (peri-osteum): The periosteum is a dual-layered membrane that covers the outer surface of bones. The outer layer of the periosteum is dense connective tissue formed from collagen. The inner layer contains bone-producing cells called osteoblasts.

Peristalsis (peri-stalsis): Peristalsis is the coordinated contraction of smooth muscle around substances within a tube that moves the contents along the tube. Peristalsis occurs in the digestive tract and in tubular structures such as the ureters.

Peristome (peri-stome): In zoology, the peristome is a membrane or structure that surrounds the mouth in some invertebrates. In botany, peristome refers to small appendages (resembling teeth) that surround the opening of a capsule in mosses.

Peritoneum (peri-toneum): The dual-layered membrane lining of the abdomen that encases abdominal organs is known as the peritoneum. The parietal peritoneum lines the abdominal wall and the visceral peritoneum covers the abdominal organs.

Peritubular (peri-tubular): This term describes a position that is adjacent to or surrounds a tubule. For example, the peritubular capillaries are tiny blood vessels that are positioned around nephrons in the kidneys.

Levels of Taxonomy Used in Biology

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Evolution of life
De Agostini Picture Library / Getty Images


By Heather ScovilleUpdated on July 25, 2019

Taxonomy is the practice of categorizing and naming of species. The official “scientific name” of an organism consists of its Genus and its Species Identifier in a naming system called binomial nomenclature.

The Work of Carolus Linnaeus

The current taxonomic system gets its roots from the work of Carolus Linnaeus in the early 1700s. Before Linnaeus set up the rules of the two-word naming system, species had long and unwieldy Latin polynomials that were inconsistent and inconvenient for scientists when communicating with each other or even the public.

While Linnaeus’s original system had many fewer levels than the modern system has today, it was still an excellent place to start to organize all of life into similar categories for easier classification. He used the structure and function of body parts, mostly, to classify the organisms. Thanks to advances in technology and understanding the evolutionary relationships among species, we have been able to update the practice to get the most accurate classification system possible.

The Taxonomic Classification System

The modern taxonomic classification system has eight main levels (from most inclusive to most exclusive): Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species Identifier. Every different species has a unique species identifier and the more closely a species is related to it on the evolutionary tree of life, it will be included in a more inclusive group with the species being classified.

(Note: An easier way to remember the order of these levels is to use a mnemonic device to remember the first letter of each word in order. The one we use is “Do Keep Pond Clean Or Fish Get Sick“)


A domain is the most inclusive of the levels (meaning it has the most number of individuals in the group). Domains are used to distinguish between the cell types and, in the case of prokaryotes, where they are found and what the cell walls are made of. The current system recognizes three domains: Bacteria, Archaea, and Eukarya.


Domains are further broken into Kingdoms. The current system recognizes six Kingdoms: Eubacteria, Archaebacteria, Plantae, Animalia, Fungi, and Protista.


The next division would be the phylum.


Several related classes make up a phylum.


Classes are further divided into Orders.


The next level of classification that orders are divided into are Families.


A genus is a group of closely related species. The genus name is the first part of the scientific name of an organism.

Species Identifier

Each species has a unique identifier that describes only that species. It is the second word in the two-word naming system of the scientific name of a species.

7 Facts About Viruses

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Influenza Virus (H1N1)
 Conceptual visualization of the Swine influenza Virus (H1N1).Science Picture Co/Subjects / Getty Images


By Regina BaileyUpdated on January 03, 2019

virus is an infectious particle that displays characteristics of life and non-life. Viruses are different from plantsanimals, and bacteria in their structure and function. They are not cells and can’t replicate on their own. Viruses must rely on a host for energy production, reproduction, and survival. Although typically only 20-400 nanometers in diameter, viruses are the cause of many human diseases including influenza, chickenpox, and the common cold.01of 07

Some Viruses Cause Cancer.

Hepatitis B viruses and DNA, illustration

Certain types of cancers have been linked to cancer viruses. Burkitt’s lymphoma, cervical cancer, liver cancer, T-cell leukemia, and Kaposi sarcoma are examples of cancers that have been associated with different types of viral infections. The majority of viral infections, however, do not cause cancer.02of 07

Some Viruses Are Naked

All viruses have a protein coating or capsid, but some viruses, such as the flu virus, have an additional membrane called an envelope. Viruses without this extra membrane are called naked viruses. The presence or absence of an envelope is an important determining factor in how a virus interacts with the host’s membrane, how it enters a host, and how it exits the host after maturation. Enveloped viruses can enter the host by fusion with the host membrane to release their genetic material into the cytoplasm, while naked viruses must enter a cell through endocytosis by the host cell. Enveloped viruses exit by budding or exocytosis by the host, but naked viruses must lyse (break open) the host cell to escape.03of 07

There Are 2 Classes of Viruses

Viruses can contain single-stranded or double-stranded DNA as the basis for their genetic material, and some even contain single-stranded or double-stranded RNA. Furthermore, some viruses have their genetic information organized as straight strands, while others have circular molecules. The type of genetic material contained in a virus not only determines which types of cells are viable hosts but also how the virus is replicated.04of 07

A Virus Can Remain Dormant in a Host for Years

Viruses undergo a life cycle with several phases. The virus first attaches to the host via specific proteins on the cell surface. These proteins are generally receptors that differ depending on the type of virus targeting the cell. Once attached, the virus then enters the cell by endocytosis or fusion. The host’s mechanisms are used to replicate the DNA or RNA of the virus as well as essential proteins. After these new viruses mature, the host is lysed to allow the new viruses to repeat the cycle.

An additional phase before replication, known as the lysogenic or dormant phase, occurs in only a select number of viruses. During this phase, the virus can remain inside the host for extended periods of time without causing any apparent changes in the host cell. Once activated, however, these viruses can immediately enter the lytic phase in which replication, maturation, and release can occur. HIV, for example, can remain dormant for 10 years.05of 07

Viruses Infect Plant, Animal, and Bacterial cells

Viruses can infect bacterial and eukaryotic cells. The most commonly known eukaryotic viruses are animal viruses, but viruses can infect plants as well. These plant viruses usually need the assistance of insects or bacteria to penetrate a plant’s cell wall. Once the plant is infected, the virus can cause several diseases which usually do not kill the plant but cause deformation in the plant’s growth and development.

A virus that infects bacteria is known as a bacteriophages or phage. Bacteriophages follow the same life cycle as eukaryotic viruses and can cause diseases in bacteria as well as destroy them through lysis. In fact, these viruses replicate so efficiently that entire colonies of bacteria can be destroyed quickly. Bacteriophages have been used in diagnosis and treatments of infections from bacteria such as E. coli and Salmonella.06of 07

Some Viruses Use Human Proteins to Infect Cells

HIV and Ebola are examples of viruses that use human proteins to infect cells. The viral capsid contains both viral proteins and proteins from the cell membranes of human cells. The human proteins help to ‘disguise’ the virus from the immune system.07of 07

Retroviruses Are Used in Cloning and Gene Therapy

A retrovirus is a type of virus that contains RNA and that replicates its genome using an enzyme known as reverse transcriptase. This enzyme converts the viral RNA to DNA that can be integrated into the host DNA. The host then uses its own enzymes to translate the viral DNA into viral RNA used for viral replication. Retroviruses have the unique ability to insert genes into human chromosomes. These special viruses have been used as important tools in scientific discovery. Scientists have patterned many techniques after retroviruses including cloning, sequencing, and some gene therapy approaches.

Biology Prefixes and Suffixes: ana-

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Anaphase I For Bluebell
Clouds Hill Imaging Ltd. / Getty Images


By Regina BaileyUpdated on March 29, 2019

Biology Prefixes and Suffixes: Ana-


The prefix (ana-) means up, upward, back, again, repetition, excessive, or apart.


Anabiosis (ana-bi-osis) – resuscitating or restoring to life from a deathlike state or condition.https://c927325d921811179fb880728854333e.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Anabolism (ana-bolism) – the process of building up or synthesizing complex biological molecules from simple molecules.

Anacathartic (ana-cathartic) – relating to the regurgitation of stomach contents; severe vomiting.

Anaclisis (ana-clisis) – an excessive emotional or physical attachment to or dependence on others.

Anacusis (ana-cusis) – the inability to perceive sound; total deafness or excessive quietness.

Anadromous (ana-dromous) – relating to fish that migrate upriver from the sea to spawn.

Anagoge (ana-goge) – a spiritual interpretation of a passage or text, seen as an upward assent or higher way of thinking.

Ananym (ana-nym) – a word that is spelled backwards, often used as a pseudonym.

Anaphase (ana-phase) – a stage in mitosis and meiosis when chromosome pairs move apart and migrate toward opposite ends of a dividing cell.

Anaphor (ana-phor) – a word that refers back to an earlier word in a sentence, used to avoid repetition.

Anaphylaxis (ana-phylaxis) – extreme sensitivity reaction to a substance, such as a drug or food product, caused by previous exposure to the substance.

Anaplasia (ana-plasia) – the process of a cell reverting to an immature form. Anaplasia is often seen in malignant tumors.

Anasarca (ana-sarca) – the excess accumulation of fluid in body tissues.

Anastomosis (ana-stom-osis) – the process by which tubular structures, such as blood vessels, connect or open into each other.

Anastrophe (ana-strophe) – an inversion of the conventional order of words.

Anatomy (ana-tomy) – the study of the form or structure of an organism that may involve dissecting or taking apart certain anatomical structures.

Anatropous (ana-tropous) – relating to a plant ovule that has become completely inverted during development so that the pore through which pollen enters is facing downward.

Biology Prefixes and Suffixes: Erythr- or Erythro-

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Erythrocytes (Red Blood Cells)
CDC / Janice Haney Carr


By Regina BaileyUpdated on February 02, 2019


The prefix erythr- or erythro- means red or reddish. It is derived from the Greek word eruthros meaning red.


Erythralgia (erythr-algia) – Disorder of the skin characterized by pain and redness of affected tissues.

Erythremia (Erythr-emia) – Abnormal increase in red blood cell numbers in the blood.

Erythrism (Erythr-ism) – Condition characterized by redness of hair, fur or plummage.

Erythroblast (Erythro-blast) – Immature nucleus-containing cell found in bone marrow that forms erythrocytes (red blood cells).

Erythroblastoma (Erythro-blastoma) – Tumor composed of cells that resemble red blood cell precursor cells known as megaloblasts.

Erythroblastopenia (Erythro-blastopenia) – Deficiency in the numbers of erythroblasts in bone marrow.

Erythrocyte (Erythro-cyte) – Cell of the blood that contains hemoglobin and transports oxygen to cells. It is also known as a red blood cell.

Erythrocytolysis (Erythro-cytolysis) – Red blood cell dissolution or destruction that allows the hemoglobin contained within the cell to escape into its surrounding environment.

Erythroderma (Erythro-derma) – Condition characterized by abnormal redness of the skin that covers a widespread area of the body.

Erythrodontia (Erythro-dontia) – Discoloration of the teeth that causes them to have a reddish appearance.

Erythroid (Erythr-oid) – Having a reddish color or pertaining to red blood cells.

Erythron (Erythr-on) – Total mass of red blood cells in the blood and the tissues from which they are derived.

Erythropathy (Erythro-pathy) – Any type of disease that involves red blood cells.

Erythropenia (Erythro-penia) – Deficiency in the numbers of erythrocytes.

Erythrophagocytosis (Erythro-phagocytosis) – Process involving the ingestion and destruction of red blood cells by a macrophage or other type of phagocyte.

Erythrophil (Erythro-phil) – Cells or tissues that are readily stained with red dyes.

Erythrophyll (Erythro-phyll) – Pigment that produces red coloration in leaves, flowers, fruit, and other forms of vegetation.

Erythropoiesis (Erythro-poiesis) – Process of red blood cell formation.

Erythropoietin (Erythro-poietin) – Hormone produced by the kidneys that stimulates bone marrow to produce red blood cells.

Erythropsin (Erythr-opsin) – Vision disorder in which objects appear to have a reddish tinge.

Biology Suffix Definition: -otomy, -tomy

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Phlebotomist taking a blood sample from patient
wathanyu / Getty Images


By Regina BaileyUpdated on July 03, 2019

The suffix “-otomy,” or “-tomy,” refers to the act of cutting or making an incision, as in a medical operation or procedure. This word part is derived from the Greek tomia, which means to cut.


Anatomy (ana-tomy): the study of the physical structure of living organisms. Anatomical dissection is a primary component of this type of biological study. Anatomy involves the study of macro-structures (heart, brain, kidneys, etc.) and microstructures (cellsorganelles, etc.).

Autotomy (aut-otomy): the act of removing an appendage from the body in order to escape when trapped. This defense mechanism is exhibited in animals such as lizards, geckos, and crabs. These animals can use regeneration to recover the lost appendage.

Craniotomy (crani-otomy): surgical cutting of the skull, typically done to provide access to the brain when surgery is needed. A craniotomy may require a small or large cut depending on the type of surgery needed. A small cut in the skull is referred to as a burr hole and is used to insert a shunt or remove small brain tissue samples. A large craniotomy is called a skull base craniotomy and is needed when removing large tumors or after an injury that causes a skull fracture.

Episiotomy (episi-otomy): surgical cut made into the area between the vagina and anus to prevent tearing during the child birthing process. This procedure is no longer routinely performed due to associated risks of infection, extra blood loss, and possible increase in the size of the cut during delivery.

Gastrotomy (gastr-otomy): surgical incision made into the stomach for the purpose of feeding an individual who is incapable of taking in food through normal processes.

Hysterotomy (hyster-otomy): surgical incision made into the uterus. This procedure is done in a Cesarean section to remove a baby from the womb. A hysterotomy is also performed in order to operate on a fetus in the womb.

Phlebotomy (phleb-otomy): incision or puncture made into a vein in order to draw blood. A phlebotomist is a health care worker who draws blood.

Laparotomy (lapar-otomy): incision made into the abdominal wall for the purpose of examining abdominal organs or diagnosing an abdominal problem. Organs examined during this procedure may include the kidneysliverspleenpancreas, appendix, stomach, intestines, and female reproductive organs.

Lobotomy (lob-otomy): incision made into a lobe of a gland or organ. Lobotomy also refers to an incision made into a lobe of the brain to sever nerve tracts.

Rhizotomy (rhiz-otomy): surgical severing of a cranial nerve root or spinal nerve root in order to relieve back pain or decrease muscle spasms.

Tenotomy (ten-otmy): incision made into the tendon in order to correct a muscle deformity. This procedure helps to lengthen a defective muscle and is commonly used to correct a club foot.

Tracheotomy (trache-otomy): incision made into the trachea (windpipe) for the purpose of inserting a tube to allow air to flow the lungs. This is done to bypass an obstruction in the trachea, such as swelling or a foreign object.

Biology Prefixes and Suffixes: hem- or hemo- or hemato-

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Blood Clot
 This is a colored scanning electron micrograph of blood clot formation during hemostasis (the first stage of wound healing in which blood clotting occurs). Credit: Science Photo Library – STEVE GSCHMEISSNER/Brand X Pictures/Getty Images


By Regina BaileyUpdated on February 03, 2019

The prefix (hem- or hemo- or hemato-) refers to blood. It is derived from the Greek (haimo-) and Latin (haemo-) for blood.

Words Beginning With: (hem- or hemo- or hemato-)

Hemangioma (hem-angioma): a tumor consisting primarily of newly formed blood vessels. It is a common benign tumor that appears as a birthmark on the skin. A hemangioma may also form on muscle, bone, or organs.

Hematic (hemat-ic): of or relating to blood or its properties.

Hematocyte (hemato-cyte): a cell of the blood or blood cell. Commonly used to refer to a red blood cell, this term can also be used to refer to white blood cells and platelets.

Hematocrit (hemato-crit): the process of separating blood cells from plasma in order to obtain the ratio of the volume of red blood cells per given volume of blood.

Hematoid (hemat-oid): – resembling or relating to blood.

Hematology (hemato-logy): field of medicine concerned with the study of blood including diseases of the blood and bone marrow. Blood cells are produced by blood-forming tissue in bone marrow.

Hematoma (hemat-oma): abnormal accumulation of blood in an organ or tissue as a result of a broken blood vessel. A hematoma can also be a cancer that occurs in the blood.

Hematopoiesis (hemato-poiesis):  the process of forming and generating blood components and blood cells of all types.

Hematuria (hemat-uria): the presence of blood in urine resulting from leakage in the kidneys or another part of the urinary tract. Hematuria may also indicate a urinary system disease, such as bladder cancer.

Hemoglobin (hemo-globin): iron-containing protein found in red blood cells. Hemoglobin binds oxygen molecules and transports oxygen to body cells and tissues through the bloodstream.

Hemolymph (hemo-lymph): fluid similar to blood that circulates in arthropods such as spiders and insects. Hemolymph may also refer to both blood and lymph of the human body.

Hemolysis (hemo-lysis): destruction of red blood cells as a result of cell rupture. Some pathogenic microbes, plant poisons, and snake venoms can cause red blood cells to rupture. Exposure to high concentrations of chemicals, such as arsenic and lead, can also cause hemolysis.

Hemophilia (hemo-philia): a sex-linked blood disorder characterized by excessive bleeding due to a defect in a blood clotting factor. A person with hemophilia has a tendency to bleed uncontrollably.

Hemoptysis (hemo-ptysis): the spewing or coughing up of blood from the lungs or airway.

Hemorrhage (hemo-rrhage): abnormal and excessive flow of blood.

Hemorrhoids (hemo-rrhoids): swollen blood vessels located in the anal canal.

Hemostasis (hemo-stasis): the first stage of wound healing in which the stoppage of blood flow from damaged blood vessels occurs.

Hemothorax (hemo-thorax): an accumulation of blood in the pleural cavity (space between the chest wall and lungs). A hemothroax may be caused by trauma to the chest, lung infections, or a blood clot in the lungs.

Hemotoxin (hemo-toxin): a toxin that destroys red blood cells by inducing hemolysis. Exotoxins produced by some bacteria are hemotoxins.

Do Hand Sanitizers Work Better Than Soap and Water?

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Hand sanitizers should not take the place of plain soap and water
 Glasshouse Images / Getty Images


By Regina BaileyUpdated on April 01, 2020

Antibacterial hand sanitizers are marketed to the public as an effective way to wash one’s hands when traditional soap and water are not available. These “waterless” products are particularly popular with parents of small children. Manufacturers of hand sanitizers claim that the sanitizers kill 99.9 percent of germs. Since you naturally use hand sanitizers to cleanse your hands, the assumption is that 99.9 percent of harmful germs are killed by the sanitizers. However, research studies suggest that this is not the case.

How Do Hand Sanitizers Work?

Hand sanitizers work by stripping away the outer layer of oil on the skin. This usually prevents bacteria present in the body from coming to the surface of the hand. However, these bacteria that are normally present in the body are generally not the kinds of bacteria that will make us sick. In a review of the research, Barbara Almanza, an associate professor at Purdue University who teaches safe sanitation practices to workers, came to an interesting conclusion. She notes that the research shows that hand sanitizers do not significantly reduce the number of bacteria on the hand and in some cases may potentially increase the number of bacteria. So the question arises, how can the manufacturers make the 99.9 percent claim?

How Can Manufacturers Make the 99.9 Percent Claim?

The manufacturers of the products test the products on bacteria-tainted inanimate surfaces, hence they are able to derive the claims of 99.9 percent of bacteria killed. If the products were fully tested on hands, there would no doubt be different results. Since there is inherent complexity in the human hand, testing hands would definitely be more difficult. Using surfaces with controlled variables is an easier way to obtain some type of consistency in the results. But, as we are all aware, everyday life is not as consistent.

Hand Sanitizer vs. Hand Soap and Water

Interestingly enough, the Food and Drug Administration, in regards to regulations concerning proper procedures for food services, recommends that hand sanitizers not be used in place of hand soap and water but only as an adjunct. Likewise, Almanza recommends that to properly sanitize the hands, soap and water should be used during hand washing. A hand sanitizer can not and should not take the place of proper cleansing procedures with soap and water.

Hand sanitizers can be a useful alternative when the option of using soap and water is not available. An alcohol-based sanitizer that contains at least 70% alcohol should be used to ensure that germs are killed. Since hand sanitizers don’t remove dirt and oils on hands, it is best to wipe your hands with a towel or napkin before applying the sanitizer.

What About Antibacterial Soaps?

Research on the use of consumer antibacterial soaps has shown that plain soaps are just as effective as antibacterial soaps in reducing bacteria-related illnesses. In fact, using consumer antibacterial soap products may increase bacterial resistance to antibiotics in some bacteria. These conclusions only apply to consumer antibacterial soaps and not to those used in hospitals or other clinical areas. Other studies suggest that ultra-clean environments and the persistent use of antibacterial soaps and hand sanitizers may inhibit proper immune system development in children. This is because inflammatory systems require greater exposure to common germs for proper development.

In September 2016, the U.S. Food and Drug Administration banned the marketing of over-the-counter antibacterial products that contain several ingredients including triclosan and triclocarban. Triclosan in antibacterial soaps and other products has been linked to the development of certain diseases.

Anatomy and Structure of Viruses

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Influenza Virus Particles
CDC / Dr. F. A. Murphy


By Regina BaileyUpdated on July 29, 2019

Scientists have long sought to uncover the structure and function of viruses. Viruses are unique in that they have been classified as both living and nonliving at various points in the history of biology. Viruses are not cells but non-living, infectious particles. They are capable of causing a number of diseases, including cancer, in various different types of organisms.

Viral pathogens not only infect humans and animals, but also plants, bacteria, protists, and archaeans. These extremely tiny particles are about 1,000 times smaller than bacteria and can be found in almost any environment. Viruses can not exist independently of other organisms as they must take over a living cell in order to reproduce.

Virus Anatomy and Structure

Virus Particle
Alfred Pasieka/Science Photo Library/Getty Images

A virus particle, also known as a virion, is essentially nucleic acid (DNA or RNA) enclosed within a protein shell or coat. Viruses are extremely small, approximately 20 – 400 nanometers in diameter. The largest virus, known as the Mimivirus, can measure up to 500 nanometers in diameter. By comparison, a human red blood cell is around 6,000 to 8,000 nanometers in diameter.

In addition to varying sizes, viruses also have a variety of shapes. Similar to bacteria, some viruses have spherical or rod shapes. Other viruses are icosahedral (polyhedron with 20 faces) or helical shaped. Viral shape is determined by the protein coat that encases and protects the viral genome.

Viral Genetic Material

Flu Virus RNA
Equinox Graphics/Science Photo Library/Getty Images

Viruses may have double-stranded DNA, double-stranded RNA, single-stranded DNA or single-stranded RNA. The type of genetic material found in a particular virus depends on the nature and function of the specific virus. The genetic material is not typically exposed but covered by a protein coat known as a capsid. The viral genome can consist of a very small number of genes or up to hundreds of genes depending on the type of virus. Note that the genome is typically organized as a long molecule that is usually straight or circular.

Viral Capsid

Polio Virus Capsid
Theasis/E+/Getty Images

The protein coat that encases viral genetic material is known as a capsid. A capsid is composed of protein subunits called capsomeres. Capsids can have several shapes: polyhedral, rod or complex. Capsids function to protect the viral genetic material from damage.

In addition to the protein coat, some viruses have specialized structures. For example, the flu virus has a membrane-like envelope around its capsid. These viruses are known as enveloped viruses. The envelope has both host cell and viral components and assists the virus in infecting its host. Capsid additions are also found in bacteriophages. For example, bacteriophages can have a protein “tail” attached to the capsid that is used to infect host bacteria.

Virus Replication

Flu Virus Replication
Steve Gschmeissner/Science Photo Library/Getty Images

Viruses are not capable of replicating their genes by themselves. They must rely on a host cell for reproduction. In order for viral replication to occur, the virus must first infect a host cell. The virus injects its genetic material into the cell and uses the cell’s organelles to replicate. Once a sufficient number of viruses have been replicated, the newly formed viruses lyse or break open the host cell and move on to infect other cells. This type of viral replication is known as the lytic cycle.

Some viruses can replicate by the lysogenic cycle. In this process, viral DNA is inserted into the DNA of the host cell. At this point, the viral genome is known as a prophage and enters a dormant state. The prophage genome is replicated along with the bacterial genome when the bacteria divide and is passed along to each bacterial daughter cell. When triggered by changing environmental conditions, the prophage DNA may become lytic and start replicating viral components within the host cell. Viruses that are non-enveloped are released from the cell by lysis or exocytosis. Enveloped viruses are commonly released by budding.

Viral Diseases

HIV Particles
BSIP/UIG/Getty Images

Viruses cause a number of diseases in the organisms they infect. Human infections and diseases caused by viruses include Ebola fever, chicken pox, measles, influenza, HIV/AIDS, and herpes. Vaccines have been effective at preventing some types of viral infections, such as small pox, in humans. They work by helping the body to build an immune system response against specific viruses.

Viral diseases that impact animals include rabies, foot-and-mouth disease, bird flu, and swine flu. Plant diseases include mosaic disease, ring spot, leaf curl, and leaf roll diseases. Viruses known as bacteriophages cause disease in bacteria and archaeans.

How Plant Viruses, Viroids, and Satellite Viruses Cause Disease

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Brome Mosaic Virus - Plant
 Brome mosaic virus (BMV) is a small, positive-stranded, icosahedral RNA plant virus of the alphavirus-like superfamily. Laguna Design/Oxford Scientific/Getty Images


By Regina BaileyUpdated on November 03, 2019

Plant viruses are viruses that infect plants. Control of plant viruses is of great economic importance worldwide, because these viruses cause diseases that destroy commercial crops. Like other viruses, a plant virus particle, also known as a virion, is an extremely small infectious agent. It is essentially a nucleic acid (DNA or RNA) enclosed in a protein coat called a capsid.

Viral genetic material can be double-stranded DNA, double-stranded RNA, single-stranded DNA, or single-stranded RNA. Most plant viruses are classified as single-stranded RNA or double-stranded RNA virus particles. Very few are single-stranded DNA, and none are double-stranded DNA particles.

Plant Viruses and Disease

Ringspots Leaves
 This photo shows orchid leaves with symptoms of ringspots resulting from a strain of tobacco mosaic virus.Department of Plant Pathology, North Carolina State University/Bugwood.org/CC BY-NC 3.0

Plant viruses cause various types of diseases, but the diseases do not typically result in plant death. They do, however, produce symptoms such as ringspots, mosaic pattern development, leaf yellowing and distortion, as well as deformed growth.

The name of the plant disease is often related to the symptoms the disease produces in a particular plant. For example, papaya leaf curl and potato leaf roll are diseases that cause specific types of leaf distortion. Some plant viruses are not limited to one particular plant host but may infect different varieties of plants. For example, plants such as tomatoes, peppers, cucumbers, and tobacco may all be infected by mosaic viruses. The brome mosaic virus commonly infects grasses, grains, and bamboos.

Plant Virus Transmission

Green Peach Aphid
 This green peach aphid (Myzus persicae) is an important transmission vector of plum pox virus.Scott Bauer/USDA Agricultural Research Service/Bugwood.org/CC BY-NC 3.0

Plant cells are eukaryotic cells that are similar to animal cells. Plant cells, however, have a cell wall that is nearly impossible for viruses to breach in order to cause infection. As a result, plant viruses are typically spread by two common mechanisms: horizontal transmission and vertical transmission.

  • Horizontal Transmission
    In this type of transmission, the plant virus is transmitted as a result of an external source. In order to “invade” the plant, the virus must penetrate the plant’s outer protective layer. Plants that have been damaged by weather, pruning, or plant vectors (bacteriafunginematodes, and insects) are typically more susceptible to a virus. Horizontal transmission also occurs by certain artificial methods of vegetative reproduction typically employed by horticulturists and farmers. Plant cutting and grafting are common modes by which plant viruses may be transmitted.
  • Vertical Transmission
    In vertical transmission, the virus is inherited from a parent. This type of transmission occurs in both asexual and sexual reproduction. In asexual reproductive methods such as vegetative propagation, the offspring develop from and are genetically identical to a single plant. When the new plants develop from the stems, roots, bulbs, etc. of the parent plant, the virus is passed along to the developing plant. In sexual reproduction, viral transmission occurs as a result of seed infection.

In most cases, scientists have been unable to find cures for plant viruses, so they have been focusing on reducing the occurrence and transmission of the viruses. Viruses are not the only plant pathogens. Infectious particles known as viroids and satellite viruses cause several plant diseases as well.

Plant Viroids

Potato Spindle Tuber Viroid
 The potato tubers on the left are infected with the potato spindle tuber viroid. The reduced size and yield of these tubers can be seen as compared to the healthy tubers on the right.European and Mediterranean Plant Protection Organization/Bugwood.org/CC BY-NC 3.0

Viroids are extremely small plant pathogens that consist of tiny single-stranded molecules of RNA, usually only a few hundred nucleotides long. Unlike viruses, they lack a protein capsid to protect their genetic material from damage. Viroids don’t code for proteins and are commonly circular in shape. Viroids are thought to interfere with a plant’s metabolism leading to underdevelopment. They disrupt plant protein production by interrupting transcription in host cells.

Transcription is a process that involves the transcribing of genetic information from DNA to RNA. The transcribed DNA message is used to produce proteins. Viroids cause a number of plant diseases that severely impact crop production. Some common plant viroids include the potato spindle tuber viroid, peach latent mosaic viroid, avocado sunblotch viroid, and the pear blister canker viroid.

Satellite Viruses

Satellite Tobacco Necrosis Virus
 This is a computer model of a satellite tobacco necrosis virus.Mehau Kulyk/Science Photo Library/Getty Images

Satellite viruses are infectious particles that are capable of infecting bacteria, plants, fungi, and animals. They code for their own protein capsid, but they rely on a helper virus in order to replicate. Satellite viruses cause plant diseases by interfering with specific plant gene activity. In some instances, plant disease development is dependent upon the presence of both the helper virus and its satellite. While satellite viruses alter the infectious symptoms caused by their helper virus, they do not influence or disrupt viral replication in the helper virus.

Plant Virus Disease Control

Tomato Spotted Wilt Virus
 These tomato fruits are showing symptoms of Tomato Spotted Wilt Virus (TSWV).William M. Brown Jr./Bugwood.org/CC BY-NC 3.0

Currently, there is no cure for plant viral disease. This means that any infected plants must be destroyed for fear of spreading disease. The best methods being employed to combat plant viral diseases are aimed at prevention. These methods include ensuring that seeds are virus-free, control of potential virus vectors through pest control products, and ensuring that planting or harvesting methods do not promote viral infection.

Plant Viruses Key Takeaways

  • Plant viruses are particles of RNA or DNA that infect plants and cause disease.
  • Most plant viruses are single-stranded RNA or double-stranded RNA viruses.
  • Common plant viruses include mosaic viruses, spotted wilt viruses, and leaf curl viruses.
  • Plant viruses are typically spread by either horizontal or verticle transmission.
  • Viroids are single-stranded molecules of RNA that cause plant diseases that lead to underdevelopment.
  • Satellite viruses are extremely small infectious particles that rely on a helper virus in order to replicate and cause plant diseases.
  • There is no cure for plant viral diseases; thus prevention remains the focus of control.

Biology Prefixes and Suffixes: Cephal-, Cephalo-

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Bigfin Reef Squid
Sha/Moment Open/Getty Images


By Regina BaileyUpdated on January 04, 2020

The word part cephal- or cephalo- means head. Variants of this affix include (-cephalic), (-cephalus), and (-cephaly).

Words Beginning With (Cephal-) or (Cephalo-)

  • Cephalad (cephal-ad): Cephalad is a directional term used in anatomy to indicate positioning toward the head or anterior end of the body.
  • Cephalalgia (cephal-algia): Pain located in or near the head is called cephalalgia. It is also known as a headache.
  • Cephalic (cephal-ic): Cephalic means of or relating to the head, or located near the head.
  • Cephalin (cephal-in): Cephalin is a type of cell membrane phospholipid found in body cells, particularly in brain and spinal cord tissue. It is also the main phospholipid in bacteria.
  • Cephalization (cephal-ization): In animal development, this term refers to the development of a highly specialized brain that processes sensory input and controls body functions.
  • Cephalocele (cephalo-cele): A cephalocele is a protrusion of part of the brain and meninges through an opening in the skull.
  • Cephalogram (cephalo-gram): A cephalogram is an X-ray of the head and facial area. It assists in obtaining accurate measurements of the jaw and facial bones and is also used as a diagnostic tool for conditions such as obstructive sleep apnea.
  • Cephalohematoma (cephalo-hematoma): A cephalohematoma is a pool of blood that collects under the scalp. It typically occurs in infants and results from pressure during the birthing process.
  • Cephalometry (cephalo-metry): The scientific measurement of the bones of the head and face is called cephalometry. Measurements are often taken using radiographic imaging.
  • Cephalopathy (cephalo-pathy): Also called encephalopathy, this term refers to any disease of the brain.
  • Cephaloplegia (cephalo-plegia): This condition is characterized by paralysis that occurs in the muscles of the head or neck.
  • Cephalopod (cephalo-pod): Cephalopods are invertebrate animals, including squid and octopuses, that appear to have limbs or feet that are attached to their heads.
  • Cephalothorax (cephalo-thorax): The fused head and thorax section of the body seen in many arthropods and crustaceans is known as the cephalothorax.

Words With (-cephal-), (-cephalic), (-cephalus), or (-cephaly)

  • Brachycephalic (brachy-cephalic): This term refers to individuals with skull bones that are shortened in length resulting in a short, broad head.
  • Encephalitis (en-cephal-itis): Encephalitis is a condition characterized by inflammation of the brain, typically caused by a viral infection. Viruses that cause encephalitis include measles, chickenpox, mumps, HIV, and herpes simplex.
  • Hydrocephalus (hydro-cephalus): Hydrocephalus is an abnormal condition of the head in which the cerebral ventricles expand, causing fluid to accumulate in the brain.
  • Leptocephalus (lepto-cephalus): This term means “slim head” and refers to having an abnormally tall and narrow skull.
  • Megacephaly (mega-cephaly): This condition is characterized by the development of an abnormally large head.
  • Megalencephaly (mega-en-cephaly): Megalencephaly is the development of an abnormally large brain. Individuals with this condition may experience seizures, paralysis, and decreased cognitive function.
  • Mesocephalic (meso-cephalic): Mesocephalic refers to having a head that is of medium size.
  • Microcephaly (micro-cephaly): This condition is characterized by an abnormally small head in relation to body size. Microcephaly is a congenital condition that can be caused by chromosome mutation, exposure to toxins, maternal infections, or trauma.
  • Plagiocephaly (plagio-cephaly): Plagiocephaly is a skull deformity in which the head appears asymmetrical with flat regions. This condition occurs in babies and results from abnormal closure of cranial sutures.
  • Procephalic (pro-cephalic): This directional anatomy term describes a position located near the front of the head.

Understanding the Definition of the “Auto” Prefix in Biology

Find Out More About Words Like Autoimmunity, Autonomic, and Autochthon

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Algae in a Lake
Moritz Haisch / EyeEm / Getty Images


By Regina BaileyUpdated on September 05, 2018

The English prefix “auto-” means self, same, occurring from within, or spontaneous. To remember this prefix, which was originally derived from the Greek word “auto” meaning “self,” easily think of common words that you know that share the “auto-” prefix like automobile (a car you drive for yourself) or automatic (description for something spontaneous or that works on its own).

Take a look at other words used for biological terms that begin with the prefix “auto-.”


Autoantibodies are antibodies that are produced by an organism that attacks the organism’s own cells and tissues. Many autoimmune diseases like lupus are caused by autoantibodies.


Autocatalysis is catalysis or the acceleration of a chemical reaction that is caused by one of the products of the reaction acting as a catalyst. In glycolysis, which is the breakdown of glucose to form energy, one part of the process is powered by autocatalysis.


Autochthon refers to the indigenous animals or plants of a region or the earliest known, native inhabitants of a country. The Aboriginal people of Australia are considered autochthons.


Autocoid means the natural internal secretion, such as a hormone, that is produced in one part of the body and affects another part of the organism. The suffix is derived from the Greek “acos” meaning relief, for example, from a drug.


Autogamy is the term for self-fertilization as in the pollination of a flower by its own pollen or the fusion of gametes resulting from the division of a single parent cell that occurs in some fungi and protozoans.


The word autogenic literally translates from Greek to mean “self-generating” or it is produced from within. For example, you can use autogenic training or self-hypnosis or mediation in an attempt to control your own body temperature or blood pressure.


In biology, autoimmunity means that an organism cannot recognize its own cells and tissues, which may trigger an immune response or attack of those parts.


Autolysis is the destruction of a cell by its own enzymes; self-digestion. The suffix lysis (also derived from Greek) means “loosening.” In English, the suffix “lysis” can mean decomposition, dissolution, destruction, loosening, breaking down, separation, or disintegration.


Autonomic refers to an internal process that occurs involuntarily or spontaneously. It is used in human biology prominently when describing the part of the nervous system which controls the body’s involuntary functions, the autonomic nervous system.


Autoploid relates to a cell that has two or more copies of a single haploid set of chromosomes. Depending on the number of copies, the autoploid can be categorized as autodiploids (two sets), autotriploids (three sets), autotetraploids (four sets), autopentaploids (five sets), or autohexaploids (six sets), and so on.


An autosome is a chromosome that is not a sex chromosome and appears in pairs in somatic cells. Sex chromosomes are known as allosomes.


An autotroph is an organism that is self-nourishing or capable of generating its own food. The suffix “-troph” which derives from Greek, means “nourishing.” Algae is an example of an autotroph.

Karyo- or Caryo- Biology Prefixes and Suffixes

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Downs syndrome karyotype, illustration


By Regina BaileyUpdated on February 08, 2019

The prefix (karyo- or caryo-) means nut or kernel and also refers to the nucleus of a cell.https://141b17efc31f19a6b108d7c5637be0d3.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html


Caryopsis (cary-opsis): fruit of grasses and grains that consists of a single-celled, seed-like fruit.https://141b17efc31f19a6b108d7c5637be0d3.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Karyocyte (karyo-cyte): a cell that contains a nucleus.

Karyochrome (karyo-chrome): a type of nerve cell in which the nucleus stains easily with dyes.

Karyogamy (karyo-gamy): uniting of cell nuclei, as in fertilization.

Karyokinesis (karyo-kinesis): division of the nucleus that occurs during the cell cycle phases of mitosis and meiosis.

Karyology (karyo-logy): the study of the structure and function of the cell nucleus.

Karyolymph (karyo-lymph): the aqueous component of the nucleus in which the chromatin and other nuclear components are suspended.

Karyolysis (karyo-lysis): the dissolution of the nucleus that occurs during cell death.

Karyomegaly (karyo-mega-ly): abnormal enlargement of the cell nucleus.

Karyomere (karyo-mere): a vesicle containing a small portion of the nucleus, typically following abnormal cell division.

Karyomitome (karyo-mitome): chromatin network within the cell nucleus.

Karyon (karyon): the cell nucleus.

Karyophage (karyo-phage): a parasite that engulfs and destroys the nucleus of a cell.

Karyoplasm (karyo-plasm): the protoplasm of the nucleus of a cell; also known as nucleoplasm.

Karyopyknosis (karyo-pyk-nosis): shrinkage of the cell nucleus that is accompanied by the condensation of chromatin during apoptosis.

Karyorrhexis (karyo-rrhexis): stage of cell death in which the nucleus ruptures and disperses its chromatin throughout the cytoplasm.

Karyosome (karyo-some): dense mass of chromatin in the nucleus of a non-dividing cell.

Karyostasis (karyo-stasis): stage of the cell cycle, also known as interphase, where the cell undergoes a period of growth in preparation for cell division. This stage occurs between two successive divisions of the cell nucleus.

Karyotheca (karyo-theca): double membrane that encloses the contents of the nucleus, also known as the nuclear envelope. Its outer portion is continuous with the endoplasmic reticulum.

Karyotype (karyo-type): an organized visual representation of the chromosomes in the cell nucleus arranged according to characteristics such as number, size, and shape.

Learn How Virus Replication Occurs

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Influenza Virus Particle
 This image shows an influenza virus particle. CDC/Frederick Murphy


By Regina BaileyUpdated on May 15, 2018

Viruses are intracellular obligate parasites, which means that they cannot replicate or express their genes without the help of a living cell. A single virus particle (virion) is in and of itself essentially inert. It lacks needed components that cells have to reproduce. When a virus infects a cell, it marshals the cell’s ribosomes, enzymes and much of the cellular machinery to replicate. Unlike what we have seen in cellular replication processes such as mitosis and meiosis, viral replication produces many progeny, that when complete, leave the host cell to infect other cells in the organism.

Viral Genetic Material

Viruses may contain double-stranded DNA, double-stranded RNA, single-stranded DNA or single-stranded RNA. The type of genetic material found in a particular virus depends on the nature and function of the specific virus. The exact nature of what happens after a host is infected varies depending on the nature of the virus. The process for double-stranded DNA, single-stranded DNA, double-stranded RNA and single-stranded RNA viral replication will differ. For example, double-stranded DNA viruses typically must enter the host cell’s nucleus before they can replicate. Single-stranded RNA viruses however, replicate mainly in the host cell’s cytoplasm.

Once a virus infects its host and the viral progeny components are produced by the host’s cellular machinery, the assembly of the viral capsid is a non-enzymatic process. It is usually spontaneous. Viruses typically can only infect a limited number of hosts (also known as host range). The “lock and key” mechanism is the most common explanation for this range. Certain proteins on the virus particle must fit certain receptor sites on the particular host’s cell surface.

How Viruses Infect Cells

The basic process of viral infection and virus replication occurs in 6 main steps.

  1. Adsorption – virus binds to the host cell.
  2. Penetration – virus injects its genome into host cell.
  3. Viral Genome Replication – viral genome replicates using the host’s cellular machinery.
  4. Assembly – viral components and enzymes are produced and begin to assemble.
  5. Maturation – viral components assemble and viruses fully develop.
  6. Release – newly produced viruses are expelled from the host cell.

Viruses may infect any type of cell including animal cellsplant cells, and bacterial cells. To view an example of the process of viral infection and virus replication, see Virus Replication: Bacteriophage. You will discover how a bacteriophage, a virus that infects bacteria, replicates after infecting a bacterial cell.01of 06

Virus Replication: Adsorption

Bacteriophage Infecting a Bacterial Cell-1
 Bacteriophage Infecting a Bacterial Cell. Copyright Dr. Gary Kaiser. Used with permission.

How Viruses Infect Cells

Step 1: Adsorption
bacteriophage binds to the cell wall of a bacterial cell.https://6fb1307be2b8bdc28822e11f50ca3b9b.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html02of 06

Virus Replication: Penetration

Bacteriophage Infecting a Bacterial Cell - 2
 Bacteriophage Infecting a Bacterial Cell. Copyright Dr. Gary Kaiser. Used with permission.

How Viruses Infect Cells

Step 2: Penetration
The bacteriophage injects its genetic material into the bacterium.https://6fb1307be2b8bdc28822e11f50ca3b9b.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html03of 06

Virus Replication: Replication

Bacteriophage Infecting a Bacterial Cell - 3
 Bacteriophage Infecting a Bacterial Cell. Copyright Dr. Gary Kaiser. Used with permission.

How Viruses Infect Cells

Step 3: Viral Genome Replication
The bacteriophage genome replicates using the bacterium‘s cellular components.https://6fb1307be2b8bdc28822e11f50ca3b9b.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html04of 06

Virus Replication: Assembly

Bacteriophage Infecting a Bacterial Cell - 4
 Bacteriophage Infecting a Bacterial Cell. Copyright Dr. Gary Kaiser. Used with permission.

How Viruses Infect Cells

Step 4: Assembly
Bacteriophage components and enzymes are produced and begin to assemble.https://6fb1307be2b8bdc28822e11f50ca3b9b.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html05of 06

Virus Replication: Maturation

Bacteriophage Infecting a Bacterial Cell - 5
 Bacteriophage Infecting a Bacterial Cell. Copyright Dr. Gary Kaiser. Used with permission.

How Viruses Infect Cells

Step 5: Maturation
Bacteriophage components assemble and phages fully develop.https://6fb1307be2b8bdc28822e11f50ca3b9b.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html06of 06

Virus Replication: Release

Bacteriophage Infecting a Bacterial Cell - 6
 Bacteriophage Infecting a Bacterial Cell. Copyright Dr. Gary Kaiser. Used with permission.

How Viruses Infect Cells

Step 6: Release
bacteriophage enzyme breaks down the bacterial cell wall causing the bacterium to split open.

Biology Prefixes and Suffixes: Ect- or Ecto-

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Spitting Cobra
 Spitting Cobra: Snakes and other reptiles are ectotherms and must obtain heat from their external environment.Digital Vision / Getty Images


By Regina BaileyUpdated on September 07, 2019

The prefix ecto- comes from the Greek ektos, which means outside. (Ecto-) means outer, external, out, or outside. Related prefixes include (ex- or exo-).https://b3bb79d2474ab13efb3843e63a187b75.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Words Beginning With (Ecto-)

Ectoantigen (ecto – antigen): An antigen that is located on the surface or exterior of a microbe is known as an ectoantigen. An antigen is any substance that elicits an antibody immune response.https://b3bb79d2474ab13efb3843e63a187b75.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Ectoblast (ecto – blast): a synonym for an epiblast or an ectoderm.

Ectocardia (ecto – cardia): This congenital condition is characterized by displacement of the heart, particularly a heart that is outside of the chest cavity.

Ectocellular (ecto – cellular): of or pertaining to an object external to a cell or outside of the cell membrane.

Ectocornea (ecto – cornea): The ectocornea is the outer layer of the cornea. The cornea is the clear, protective layer of the eye.

Ectocranial (ecto – cranial): This term describes a position that is external to the skull.

Ectocytic (ecto – cytic): This term means outside of or external to a cell.

Ectoderm (ecto – derm): Ectoderm is the outer germ layer of a developing embryo that forms skin and nervous tissue.

Ectodomain (ecto – domain): a biochemical term that denotes the part of a polypeptide on the cell membrane that reaches into the extracellular space.

Ectoenzyme (ecto – enzyme): An ectoenzyme is an enzyme that is attached to the outer cell membrane and is secreted externally.https://b3bb79d2474ab13efb3843e63a187b75.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Ectogenesis (ecto – genesis): The development of an embryo outside of the body, in an artificial environment, is the process of ectogenesis.

Ectohormone (ecto – hormone): An ectohormone is a hormone, such as a pheromone, that is excreted from the body into the external environment. These hormones typically alter the behavior of other individuals of the same or different species.

Ectomere (ecto – mere): This term refers to any blastomere (a cell resulting from cell division that occurs after fertilization) that forms the embryonic ectoderm.

Ectomorph (ecto – morph): An individual with a tall, lean, thin body type predominated by tissue derived from the ectoderm is called an ectomorph.

Ectoparasite (ecto – parasite): An ectoparasite is a parasite that lives on the outer surface of its host. Examples include fleas, lice, and mites.

Ectophyte (ecto – phyte): An ectophyte is a parasitic plant that lives on the outer surface of its host.

Ectopia (ecto – pia): The abnormal displacement of an organ or body part outside of its proper location is known as ectopia. An example is ectopia cordis, a congenital condition where the heart sits outside of the chest cavity.

Ectopic (ecto – pic): Anything that occurs out of place or in an abnormal position is called ectopic. In an ectopic pregnancy, a fertilized egg attaches to a fallopian tube wall or other surface that is outside of the uterus. Similarly, an ectopic beat refers to electrical disturbances in the heart outside of the normal initiation in the SA node.

Ectoplasm (ecto – plasm): The outer area of the cytoplasm in some cells, such as protozoans, is known as ectoplasm.

Ectoproct (ecto – proct): synonym for a bryozoan.

Ectoprocta (ecto – procta): animals commonly known as oryonzoans. Ectoprocta is a phylum of non-motile aquatic animals. While the individuals are very small, the colonies that they live in can grow comparatively quite large.

Ectoprotein (ecto – protein): Also called an exoprotein, an ectoprotein is the term for an extracellular protein.

Ectorhinal (ecto – rhinal): This term refers to the exterior of the nose.

Ectosarc (ecto – sarc): The ectoplasm of a protozoan, such as an amoeba, is called the ectosarc.

Ectosome (ecto – some): An ectosome, also called an exosome, is an extracelluar vesicle that is often involved in cell-to-cell communication. These vesicles that contain proteins, RNA, and other signaling molecules bud off from the cell membrane.

Ectotherm (ecto – therm): An ectotherm is an organism (like a reptile) that uses external heat to regulate its body temperature.

Ectotrophic (ecto – trophic): This term describes organisms that grow and obtain nutrients from the surface of tree roots, such as mycorrhiza fungi.

Ectozoa (ecto – zoa): refers to animal parasites who live externally on other animals. Examples include the louse or the flea, both parasitic insects.

Ectozoon (ecto – zoon): An ectozoon is an ectoparasite living on the surface of its host.

Biology Prefixes and Suffixes: glyco-, gluco-

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Heap of Sugar Cubes
 Heap of Sugar Cubes. Maximilian Stock Ltd./Photographer’s Choice/Getty Images


By Regina BaileyUpdated on September 09, 2019

The prefix (glyco-) means a sugar or refers to a substance that contains a sugar. It is derived from the Greek glukus for sweet. (Gluco-) is a variant of (glyco-) and refers to the sugar glucose.

Words Beginning With: (Gluco-)

Glucoamylase (gluco – amyl – ase): Glucoamylase is a digestive enzyme that breaks down carbohydrates, such as starch, by removing glucose molecules.

Glucocorticoid (gluco – corticoid): Named for their role in glucose metabolism, glucocorticoids are steroid hormones made in the cortex of the adrenal glands. These hormones reduce inflammation and suppress immune system activity. Cortisol is an example of a glucocorticoid.https://d62828972b0ef6ea2518fe1baa6ef11d.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Glucokinase (gluco – kinase): Glukinase is an enzyme found in liver and pancreas cells that helps to regulate glucose metabolism. It uses energy in the form of ATP for the phosphorylation of glucose.

Glucometer (gluco – meter): This medical device is used to measure blood glucose concentration levels. Individuals with diabetes often use a glucometer to monitor their glucose levels.

Gluconeogenesis (gluco – neo – genesis): The process of producing the sugar glucose from sources other than carbohydrates, such as amino acids and glycerol, is called gluconeogenesis.

Glucophore (gluco – phore): Glucophore refers to the group of atoms in a molecule that give the substance a sweet taste.

Glucosamine (glucos – amine): This amino sugar is a component of many polysaccharides including those that compose chitin (component of animal exoskeletons) and cartilage. Glucosamine is taken as a dietary supplement and is used to treat arthritis symptoms.

Glucose (glucose): This carbohydrate sugar is the major source of energy for the body. It is produced by photosynthesis and found in plant and animal tissues.

Glucosidase (gluco – sid – ase): This enzyme is involved in the break down of glucose storing complex carbohydrates such as glycogen and starch.

Glucotoxicity (gluco – toxic – ity): This condition develops as a result of the toxic effects of consistently high glucose levels in the blood. Glucotoxicity is characterized by decreased insulin production and increased insulin resistance in body cells.

Words Beginning With: (Glyco-)

Glycocalyx (glyco – calyx): This protective outer covering in some prokaryotic and eukaryotic cells is composed of glycoproteins and glycolipids. The glycocalyx may be highly organized forming a capsule around the cell, or it may be less structured forming a slime layer.https://d62828972b0ef6ea2518fe1baa6ef11d.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Glycogen (glyco – gen): The carbohydrate glycogen is composed of glucose and stored in the liver and muscles of the body. It is converted to glucose when blood glucose levels are low.

Glycogenesis (glyco – genesis): Glycogenesis is the process by which glucose is converted to glycogen in the body when blood glucose levels are high.

Glycogenolysis (glyco – geno – lysis): This metabolic process is the opposite of glycogenesis. In glycogenolysis, glycogen is broken down into glucose when blood glucose levels are low.

Glycol (glycol): Glycol is a sweet, colorless liquid that is used as antifreeze or as a solvent. This organic compound is an alcohol that is poisonous if ingested.

Glycolipid (glyco – lipid): Glycolipids are a class of lipids with one or more carbohydrate sugar groups. Glycolipids are components of the cell membrane.

Glycolysis (glyco – lysis): Glycolysis is a metabolic pathway that involves the splitting of sugars (glucose) for the production of pyruvic acid and the release of energy in the form of ATP. It is the first step of both cellular respiration and fermentation.

Glycometabolism (glyco – metabolism): The metabolism of sugar and other carbohydrates in the body is known as glycometabolism.

Glyconanoparticle (glyco – nano – particle): a nanoparticle that is made up of carbohydrates (usually glycans).

Glycopattern (glyco – pattern): a cytological term that refers to the specific pattern of glycosides found in a biological test sample.

Glycopenia (glyco – penia): Also known as glucopenia or hypoglycemia, glycopenia is a condition characterized by glucose deficiency in the blood. Symptoms of this condition include sweating, anxiety, nausea, dizziness, and difficulty speaking and concentrating.

Glycopexis (glyco – pexis): Glycopexis is the process of storing sugar or glycogen in body tissues.

Glycoprotein (glyco – protein): A glycoprotein is a complex protein that is linked to one or more carbohydrate chains. Glycoproteins are assembled in the cell’s endoplasmic reticulum and Golgi complex.

Glycorrhea (glyco – rrhea): Glycorrhea is a discharge of sugar from the body, typically excreted in urine.

Glycosamine (glycos – amine): Also known as glucosamine, this amino sugar is used in the building of connective tissue, exoskeletons, and cell walls.

Glycosemia (glyco – semia): This term refers to the presence of glucose in the blood. It is alternatively known as glycemia.

Glycosome (glyco – some): This organelle is found in some protazoa and contains enzymes involved in glycolysis. The term glycosome also refers to non-organelle, glycogen-storing structures in the liver.

Glycosuria (glycos – uria): Glycosuria is the abnormal presence of sugar, particularly glucose, in the urine. This is often an indicator of diabetes.

Glycosyl (glyco – syl): Glycosyl refers to a biochemical term for a chemical group that comes from cyclic glycose when a certain type of hydroxyl group is removed.

Glycosylation (glyco – sylation): The addition of a saccharide or saccharides to either a lipid or a protein to form a new molecule (glycolipid or glycoprotein).

Biology Prefixes and Suffixes: My- or Myo-

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Skeletal Muscle Fiber
 This is a colored scanning electron micrograph (SEM) of a skeletal, or striated, muscle fiber. Steve Gschmeissner/Science Photo Library/Getty Images


By Regina BaileyUpdated on May 11, 2019

The prefix myo- or my- means muscle. It is used in a number of medical terms in reference to muscles or muscle-related disease.https://e7b0e36f4d1df5a0d1d43b81366edfea.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Words Beginning With (Myo- or My-)

Myalgia (my-algia): The term myalgia means muscle pain. Myalgia may occur due to muscle injury, overuse, or inflammation.

Myasthenia (my-asthenia): Myasthenia is a disorder that causes muscle weakness, typically of voluntary muscles in the face.https://e7b0e36f4d1df5a0d1d43b81366edfea.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Myoblast (myo-blast): The embryonic cell layer of the mesoderm germ layer that develops into muscle tissue is called myoblast.

Myocarditis (myo-card-itis): This condition is characterized by inflammation of the muscular middle layer (myocardium) of the wall of the heart.

Myocardium (myo-cardium): The muscular middle layer of the wall of the heart.

Myocele (myo-cele): A myocele is a protrusion of a muscle through its sheath. It is also called a muscle hernia.

Myoclonus (myo-clonus): A brief involuntary contraction of a muscle or muscle group is known as myoclonus. These muscle spasms occur suddenly and randomly. A hiccup is an example of a myoclonus.

Myocyte (myo-cyte): A myocyte is a cell that is found in muscle tissue.

Myodystonia (myo-dystonia): Myodystonia is a muscle tone disorder.

Myoelectric (myo-electric): This terms refers to the electrical impulses that generate muscle contractions.

Myofibril (myo-fibril): A myofibril is a long, thin muscle fiber thread.https://e7b0e36f4d1df5a0d1d43b81366edfea.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Myofilament (myo-fil-ament): A myofilament is a myofibril filament composed of actin or myosin proteins. It plays an important role in the regulation of muscle contractions.

Myogenic (myo-genic): This term means originating in or arising from the muscles.

Myogenesis (myo-genesis): Myogenesis is the formation of muscle tissue occurring in embryonic development.

Myoglobin (myo-globin): Myoglobin is the oxygen-storing protein found in muscle cells. It is only found in the bloodstream following a muscle injury.

Myogram (myo-gram): A myogram is a graphical recording of muscle activity.

Myograph (myo-graph): The instrument for recording muscle activity is known as a myograph.

Myoid (my-oid): This term means resembling muscle or muscle-like.

Myolipoma (myo-lip-oma): This is a type of cancer that consists partly of muscle cells and mostly of adipose tissue.

Myology (myo-logy): Myology is the study of muscles.

Myolysis (myo-lysis): This term refers to the breakdown of muscle tissue.

Myoma (my-oma): A benign cancer consisting primarily of muscle tissue is called a myoma.

Myomere (myo-mere): A myomere is a section of skeletal muscle that is separated from other myomeres by layers of connective tissue.

Myometrium (myo-metrium): Myometrium is the middle muscular layer of the uterine wall.

Myonecrosis (myo-necrosis): The death or destruction of muscle tissue is known as myonecrosis.

Myorrhaphy (myo-rrhaphy): This term refers to the suture of muscle tissue.

Myosin (myo-sin): Myosin is the primary contractile protein in muscle cells that enables muscle movement.

Myositis (myos-itis): Myositis is muscle inflammation that causes swelling and pain.

Myotome (myo-tome): A group of muscles connected by the same nerve root is called a myotome.

Myotonia (myo-tonia): Myotonia is a condition in which the ability to relax a muscle is impaired. This neuromuscular condition may impact any muscle group.

Myotomy (my-otomy): A myotomy is a surgical procedure that involves the cutting of a muscle.

Myotoxin (myo-toxin): This is a type of toxin produced by venomous snakes that causes muscle cell death.

Biology Prefixes and Suffixes: -Phile, -Philic

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Water Bear
 This tiny aquatic invertebrate is called a Tardigrade or water bear. It is a highly resistant extremophilic animal, capable of inhabiting a vast range of altitudes, depths, salinities and temperature ranges, commonly found on mosses or lichens. Photolibrary/Oxford Scientific/Getty Image


By Regina BaileyUpdated on May 20, 2018

The suffix -phile comes from the Greek philos, which means to love. Words that end with (-phile) refer to someone or something that loves or has a fondness of, attraction to, or affection for something. It also means to have a tendency toward something. Related terms include (-philic),(-philia), and (-philo).https://b3ad4be93864791274f9833f63cee204.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Words Ending With (-Phile)

Acidophile (acido-phile): Organisms that thrive in acidic environments are called acidophiles. They include some bacteria, archaeans, and fungi.https://b3ad4be93864791274f9833f63cee204.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Alkaliphile (alkali-phile): Alkaliphiles are organisms that thrive in alkaline environments with a pH above 9. They live in habitats such as carbonate-rich soils and alkaline lakes.

Barophile (baro-phile): Barophiles are organisms that live in high-pressure habitats, such as deep-sea environments.

Electrophile (electro-phile): An electrophile is a compound that is attracted to and accepts electrons in a chemical reaction.

Extremophile (extremo-phile): An organism that lives and thrives in extreme environments is known as an extremophile. Such habitats include volcanic, salty, or deep-sea environments.

Halophile (halo-phile): A haloophile is an organism that thrives in environments with high salt concentrations, such as salt lakes.

Pedophile (pedo-phile): A pedophile is an individual who has an abnormal attraction to or affection for children.

Psychrophile (psychro-phile): An organism that thrives in very cold or frozen environments is a psychrophile. They live in polar regions and deep sea habitats.

Xenophile (xeno-phile): A xenophile is one who is attracted to all things foreign including people, languages, and cultures.

Zoophile (zoo-phile): An individual who loves animals is a zoophile. This term can also refer to people who have an abnormal sexual attraction to animals.

Words Ending With (-Philia)

Acrophilia (acro-philia): Acrophilia is a love of heights or elevated regions.

Algophilia (algo-philia): Algophilia is a love of pain.

Autophilia (auto-philia): Autophilia is a narcissistic type of self-love.

Basophilia (baso-philia): Basophilia describes cells or cell components that are attracted to basic dyes. White blood cells called basophils are examples of this type of cell. Basophilia also describes a blood condition in which there is an increase in basophils in circulation.

Hemophilia (hemo-philia): Hemophilia is a sex-linked blood disorder characterized by excessive bleeding due to a defect in a blood clotting factor. A person with hemophilia has a tendency toward bleeding uncontrollably.

Necrophilia (necro-philia): This term refers to having an abnormal fondness of or attraction to dead bodies.

Spasmophilia (spasmo-philia): This nervous system condition involves motor neurons that are overly sensitive and induce convulsions or spasms.

Words Ending With (-Philic)

Aerophilic (aero-philic): Aerophilic organisms depend on oxygen or air for survival.

Eosinophilic (eosino-philic): Cells or tissues that are readily stained with eosin dye are called eosinophilic. White blood cells called eosinophils are examples of eosinophilic cells.

Hemophilic (hemo-philic): This term refers to organisms, particularly bacteria, that have an affinity for red blood cells and grow well in blood cultures. It also refers to individuals with hemophilia.

Hydrophilic (hydro-philic): This term describes a substance that has a strong attraction to or affinity for water.

Oleophilic (oleo-philic): Substances that have a strong affinity for oil are called oleophilic.

Oxyphilic (oxy-philic): This term describes cells or tissues that have an affinity for acid dyes.

Photophilic (photo-philic): Organisms that are attracted to and thrive in light are known as photophilic organisms.

Thermophilic (thermo-philic): Thermophilic organisms are those that live and thrive in hot environments.

Biology Prefixes and Suffixes: -stasis

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Cancer Cell Metastasis
 Cancer Cell Metastasis. Susan Arnold/National Cancer Institute/Science Photo Library/Getty Images


By Regina BaileyUpdated on May 05, 2019

The suffix (-stasis) refers to having a state of balance, stability or equilibrium. It also refers to a slowing or stoppage of motion or activity. Stasis can also mean to place or position.https://4ecd965c602539923be994de33d34928.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html


Angiostasis (angio-stasis) – the regulation of new blood vessel generation. It is the opposite of angiogenesis.https://4ecd965c602539923be994de33d34928.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Apostasis (apo-stasis) – the end stages of a disease.

Astasis (a-stasis) – also called astasia, it is the inability to stand due to impairment of motor function and muscle coordination.

Bacteriostasis (bacterio-stasis) – the slowing down of bacterial growth.

Cholestasis (chole-stasis) – an abnormal condition in which the flow of bile from the liver to the small intestines is obstructed.

Coprostasis (copro-stasis) – constipation; difficulty in passing waste material.

Cryostasis (cryo-stasis) – the process involving the deep-freezing of biological organisms or tissues for preservation after death.

Cytostasis (cyto-stasis) – the inhibition or stoppage of cell growth and replication.

Diastasis (dia-stasis) – the middle portion of the diastole phase of the cardiac cycle, where blood flow entering the ventricles is slowed or stops prior to the beginning of the systole phase.

Electrohemostasis (electro-hemo-stasis) – the stoppage of blood flow through the use of a surgical instrument that uses heat generated by an electrical current to cauterize tissue.

Enterostasis (entero-stasis) – the stoppage or slowing down of matter in the intestines.

Epistasis (epi-stasis) – a type of gene interaction in which the expression of one gene is influenced by the expression of one or more different genes.

Fungistasis (fungi-stasis) – the inhibition or slowing down of fungal growth.

Galactostasis (galacto-stasis) – the stoppage of milk secretion or lactation.

Hemostasis (hemo-stasis) – the first stage of wound healing in which the stoppage of blood flow from damaged blood vessels occurs.

Homeostasis (homeo-stasis) – the ability to maintain a constant and stable internal environment in response to environmental changes. It is a unifying principle of biology.

Hypostasis (hypo-stasis) – the excess accumulation of blood or fluid in the body or an organ as a result of poor circulation.

Lymphostasis (lympho-stasis) – slowing down or obstruction of the normal flow of lymph. Lymph is the clear fluid of the lymphatic system.

Leukostasis (leuko-stasis) – the slowing down and clotting of blood due to the excess accumulation of white blood cells (leukocytes). This condition is often seen in patients with leukemia.

Menostasis (meno-stasis) – the stoppage of menstruation.

Metastasis (meta-stasis) – the placement or spreading of cancer cells from one location to another, typically through the bloodstream or lymphatic system.

Mycostasis (myco-stasis) – the prevention or inhibition of the growth of fungi.

Myelodiastasis (myelo-dia-stasis) – a condition characterized by the deterioration of the spinal cord.

Proctostasis (procto-stasis) – constipation due to stasis that occurs in the rectum.

Thermostasis (thermo-stasis) – the ability to maintain a constant internal body temperature; thermoregulation.

Thrombostasis (thrombo-stasis) – stoppage of blood flow due to the development of a stationary blood clot. Clots are formed by platelets, also known as thrombocytes.

Biology Prefixes and Suffixes: Derm- or -Dermis

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Skin Cells
 This image shows squamous cells from the surface of the skin. These are flat, keratinized, dead cells that are continuously sloughed off and replaced with new cells from below. Science Photo Library/Getty Images


By Regina BaileyUpdated on September 08, 2019

The affix derm comes from the Greek derma, which means skin or hide. Dermis is a variant form of derm, and both mean skin or covering.https://9faecfbceea4f229998b9c9efe9a9e75.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Words Beginning With (Derm-)

Derma (derm – a): The word part derma is a variant of dermis, meaning skin. It is commonly used to indicate a skin disorder such as in scleroderma (extreme hardness of skin) and xenoderma (extremely dry skin).https://9faecfbceea4f229998b9c9efe9a9e75.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Dermabrasion (derm – abrasion): Dermabrasion is a type of surgical skin treatment performed to remove the outer layers of skin. It is used to treat scars and wrinkles.

Dermatitis (dermat – itis): This is a general term for inflammation of the skin that is characteristic of a number of skin conditions. Dermatitis is a form of eczema.

Dermatogen (dermat – ogen): The term dermatogen may refer to the antigen of a particular skin disease or to a layer of plant cells thought to give rise to the plant epidermis.

Dermatologist (dermat – ologist): a doctor who specializes in dermatology and one who treats disorders of the skin, hair and nails.

Dermatology (dermat – ology): Dermatology is the area of medicine devoted to the study of the skin and skin disorders.

Dermatome (dermat – ome): Dermatome is a portion of skin containing nerve fibers from a single, posterior spinal root. Human skin has many skin zones or dermatomes. This term is also the name of a surgical instrument used for obtaining thin sections of skin for grafting.https://9faecfbceea4f229998b9c9efe9a9e75.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Dermatophyte (dermato – phyte): A parasitic fungus that causes skin infections, such as ringworm, is called a dermatophyte. They metabolize keratin in skin, hair, and nails.

Dermatoid (derma – toid): This term refers to something that is skin-like or resembles skin.

Dermatosis (dermat – osis): Dermatosis is the general term for any type of disease that affects the skin, excluding those that cause inflammation.

Dermestid (derm – estid): refers to beetles belonging to the family Dermestidae. The larvae of the family typically feed on animal fur or hides.

Dermis (derm – is): The dermis is the vascular inner layer of the skin. It lies between the epidermis and hypodermis skin layers.

Words Ending With (-Derm)

Ectoderm (ecto – derm): Ectoderm is the outer germ layer of a developing embryo that forms skin and nervous tissue.

Endoderm (endo – derm): The inner germ layer of a developing embryo that forms the lining of the digestive and respiratory tracts is the endoderm.

Exoderm (exo – derm): Another name for ectoderm is exoderm.

Mesoderm (meso – derm): The mesoderm is the middle germ layer of a developing embryo that forms connective tissues such as musclebone, and blood.

Ostracoderm (ostraco – derm): refers to a group of extinct jawless fish whose bodies had bony protective scales or plates.

Pachyderm (pachy – derm): A pachyderm is a large mammal with very thick skin, such as an elephant, hippopotamus, or rhinoceros.

Periderm (peri – derm): The outer protective plant tissue layer that surrounds roots and stems is called the periderm.

Phelloderm (phello – derm): Phelloderm is the thin layer of plant tissue, consisting of parenchyma cells, that forms a secondary cortex in woody plants.

Placoderm (placo – derm): This is the name of a prehistoric fish with plated skin around the head and thorax. The plated skin gave the appearance of armor.

Protoderm (proto – derm): refers to a plant’s primary meristem from which the epidermis is derived.

Words Ending With (-Dermis)

Endodermis (endo – dermis): The endodermis is the innermost layer in a plant’s cortex. It helps to regulate the flow of minerals and water in the plant.

Epidermis (epi – dermis): The epidermis is the outermost layer of the skin, composed of epithelial tissue. This layer of skin provides a protective barrier and serves as the first line of defense against potential pathogens.

Exodermis (exo – dermis): synonym for a plant’s hypodermis.

Hypodermis (hypo – dermis): The hypodermis is the innermost layer of the skin, composed of fat and adipose tissue. It insulates the body and cushions and protects internal organs. It is also the outermost layer in a plant’s cortex.

Rhizodermis (rhizo – dermis): The outer layer of cells in plant roots is called the rhizodermis.

Subdermis (sub – dermis): an anatomical term that refers to subcutaneous tissue in an organism.

Biology Prefixes and Suffixes: Zoo- or Zo-

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Cheetah Licking
 Zoology is the study of animals. Senchy/Moment Open/Getty Image


By Regina BaileyUpdated on May 20, 2018

The prefix zoo- or zo- refers to animals and animal life. It is derived from the Greek zōion, meaning animal.https://79a359d509a4735067b017e4d68b2f99.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Words Beginning With (Zoo- or Zo-)

Zoobiotic (zoo-bio-tic): The term zoobiotic refers to an organism that is a parasite living on or in an animal.

Zooblast (zoo-blast): A zooblast is an animal cell.

Zoochemistry (zoo-chemistry): Zoochemistry is the branch of science that focuses on animal biochemistry.https://79a359d509a4735067b017e4d68b2f99.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Zoochory (zoo-chory): The spreading of plant products such as fruit, pollen, seeds, or spores by animals is called zoochory.

Zooculture (zoo-culture): Zooculture is the practice of raising and domesticating animals.

Zoodermic (zoo-derm-ic): Zoodermic refers to the skin of an animal, particularly as it pertains to a skin graft.

Zooflagellate (zoo-flagellate): This animal-like protozoan has a flagellum, feeds on organic matter, and is often a parasite of animals.

Zoogamete (zoo-gam-ete): A zoogamete is a gamete or sex cell that is motile, such as a sperm cell.

Zoogenesis (zoo-gen-esis): The origin and development of animals is known as zoogenesis.

Zoogeography (zoo-geography): Zoogeography is the study of the geographical distribution of animals around the world.

Zoograft (zoo-graft): A zoograft is the transplantation of animal tissue to a human.https://79a359d509a4735067b017e4d68b2f99.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Zookeeper (zoo-keeper): A zookeeper is an individual who takes care of animals in a zoo.

Zoolatry (zoo-latry): Zoolatry is an excessive devotion to animals, or the worship of animals.

Zoolith (zoo-lith): A petrified or fossilized animal is called a zoolith.

Zoology (zoo-logy): Zoology is the field of biology that focuses on the study of animals or the animal kingdom.

Zoometry (zoo-metry): Zoometry is the scientific study of the measurements and sizes of animals and animal parts.

Zoomorphism (zoo-morph-ism): Zoomorphism is the use of animal forms or symbols in art and literature to assign animal characteristics to humans or dieties.

Zoon (zoo-n): An animal that develops from a fertilized egg is called a zoon.

Zoonosis (zoon-osis): Zoonosis is a type of disease that can be spread from an animal to a human. Examples of zoonotic diseases include rabies, malaria, and Lyme disease.

Zooparasite (zoo-parasite): A parasite of an animal is a zooparasite. Common zooparasites include worms and protozoa.

Zoopathy (zoo-path-y): Zoopathy is the science of animal diseases.

Zoopery (zoo-pery): The act of performing experiments on animals is termed zoopery.

Zoophagy (zoo-phagy): Zoophagy is the feeding on or eating of an animal by another animal.

Zoophile (zoo-phile): This term refers to an individual who loves animals.

Zoophobia (zoo-phobia): The irrational fear of animals is called zoophobia.

Zoophyte (zoo-phyte): A zoophyte is an animal, such as a sea anemone, that resembles a plant.

Zooplankton (zoo-plankton): Zooplankton is a type of plankton composed of tiny animals, animal-like organisms, or microscopic protists such as dinoflagellates.

Zooplasty (zoo-plasty): The surgical transplantation of animal tissue to a human is called zooplasty.

Zoosphere (zoo-sphere): The zoosphere is the global community of animals.

Zoospore (zoo-spore):  Zoospores are asexual spores produced by some algae and fungi that are motile and move by cilia or flagella.

Zootaxy (zoo-taxy): Zootaxy is the science of animal classification.

Zootomy (zoo-tomy): The study of animal anatomy, typically through dissection, is known as zootomy.

Biology Prefixes and Suffixes: -Osis, -Otic

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 Atherosclerosis is a hardening of the arteries. This image shows an artery with cutaway section to reveal deposits of plague narrowing the passage for blood flow, illustrating the condition atherosclerosis. Credit: Science Picture Co/Collection Mix: Subjects/Getty Images


By Regina BaileyUpdated on May 20, 2018

Suffixes: -Osis and -Otic

The suffix -osis means to be affected with something or can refer to an increase. It also means a condition, state, abnormal process, or disease.https://d72c707d937bfbec8156f7cd4de43f34.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

The suffix -otic means of or relating to a condition, state, abnormal process, or disease. It can also mean an increase of a certain kind.

Words Ending With (-Osis)

Apoptosis (a-popt-osis): Apoptosis is the process of programmed cell death. The purpose of this process is to remove diseased or damaged cells from the body without causing harm to other cells. In apoptosis, the damaged or diseased cell initiates self-destruction.https://d72c707d937bfbec8156f7cd4de43f34.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Atherosclerosis (athero-scler-osis): Atherosclerosis is a disease of the arteries characterized by the build up of fatty substances and cholesterol on the artery walls.

Cirrhosis (cirrh-osis): Cirrhosis is a chronic disease of the liver commonly caused by viral infection or alcohol abuse.

Exocytosis (exo-cyt-osis): This is the process by which cells move cellular molecules, such as proteins, out of the cell. Exocytosis is a type of active transport in which molecules are enclosed within transport vesicles that fuse with the cell membrane and expel their contents to the exterior of the cell.

Halitosis (halit-osis): This condition is characterized by chronic bad breath. It may be caused by gum disease, tooth decay, an oral infection, dry mouth, or other diseases (gastric reflux, diabetes, etc.).

Leukocytosis (leuko-cyt-osis): The condition of having an increased white blood cell count is called leukocytosis. A leukocyte is a white blood cell. Leukocytosis is commonly caused by an infection, allergic reaction, or inflammation.https://d72c707d937bfbec8156f7cd4de43f34.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Meiosis (mei-osis): Meiosis is a two-part cell division process for the production of gametes.

Metamorphosis (meta-morph-osis): Metamorphosis is a transformation in the physical condition of an organism from an immature state to an adult state.

Osmosis (osm-osis): The spontaneous process of water diffusion across a membrane is osmosis. It is a type of passive transport in which water moves from an area of high solute concentration to an area of low solute concentration.

Phagocytosis (phagocyt-osis): This process involves the engulfing of a cell or particle. Macrophages are examples of cells that engulf and destroy foreign substances and cell debris in the body.

Pinocytosis (pino-cyt-osis): Also called cell drinking, pinocytosis is the process by which cells ingest fluids and nutrients.

Symbiosis (sym-bi-osis): Symbiosis is the state of two or more organisms living together in community. The relationships between the organisms vary and may include mutualistic, commensalistic, or parasitic interactions.

Thrombosis (thromb-osis): Thrombosis is a condition that involves the formation of blood clots in blood vessels. The clots are formed from platelets and obstruct blood flow.

Toxoplasmosis (toxoplasm-osis): This disease is caused by the parasite Toxoplasma gondii. Although commonly seen in domesticated cats, the parasite can be transmitted to humans. It can infect the human brain and influence behavior.

Tuberculosis (tubercul-osis): Tuberculosis is an infectious disease of the lungs caused by Mycobacterium tuberculosis bacteria.

Words Ending With (-Otic)

Abiotic (a-biotic): Abiotic refers to factors, conditions, or substances that are not derived from living organisms.

Antibiotic (anti-bi-otic): The term antibiotic refers to a class of chemicals that are capable of killing bacteria and other microbes.

Aphotic (aph-otic): Aphotic relates to a certain zone in a body of water where photosynthesis does not occur. The lack of light in this zone makes photosynthesis impossible.

Cyanotic (cyan-otic): Cyanotic means characteristic of cyanosis, a condition where the skin appears blue due to low oxygen saturation in the tissues near the skin.

Eukaryotic (eu-kary-otic): Eukaryotic refers to cells that are characterized by having a truly defined nucleus. Animals, plants, protists, and fungi are examples of eukaryotic organisms.

Mitotic (mit-otic): Mitotic refers to the cell division process of mitosis. Somatic cells, or cells other than sex cells, reproduce by mitosis.

Narcotic (narc-otic): Narcotic refers to a class of addictive drugs that induce a state of stupor or euphoria.

Neurotic (neur-otic): Neurotic describes conditions that are related to nerves or a nerve disorder. It can also refer to a number of mental disorders that are characterized by anxiety, phobias, depression, and obsessive compulsive activity (neurosis).

Psychotic (psych-otic): Psychotic denotes a type of mental illness, called psychosis, that is characterized by abnormal thinking and perception.

Prokaryotic (pro-kary-otic): Prokaryotic means of or relating to single-celled organisms without a true nucleus. These organisms include bacteria and archaeans.

Symbiotic (sym-bi-otic): Symbiotic refers to relationships where organisms live together (symbiosis). This relationship may be beneficial to only one party or to both parties.

Zoonotic (zoon-otic): This term refers to a type of disease that can be transmitted from animals to people. The zoonotic agent may be a virusfungus, bacterium, or other pathogen.

The Names, Functions, and Locations of Cranial Nerves

Anatomy of the Brain

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Cranial Nerves
 The human cranial nerves and their areas of innervation. (Larger Image).Encyclopedia Britannica / UIG / Getty Images


By Regina BaileyUpdated on February 16, 2020

The cranial nerves are nerves that arise from the brain and exit the skull through holes (cranial foramina) at its base rather than through the spinal cord. Peripheral nervous system connections with various organs and structures of the body are established through cranial nerves and spinal nerves. While some cranial nerves contain only sensory neurons, most cranial nerves and all spinal nerves contain both motor and sensory neurons.

Key Takeaways

  • The body’s cranial nerves are nerves that come from the brain and exit the skull through the cranial foramina.
  • Cranial nerves control a variety of functions in the body including equilibrium control, eye movement, facial sensation, hearing, neck and shoulder movement, respiration, and tasting.
  • There are 12 paired cranial nerves that arise from the brainstem.
  • Aspects of vision, like peripheral vision, are under the control of the optic cranial nerve (II). Medical professionals can test visual acuity using a Snellen chart.
  • The trigeminal cranial nerve is the largest of the cranial nerves. It is involved in corneal reflex and facial sensation along with chewing.


Cranial nerves are responsible for the control of a number of functions in the body. Some of these functions include directing sense and motor impulses, equilibrium control, eye movement and vision, hearing, respiration, swallowing, smelling, facial sensation, and tasting. The names and major functions of these nerves are listed below.https://b4b8cd5e6ccf0f94a44fc2e8d997efff.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

  1. Olfactory Nerve: Sense of smell
  2. Optic Nerve: Vision
  3. Oculomotor Nerve: Eyeball and eyelid movement
  4. Trochlear Nerve: Eye movement
  5. Trigeminal Nerve: This is the largest cranial nerve and is divided into three branches consisting of the ophthalmic, maxillary and mandibular nerves. Functions controlled include facial sensation and chewing.
  6. Abducens Nerve: Eye movement
  7. Facial Nerve: Facial expressions and sense of taste
  8. Vestibulocochlear Nerve: Equilibrium and hearing
  9. Glossopharyngeal Nerve: Swallowing, sense of taste, and saliva secretion
  10. Vagus Nerve: Smooth muscle sensory and motor control in throat, lungsheart, and digestive system
  11. Accessory Nerve: Movement of neck and shoulders
  12. Hypoglossal Nerve: Movement of tongue, swallowing, and speech


The cranial nerves consist of 12 paired nerves that arise from the brainstem. The olfactory and optic nerves arise from the anterior portion of the brain called the cerebrum. The oculomotor and trochlear cranial nerves stem from the midbrain. The trigeminal, abducens, and facial nerves arise in the pons. The vestibulocochlear nerve arises in the inner ears and goes to the pons. The glossopharyngeal, vagus, accessory and hypoglossal nerves are attached to the medulla oblongata.

Sensory Cranial Nerves

Snellen chart
 Snellen chart test assesses visual acuity and optic nerve function. CentralITAlliance / iStock / Getty Images Plus

There are three sensory cranial nerves: olfactory (I), optic (II), and vestibulocochlear (VIII). These cranial nerves are responsible for our senses of smell, vision, hearing, and equilibrium. Medical professionals test cranial nerve I by having a person close their eyes and one nostril while inhaling a scent such as coffee or vanilla. An inability to recognize a scent may indicate problems with the sense of smell and cranial nerve I.1 The optic nerve (II) is responsible for transmitting visual information.2 Examiners test visual acuity using a Snellen chart.1https://b4b8cd5e6ccf0f94a44fc2e8d997efff.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Vestibulocochlear nerve (VIII) functions in hearing and can be assessed with the whisper test. The examiner stands behind the person and whispers a sequence of letters into one ear while the person holds a hand over the non-tested ear. The process is repeated with the opposite ear. Ability to repeat the whispered words indicates proper function.1https://b4b8cd5e6ccf0f94a44fc2e8d997efff.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Motor Cranial Nerves

Motor nerves function in movement of anatomical structures. Motor cranial nerves include the oculomotor (III), trochlear (IV), abducens (VI), accessory (XI), and hypoglossal (XII) nerves. Cranial nerves III, IV, and VI control eye movement, with the oculomotor nerve controlling pupil constriction.3 All three are assessed by asking a patient to use only their eyes to follow a moving target, such as a penlight or an examiner’s finger.1

The accessory nerve controls movement of the neck and shoulders. It is tested by having a person shrug his or her shoulders and turn their head from side to side against resistance from the the examiner’s hand.1 The hypoglossal nerve controls movement of the tongue, swallowing, and speech.4 Assessment of this nerve involves asking the person to stick out his or her tongue to ensure that it is midline.1https://b4b8cd5e6ccf0f94a44fc2e8d997efff.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Mixed Cranial Nerves

Trigeminal nerve
 The Trigeminal Nerve.  normaals / iStock / Getty Images Plus

Mixed nerves have both sensory and motor function. Mixed cranial nerves include the trigeminal (V), facial (VII), glossopharyngeal (IX), and vagus (X) nerves. The trigeminal nerve is the largest cranial nerve and is involved in facial sensation, chewing, and corneal reflex. Facial sensations are often checked by rubbing soft and blunt objects on various areas of the face.1 Chewing is typically tested by having the person open and close his or her mouth. The facial nerve controls facial expressions and is involved in taste sensation. This nerve is commonly tested by observing for facial symmetry.1 The glossopharyngeal nerve plays a role in swallowing, sense of taste, and saliva secretion. The vagus nerve is involved in smooth muscle sensory and motor control in the throat, lungs, heart, and digestive system. Cranial nerves IX and X are typically assessed together. The person is asked to say “ah” while the examiner observes movement of the palate.1 Swallowing ability and the ability to taste different foods are also tested.5

Biology Prefixes and Suffixes: -penia

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Credit: PASIEKA/Getty Images


By Regina BaileyUpdated on July 21, 2019

The suffix (-penia) means to lack or to have a deficiency. It is derived from the Greek penía for poverty or need. When added to the end of a word, (-penia) often indicates a specific type of deficiency.https://9ec2ac1a8bc410fc6e54b5a79d4bc447.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Words Ending With: (-penia)

  • Calcipenia (calci-penia): Calcipenia is the condition of having an insufficient amount of calcium in the body. Calcipenic rickets is commonly caused by a deficiency of vitamin D or calcium and results in the softening or weakening of bones.
  • Chloropenia (chloro-penia): A deficiency in the concentration of chloride in the blood is called chloropenia. It may result from a diet poor in salt (NaCl).
  • Cytopenia (cyto-penia): A deficiency in the production of one or more types of blood cells is called cytopenia. This condition may be caused by liver disorders, poor kidney function, and chronic inflammatory diseases.
  • Ductopenia (ducto-penia): Ductopenia is a reduction in the number of ducts in an organ, typically the liver or gall bladder.
  • Enzymopenia (enzymo-penia): The condition of having an enzyme deficiency is called enzymopenia.
  • Eosinopenia (eosino-penia): This condition is characterized by having abnormally low numbers of eosinphils in the blood. Eosinophils are white blood cells that become increasingly active during parasitic infections and allergic reactions.
  • Erythropenia (erythro-penia): A deficiency in the numbers of erythrocytes (red blood cells) in the blood is called erythropenia. This condition may result from blood loss, low blood cell production, or red blood cell destruction.
  • Granulocytopenia (granulo-cyto-penia): A significant decrease in the numbers of granulocytes in the blood is termed granulocytopenia. Granulocytes are white blood cells that include neutrophils, eosinophils, and basophils.
  • Glycopenia (glyco-penia): Glycopenia is sugar deficiency in an organ or tissue, usually caused by low blood sugar.
  • Kaliopenia (kalio-penia): This condition is characterized by having insufficient concentrations of potassium in the body.
  • Leukopenia (leuko-penia): Leukopenia is an abnormally low white blood cell count. This condition poses an increased risk in infection, as the immune cell count in the body is low.
  • Lipopenia (lipo-penia): Lipopenia is a deficiency in the number of lipids in the body.
  • Lymphopenia (lympho-penia): This condition is characterized by a deficiency in the number of lymphocytes in the blood. Lymphocytes are white blood cells that are important to cell-mediated immunity. Lymphocytes include B cells, T cells, and natural killer cells.
  • Monocytopenia (mono-cyto-penia): Having an abnormally low monocyte count in the blood is called monocytopenia. Monocytes are white blood cells that include macrophages and dendritic cells.
  • Neuroglycopenia (neuro-glyco-penia): Having a deficiency in glucose (sugar) levels in the brain is termed neuroglycopenia. Low glucose levels in the brain disrupts neuron function and if prolonged, can lead to tremors, anxiety, sweating, coma, and death.
  • Neutropenia (neutro-penia): Neutopenia is a condition characterized by having low numbers of infection-fighting white blood cells called neutrophils in the blood. Neutrophils are one of the first cells to travel to an infection site and actively kill pathogens.
  • Osteopenia (osteo-penia): The condition of having lower than normal bone mineral density, which may lead to osteoporosis, is called osteopenia.
  • Phosphopenia (phospho-penia): Having a phosphorus deficiency in the body is termed phosphopenia. This condition may result from an abnormal excretion of phosphorus by the kidneys.
  • Sarcopenia (sarco-penia): Sarcopenia is the natural loss of muscle mass associated with the aging process.
  • Sideropenia (sidero-penia): The condition of having abnormally low iron levels in the blood is known as sideropenia. This may result from blood loss or iron deficiency in the diet.
  • Thrombocytopenia (thrombo-cyto-penia): Thrombocytes are platelets, and thrombocytopenia is the condition of having an abnormally low platelet count in the blood.

Biology Prefixes and Suffixes: diplo-

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Gonorrhea Bacterium
 Conceptual visualization of the diplococcus bacterium gonorrhea (Neisseria gonorrhoeae) that causes the sexually transmitted disease gonorrhea. Credit: Science Picture Co/Subjects/Getty Images


By Regina BaileyUpdated on February 20, 2018

The prefix (diplo-) means double, twice as many or twice as much. It is derived from the Greek diploos meaning double.https://8dca76540a10e76060f9dd28898aa98e.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Words Beginning With: (Diplo-)

Diplobacilli (diplo-bacilli): This is the name given to rod-shaped bacteria that remain in pairs following cell division. They divide by binary fission and are joined end to end.

Diplobacteria (diplo-bacteria): Diplobacteria is the general term for bacteria cells that are joined in pairs.https://8dca76540a10e76060f9dd28898aa98e.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Diplobiont (diplo-biont): A diplobiont is an organism, such as a plant or fungus, that has both haploid and diploid generations in its life cyle.

Diploblastic (diplo-blastic): This term refers to organisms that have body tissues that are derived from two germ layers: the endoderm and ectoderm. Examples include cnidarians: jellyfish, sea anemones, and hydras.

Diplocardia (diplo-cardia): Diplocardia is a condition in which the right and left halves of the heart are separated by a fissure or groove.

Diplocardiac (diplo-cardiac): Mammals and birds are examples of diplocardiac organisms. They have two separate circulatory pathways for blood: pulmonary and systemic circuits.

Diplocephalus (diplo-cephalus): Diplocephalus is a condition in which a fetus or conjoined twins develop two heads.

Diplochory (diplo-chory): Diplochory is a method by which plants disperse seeds. This method involves two or more distinct mechanisms.

Diplococcemia (diplo-cocc-emia): This condition is characterized by the presence of diplococci bacteria in the blood.

Diplococci (diplo-cocci): Spherical or oval-shaped bacteria that remain in pairs following cell division are called diplococci cells.

Diplocoria (diplo-coria): Diplocoria is a condition that is characterized by the occurrence of two pupils in one iris. It may result from eye injury, surgery, or it may be congenital.

Diploe (diploe): Diploe is the layer of spongy bone between the inner and outer bone layers of the skull.

Diploid (diplo-id): A cell that contains two sets of chromosomes is a diploid cell. In humans, somatic or body cells are diploid. Sex cells are haploid and contain one set of chromosomes.

Diplogenic (diplo-genic): This term means producing two substances or having the nature of two bodies.

Diplogenesis (diplo-genesis): The double formation of a substance, as seen in a double fetus or a fetus with double parts, is known as diplogenesis.

Diplograph (diplo-graph): A diplograph is an instrument that can produce double writing, such as embossed writing and normal writing at the same time.

Diplohaplont (diplo-haplont): A diplohaplont is an organism, such as algae, with a life cycle that alternates between fully developed haploid and diploid forms.

Diplokaryon (diplo-karyon): This term refers to a cell nucleus with double the diploid number of chromosomes. This nucleus is polyploid meaning that it contains more than two sets of homologous chromosomes.

Diplont (diplo-nt): A diplont organism has two sets of chromosomes in its somatic cells. Its gametes have a single set of chromosomes and are haploid.

Diplopia (diplo-pia): This condition, also known as double vision, is characterized by seeing a single object as two images. Diplopia can occur in one eye or both eyes.

Diplosome (diplo-some): A diplosome is a pair of centrioles, in eukaryotic cell division, that aids in spindle apparatus formation and organization in mitosis and meiosis. Diplosomes are not found in plant cells.

Diplozoon (diplo-zoon): A diplozoon is a parasitic flatworm that fuses together with another of its kind and the two exist in pairs.

Biology Prefixes and Suffixes: arthr- or arthro-

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Arthritis X-ray
 Arthritis is an inflammation of the joints. This colored X-ray shows the hands of an 81 year old female patient with rheumatoid arthritis. Credit: Science Photo Library/Getty Images


By Regina BaileyUpdated on September 06, 2019

The prefix (arthr- or arthro-) means a joint or any junction between two different parts. Arthritis is a condition characterized by joint inflammation.https://67e08aa87be82026012b7dfffcdc80b8.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Words Beginning With “Arthr”

Dictionary.com notes that “arthr” comes from the Greek term “árthron,” which, as noted, means “a joint.” This section contains terms that begin with “arthr” but are followed by a vowel other than “o.”https://67e08aa87be82026012b7dfffcdc80b8.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Arthralgia (Arthr – Algia)

Pain of the joints. It is a symptom rather than a disease and can result from injury, allergic reaction, infection, or disease. Arthralgia occurs commonly in the joints of the hands, knees, and ankles.

Atherectomy (Arthr – Ectomy)

The surgical excision (cutting out) of a joint.

Arthrempyesis (Arthr – Empyesis)

Formation of pus in a joint. It is also known as arthropyosis and occurs when the immune system has difficulty eliminating the source of infection or inflammation.

Arthresthesia (Arthr – Esthesia)

Sensation in the joints.

Arthritides (Arthr – Itides)

Plural form of arthritis.

Arthritis (Arthr – Itis)

Inflammation of the joints. Symptoms of arthritis include pain, swelling, and joint stiffness. Types of arthritis include gout and rheumatoid arthritis. Lupus can also cause inflammation in joints as well as in a variety of different organs.https://67e08aa87be82026012b7dfffcdc80b8.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Words Beginning With “Arthro”

The prefix “arthro” also derives from the Greek “árthron.” To ease study and memorization, this section is comprised of terms that begin with “arthro.”

Arthrosis (Arthr – Osis):

A degenerative joint disease commonly caused by deterioration of the cartilage around a joint. This condition affects people as they age.

Arthrotomy (Arthr – Otomy)

A surgical procedure in which an incision is made in a joint for the purpose of examining and repairing it.https://67e08aa87be82026012b7dfffcdc80b8.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Arthrocele (Arthro – Cele)

An older medical term that indicates the swelling of a joint. It can also indicate a synovial membrane hernia.

Arthroderm (Arthro – Derm)

The outer covering, shell, or exoskeleton of an arthropod. An arthroderm has a number of joints attached to muscle allowing for movement and flexibility.

Arthrodesis (Arthro – Desis)

A surgical procedure that involves the fixation of a joint in order to promote the fusion of bone. It is typically used to treat chronic pain.

Arthrofibrosis (Arthro – Fibrosis)

The formation of scar tissue due to some trauma or injury within a joint. The scar tissue inhibits overall joint movement.

Arthrogram (Arthro – Gram)

X-ray, fluoroscopy, or MRI used to examine the interior of a joint. An arthrogram is used to diagnose problems such as tears in joint tissues.

Arthrogryposis (Arthro – Gryp – Osis)

A congenital joint disorder in which a joint or joints lack the normal range of motion and may be stuck in one position.

Arthrokinetic (Arthro – Kinetic)

A physiological term of or relating to joint movement.

Arthrology (Arthro – Logy)

A branch of anatomy that focuses on the structure and function of the joints.

Arthrolysis (Arthro – Lysis)

A type of surgery performed to repair stiff joints. Arthrolysis involves the loosening of joints that have become stiff due to injury or as a result of a disease such as osteoarthritis. As (arthro-) refers to a joint, (-lysis) means to split, cut, loosen, or untie.

Arthromere (Arthro – Mere)

Any of the body segments of an arthropod or animal with jointed limbs.

Arthrometer (Arthro – Meter)

An instrument used to measure the range of motion in a joint.

Arthropathy (Arthro – Pathy)

Any disease affecting the joints. Such diseases include arthritis and gout. Facet arthropathy occurs in the joints of the spine, enteropathic arthropathy occurs in the colon, and neuropathic arthropathy results from nerve damage associated with diabetes.

Arthropod (Arthro – Pod)

Animals of the phylum Arthropoda that have a jointed exoskeleton and jointed legs. Among these animals are spiders, lobsters, ticks and other insects.

Arthropodan (Arthro – Podan)

Of or relating to arthropods.

Arthrosclerosis (Arthro – Scler – Osis)

A condition characterized by hardening or stiffening of the joints. As we age, joints may harden and become stiff affecting joint stability and flexibility.

Arthroscope (Arthro – Scope)

An endoscope used for examining the inside of a joint. This instrument consists of a thin, narrow tube attached to a fiber optic camera that is inserted into a small incision near a joint.

Arthroscopy (Arthro – Scopy)

Surgery or procedure which entails using an arthroscope to visualize the interior of a joint. The purpose of the procedure is to examine or treat the joint in question.

Arthrospore (Arthro – Spore)

A fungal or algal cell resembling a spore that is produced by segmentation or breaking of the hyphae. These asexual cells are not true spores and similar cells are produced by some bacteria.

Biology Prefixes and Suffixes Index

You can easily understand scientific terms through prefixes and suffixes

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closeup of hands on dictionary
beemore/E+/Getty Images


By Regina BaileyUpdated on April 21, 2019

Have you ever heard of pneumonoultramicroscopicsilicovolcanoconiosis? This is an actual word, but don’t let that scare you. Some science terms can be difficult to comprehend: By identifying the affixes — elements added before and after base words — you can understand even the most complex terms. This index will help you identify some commonly used prefixes and suffixes in biology.https://227ac1b5c112bd5e22f9dbffc46922f0.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Common Prefixes

(Ana-): indicates upward direction, synthesis or buildup, repetition, excess or separation.https://227ac1b5c112bd5e22f9dbffc46922f0.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

(Angio-): signifies a type of receptacles such as a vessel or shell.

(Arthr- or Arthro-): refers to a joint or a junction that separates different parts.

(Auto-): identifies something as belonging to oneself, occurring within or occurring spontaneously.

(Blast- , -blast): indicates an immature developmental stage.

(Cephal- or Cephalo-): referring to the head.

(Chrom- or Chromo-): denotes color or pigmentation.

(Cyto- or Cyte-): regarding or relating to a cell.

(Dactyl-, -dactyl): refers to a digit or tactile appendages such as a finger or toe.

(Diplo-): means double, paired or twofold.

(Ect- or Ecto-): means outer or external.

(End- or Endo-): means inner or internal.

(Epi-): indicates a position that is above, on or near a surface.https://227ac1b5c112bd5e22f9dbffc46922f0.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

(Erythr- or Erythro-): means red or reddish in color.

(Ex- or Exo-): means external, out of or away from.

(Eu-): means genuine, true, well or good.

(Gam-, Gamo or -gamy): refers to fertilization, sexual reproduction or marriage.

(Glyco- or Gluco-): pertains to a sugar or a sugar derivative.

(Haplo-): means single or simple.

(Hem-, Hemo- or Hemato-): denoting blood or blood components (plasma and blood cells).

(Heter- or Hetero-): means unlike, different or other.

(Karyo- or Caryo-): means nut or kernel, and also refers to the nucleus of a cell.

(Meso-): means middle or intermediate.https://227ac1b5c112bd5e22f9dbffc46922f0.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

(My- or Myo-): means muscle.

(Neur- or Neuro-): referring to nerves or the nervous system.

(Peri-): means surrounding, near or around.

(Phag- or Phago-): pertaining to eating, swallowing or consuming.

(Poly-): means many or excessive.

(Proto-): means primary or primitive.

(Staphyl- or Staphylo-): referring to a cluster or bunch.

(Tel- or Telo-): denoting an end, extremity or final phase.

(Zo- or Zoo-): pertaining an animal or animal life.

Common Suffixes

(-ase): denoting an enzyme. In enzyme naming, this suffix is added to the end of the substrate name.

(-derm or -dermis): referring to tissue or skin.

(-ectomy or -stomy): pertaining to the act of cutting out or the surgical removal of tissue.

(-emia or -aemia): referring to a condition of the blood or the presence of a substance in the blood.

(-genic): means giving rise to, producing or forming.

(-itis): denoting inflammation, commonly of a tissue or organ.

(-kinesis or -kinesia): indicating activity or movement.

(-lysis): referring to degradation, decomposition, bursting or releasing.

(-oma): indicating an abnormal growth or tumor.

(-osis or -otic): indicating a disease or abnormal production of a substance.

(-otomy or -tomy): denoting an incision or surgical cut.

(-penia): pertaining to a deficiency or lack.

(-phage or -phagia): the act of eating or consuming.

(-phile or -philic): having an affinity for or strong attraction to something specific.

(-plasm or -plasmo): referring to tissue or a living substance.

(-scope): denoting an instrument used for observation or examination.

(-stasis): indicating the maintenance of a constant state.

(-troph or -trophy): pertaining to nourishment or a method of nutrient acquisition.

Other Tips

While knowing suffixes and prefixes will tell you much about biological terms, it’s helpful to know a few other tricks for deciphering their meanings, including:

  • Breaking down words: Breaking down biological terms into their component parts can help you decipher their meanings.
  • Dissections: Just as you might dissect a frog “to separate (it) into pieces,” as Merriam-Webster explains, you can also break down a biological term to “expose” its “several parts for scientific examination.”

Biology Prefixes and Suffixes: meso-

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 Mesothelium is simple squamous epithelium derived from the middle embryonic germ layer known as the mesoderm. It is sometimes called pavement epithelium as the cells are analogous to flat tiles on a floor. Credit: Ed Reschke/Photolibrary/Getty Images


By Regina BaileyUpdated on January 09, 2018

The prefix (meso-) comes from the Greek mesos or middle. (Meso-) means middle, between,  intermediate, or moderate. In biology, it commonly used to indicate a middle tissue layer or body segment.

Words Beginning With: (meso-)

Mesoblast (meso-blast): The mesoblast is the middle germ layer of an early embryo. It contains cells that will develop into the mesoderm.https://5e0c26d6476101fcc164fb08b9fdbb53.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Mesocardium (meso-cardium): This double layer membrane supports the embryonic heart. Mesocardium is a temporary structure that attaches the heart to the body wall and foregut.

Mesocarp (meso-carp): The wall of fleshy fruit is known as pericarp and contains three layers. Mesocarp is the middle layer of the wall of ripened fruit. Endocarp is the inner most layer and exocarp is the outer most layer.

Mesocephalic (meso-cephalic): This term refers to having a head size of medium proportions. Organisms with a mesocephalic head size range between 75 and 80 on the cephalic index.

Mesocolon (meso-colon): The mesocolon is part of the membrane called the mesentery or middle bowel, that connects the colon to the abdominal wall.

Mesoderm (meso-derm): Mesoderm is the middle germ layer of a developing embryo that forms connective tissues such as musclebone, and blood. It also forms urinary and genital organs including the kidneys and gonads.

Mesofauna (meso-fauna): Mesofauna are small invertebrates that are intermediate-sized microbes. This includes mites, nematodes, and springtails ranging in size from 0.1 mm to 2 mm.https://5e0c26d6476101fcc164fb08b9fdbb53.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Mesogastrium (meso-gastrium): The middle region of the abdomen is called the mesogastrium. This term also refers to the membrane that supports the embryonic stomach.

Mesoglea (meso-glea): Mesoglea is the layer of gelatinous material located between outer and inner cell layers in some invertebrates including jellyfish, hydra, and sponges. This layer is also called mesohyl.

Mesohyloma (meso-hyl-oma): Also known as mesothelioma, mesohyloma is an aggressive type of cancer originating from epithelium derived from the mesoderm. This form of cancer occurs commonly in the lining of the lungs and is associated with asbestos exposure.

Mesolithic (meso-lithic): This term refers to the middle stone age period between the Paleolithic and Neolithic eras. The use of stone tools called microliths became prevalent among ancient cultures in the Mesolithic age.

Mesomere (meso-mere): A mesomere is a blastomere (cell resulting from the cell division or cleavage process that occurs following fertilization) of medium size.

Mesomorph (meso-morph): This term describes an individual with a muscular body build predominated by tissue derived from the mesoderm. These individuals gain muscle mass relatively quickly and have minimal body fat.

Mesonephros (meso-nephros): The mesonephros is the middle portion of the embryoinc kidney in vertebrates. It develops into adult kidneys in fish and amphibians, but is transformed into reproductive structures in higher vertebrates.

Mesophyll (meso-phyll): Mesophyll is the photosynthetic tissue of a leaf, located between the upper and lower plant epidermisChloroplasts are located in the plant mesophyll layer.

Mesophyte (meso-phyte): Mesophytes are plants living in habitats that provide a moderate supply of water. They are found in open fields, meadows, and shady areas that are not too dry or too wet.

Mesopic (mes-opic): This term refers to having vision in moderate levels of light. Both rods and cones are active at the mesopic range of vision.

Mesorrhine (meso-rrhine): A nose that is of moderate width is considered to be mesorrhine.

Mesosome (meso-some): The anterior portion of the abdomen in arachnids, located between the cephalothorax and lower abdomen, is called the mesosome.

Mesosphere (meso-sphere): The mesosphere is Earth’s atmospheric layer located between the stratosphere and thermosphere.

Mesosternum (meso-sternum): The middle region of the sternum, or breastbone is called the mesosternum. The sternum connects the ribs forming the rib cage, which protects the organs of the chest.

Mesothelium (meso-thelium): Mesothelium is epithelium (skin) that is derived from the mesoderm embryonic layer. It forms simple squamous epithelium.

Mesothorax (meso-thorax): The middle segment of an insect located between the prothorax and metathorax is the mesothorax.

Mesotrophic (meso-trophic): This term refers commonly to a body of water with moderated levels of nutrients and plants. This intermediate stage is between the oligotrophic and eutrophic stages.

Mesozoa (meso-zoa): These free-living, worm-like parasites inhabit marine invertebrates such as flatworms, squid, and star fish. The name mesozoa means middle (meso) animal (zoon), as these creatures were once thought to be intermediates between protists and animals.

Biology Prefixes and Suffixes: Aer- or Aero-

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Pollen in Wind
 Timothy grass (Phleum pratense) pollen being blown by wind. Pollen and dust are examples of aeroallergens. They are airborne particles that can induce an allergic reaction. Pal Hermansen/The Image Bank/Getty Images


By Regina BaileyUpdated on September 09, 2019

The prefix (aer- or aero-) refers to air, oxygen, or a gas. It comes from the Greek aer meaning air or referring to the lower atmosphere.https://0af15e91c12c36b3a22abdf800c64162.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Words Beginning with “Aer-” Or “Aero-“

The following are words that begin with “aer-” or “aero-.” Each word is listed, followed by the syllabification, with the definition below each term.

Aerate (Aer – Ate)

To expose to air circulation or to gas. It may also refer to supplying blood with oxygen as occurs in respiration.

Aerenchyma (Aer – En – Chyma)

Specialized tissue in some plants that form gaps or channels that allow air circulation between the roots and shoot. This tissue is commonly found in aquatic plants.

Aeroallergen (Aero – Aller – Gen)

A small airborne substance (pollen, dust, spores, etc.) that can enter the respiratory tract and induce an immune response or allergic reaction.

Aerobe (Aer – Obe)

An organism that requires oxygen for respiration and can only exist and grow in the presence of oxygen.

Aerobic (Aer – O – Bic)

Means occurring with oxygen and commonly refers to aerobic organisms. Aerobes require oxygen for respiration and can only live in the presence of oxygen.

Aerobiology (Aero – Biology)

The study of both living and nonliving constituents of the air that can induce an immune response. Examples of airborne particles include dust, fungialgae, pollen, insects, bacteriaviruses, and other pathogens.

Aerobioscope (Aero – Bio – Scope)

An instrument used to collect and analyze air to determine its bacterial count.

Aerocele (Aero – Cele)

The build up of air or gas in a small natural cavity. These formations may develop into cysts or tumors in the lungs.

Aerococcus (Aero – Coccus)

A genus of airborne bacteria first identified in air samples. They are part of the normal flora of bacteria that live on the skin.

Aerocoly (Aero – Coly)

A condition characterized by the accumulation of gas in the colon.

Aerodermectasia (Aero – Cerm – Ectasia)

A condition characterized by the accumulation of air in subcutaneous (under the skin) tissue. Also called subcutaneous emphysema, this condition may develop from a ruptured airway or air sac in the lungs.

Aerodontalgia (Aero – Dont – Algia)

Tooth pain that develops due to changes in atmospheric air pressure. It is often associated with flying at high altitudes.

Aeroembolism (Aero – Embol – Ism)

blood vessel obstruction caused by air or gas bubbles in the cardiovascular system.

Aerogastralgia (Aero – Gastr – Algia)

Stomach pain resulting from excess air in the stomach.

Aerogen (Aero – Gen)

A bacterium or microbe that produces gas.

Aeromagnetics (Aero – Magnetics)

The scientific study of the earth’s magnetic attributes based on atmospheric conditions.

Aeromedicine (aAero – Medicine)

The study of disorders, both psychologically and physiologically based, having to do with flight.

Aerometer (Aer – O – Meter)

A device that can determine both the density and the weight of air.

Aeronomy (Aer – Onomy)

The scientific field of study that deals with the physical and chemical properties of earth’s upper atmosphere.

Aeroparotitis (Aero – Parot – Itis)

Inflammation or swelling of the parotid glands resulting from the abnormal presence of air. These glands produce saliva and are located around the mouth and throat area.

Aeropathy (Aero – Pathy)

A general term referring to any sickness resulting from a change in atmospheric pressure. It is sometimes called air sickness, altitude sickness, or decompression sickness.

Aerophagia (Aero – Phagia)

The act of swallowing excessive amounts of air. This can lead to digestive system discomfort, bloating, and intestinal pain.

Aerophore (Aero – Phore)

A device that supplies air where there is no available oxygen. Such devices can be used to help trapped miners.

Aerophyte (Aer – O – Phyte)

Synonym for epiphyte. Aerophytes are plants that depend on other plants for their structural support but not for their nutrients.

Anaerobe (An – Aer – Obe)

An organism that does not require oxygen for respiration and can exist in the absence of oxygen. Facultative anaerobes can live and develop with or without oxygen. Obligate anaerobes can live only in the absence of oxygen.

Anaerobic (An – Aer – O – Bic)

Means occurring without oxygen and commonly refers to anaerobic organisms. Anaerobes, such as some bacteria and archaeans, live and grow in the absence of oxygen.

Anaerobiosis (An – Aer – O – Biosis)

Any of a number of forms of life that can survive without air/oxygen.

White Matter and Your Brain

White Matter Function and Disorders

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Brain White Matter
 This is an anterior angled view of a sectioned human brain. The left hemisphere of the brain has been sectioned to reveal the white matter. MedicalRF.com/Getty Images


By Regina BaileyUpdated on August 06, 2019

The brain’s white matter is situated under the surface gray matter or cerebral cortex of the brain. White matter is composed of nerve cell axons, which extend from the neuron cell bodies of gray matter. These axon fibers form connections between nerve cells. White matter nerve fibers serve to connect the cerebrum with different areas of the brain and spinal cord.https://6af92bd2158b3d7e9c04b3f5372f91ea.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

White matter contains nerve fibers that are wrapped with nervous tissue cells known as neuroglia. Neuroglia called oligodendrocytes form an insulating coat or myelin sheath that wraps around neuronal axons. The myelin sheath is composed of lipids and proteins and functions to speed up nerve impulses. White brain matter appears white due to its high composition of myelinated nerve fibers. It is the lack of myelin in the neuronal cell bodies of the cerebral cortex that makes this tissue appear gray.https://6af92bd2158b3d7e9c04b3f5372f91ea.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Most of the subcortical region of the brain is composed of white matter with masses of gray matter dispersed throughout. Conglomerates of gray matter that are located below the cortex include the basal gangliacranial nerve nuclei, and midbrain structures such as the red nucleus and substantia nigra.

Key Takeaways: What Is White Matter?

  • White matter of the brain is situated beneath the outer cortex layer, also known as gray matter. Most of the brain is composed of white matter.
  • White brain matter appears white because of myelin that is wrapped around the nerve axons of white matter. Myelin helps to facilitate nerve impulse transmission.
  • White matter nerve fibers connect the cerebrum with the spinal cord and other areas of the brain.
  • There are three main types of white matter nerve fiber tracts: commissural fibers, association fibers, and projection fibers.
  • Commissural fibers connect corresponding regions of the left and right hemispheres of the brain.
  • Association fibers connect brain regions within the same hemisphere.
  • Projection fibers connect the cerebral cortex to the brainstem and spinal cord.

White Matter Fiber Tracts

The primary function of the brain’s white matter is to provide a pathway for connecting the different areas of the brain. Should this brain matter become damaged, the brain can rewire itself and establish new nerve connections between gray and white matter. White matter axon bundles of the cerebrum are composed of three main types of nerve fiber tracts: commissural fibers, association fibers, and projection fibers.https://6af92bd2158b3d7e9c04b3f5372f91ea.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

White Matter Nerve Pathways
 This is a colored 3-dimensional magnetic resonance imaging (MRI) scan of the white matter pathways of the brain, side view. White matter is composed of myelin-coated nerve cell fibers. Tom Barrick, Chris Clark, SGHMS/ Science Photo Library / Getty Images Plus

Commissural Fibers

Commissural fibers connect corresponding regions of the left and right brain hemispheres.

  • Corpus Callosum – thick bundle of fibers located within the medial longitudinal fissure (separates the brain hemispheres). The corpus callosum connects the left and right frontal lobestemporal lobes, and occipital lobes.
  • Anterior Commissure – small fiber bundles that make connections between the temporal lobes, olfactory bulbs, and amygdalae. The anterior commissure forms the anterior wall of the third ventricle and is thought to be involved in pain sensation.
  • Posterior Commissure – white matter fibers that cross the upper region of the cerebral aqueduct and interconnect the pretectal nuclei. These nuclei are involved in pupillary light reflex and control the diameter of the pupils in response to intense changes in light.
  • Fornix – an arching band of nerve fibers that connect the hippocampus in each brain hemisphere. The fornix also connects the hippocampus to the mamillary body of the hypothalamus and projects to the anterior nuclei of thalamus. It is a structure of the limbic system and is important to the transfer of information between the hemispheres of the brain.
  • Habenular Commissure – band of nerve fibers located in the diencephalon that are positioned in front of the pineal gland and connect the habenular nucleus of each brain hemisphere. Habenular nuclei are nerve cells of the epithalamus and a component of the limbic system.

Association Fibers

Association fibers connect cortex regions within the same hemisphere. There are two types of association fibers: short and long fibers. Short association fibers can be found just below the cortex and deep within white matter. These fibers connect brain gyri. Long association fibers connect cerebral lobes within brain regions.

  • Cingulum – band of fibers located within the cingulate gyrus that connect the cingulate gyrus and frontal lobes with the gyri of the hippocampus (also called parahippocampal gyri).
  • Arcuate Fasciculus – long association fiber tracts that connect frontal lobe gyri with the temporal lobe.
  • Dorsal Longitudinal Fasciculus – thin fiber tracts that connect the hypothalamus with portions of the midbrain.
  • Medial Longitudinal Fasciculus – fiber tracts that connect areas of the mesencephalon with cranial nerves that control eye muscles (oculomotor, trochlear, and abducent cranial nerves) and with spinal cord nuclei in the neck.
  • Superior Longitudinal Fasciculus – long association fiber tracts that connect the temporal, frontal, and occipital lobes.
  • Inferior Longitudinal Fasciculus – long association fiber tracts that connect the occipital and temporal lobes.
  • Occipitofrontal Fasciculus – association fibers that branch into superior and inferior tracts that connect the occipital and frontal lobes.
  • Uncinate Fasciculus – long association fibers that connect the frontal and temporal lobes of the cortex.

Projection Fibers

Projection fibers connect the cerebral cortex to the brainstem and spinal cord. These fiber tracts help to relay motor and sensory signals between the central nervous system and peripheral nervous system.

White Matter Disorders

Multiple Sclerosis
 In multiple sclerosis or MS, the nerves of the brain and spinal cord are damaged by one’s own immune system. Damage to myelin disrupts nerve signal transmission. ttsz / iStock / Getty Images Plus

White matter brain disorders typically result from abnormalities related to the myelin sheath. A lack or loss of myelin disrupts nerve transmissions and causes neurological problems. A number of diseases can affect white matter including multiple sclerosis, dementia, and leukodystrophies (genetic disorders that result in abnormal development or destruction of white matter). Destruction of myelin or demyelination can also result from inflammation, blood vessel problems, immune disorders, nutritional deficiencies, stroke, poisons, and certain drugs.

The Biology Suffix -lysis

Kidney Dialysis
Science Photo Library/Brand X Pictures/Getty Images

The suffix (-lysis) refers to decomposition, dissolution, destruction, loosening, breaking down, separation, or disintegration.


Analysis (ana-lysis): method of study involving the separation of material into its constituent parts.

Autolysis (auto-lysis): the self-destruction of tissue typically due to the production of certain enzymes within cells.

Bacteriolysis (bacterio-lysis): the destruction of bacterial cells.

Biolysis (bio-lysis): the death of an organism or tissue by dissolution. Biolysis also refers to the decomposition of living material by microorganisms such as bacteria and fungi.

Catalysis (cata-lysis): the action of a catalyst to accelerate a chemical reaction.

Chemolysis (chemo-lysis): decomposition of organic substances through the use of chemical agents.

Chromatolysis (chromat-o-lysis): the dissolution or destruction of chromatin.

Cytolysis (cyto-lysis): the dissolution of cells by the destruction of the cell membrane.

Dialysis (dia-lysis): the separation of smaller molecules from larger molecules in a solution by the selective diffusion of substances across a semi-permeable membrane. Dialysis is also a medical procedure done to separate metabolic waste, toxins and excess water from the blood.

Electrodialysis (electro-dia-lysis): the dialysis of ions from one solution to another through the use of an electric

Electrolysis (electro-lysis): method of destroying tissue, such as hair roots, by the use of an electrical current. It also refers to a chemical change, specifically decomposition, that is caused by an electric current.

Fibrinolysis (fibrin-o-lysis): a natural occurring process involving the break down of fibrin in blood clots through enzyme activity. Fibrin is a protein that forms a network to trap red blood cells and platelets.

Glycolysis (glyco-lysis): process in cellular respiration that results in the break down of sugar in the form of glucose for the harvesting of energy in the form of ATP.

Hemolysis (hemo-lysis): destruction of red blood cells as a result of cell rupture.

Heterolysis (hetero-lysis): the dissolution or destruction of cells from one species by the lytic agent from a different species.

Histolysis (histo-lysis): the breakdown or destruction of tissues.

Homolysis (homo-lysis): the dissolution of a molecule or cell into two equal parts, such as the formation of daughter cells in mitosis.

Hydrolysis (hydro-lysis): the decomposition of compounds or biological polymers into smaller molecules by a chemical reaction with water.

Paralysis (para-lysis): the loss of voluntary muscle movement, function, and sensation that causes the muscles to become loose or flaccid.

Photolysis (photo-lysis): decomposition caused by light energy. Photolysis plays a crucial role in photosynthesis by splitting water to produce oxygen and high energy molecules which are used to synthesize sugar.

Plasmolysis (plasmo-lysis): shrinkage that typically occurs in the cytoplasm of plant cells due to the flow of water outside of the cell by osmosis.

Pyrolysis (pyro-lysis): the decomposition of chemical compounds due to exposure to high temperatures.

Radiolysis (radio-lysis): the decomposition of chemical compounds due to exposure to radiation.

What Is AP Biology?

High school students using a microscope
Corbis / Getty Images / Getty Images

AP Biology is a course taken by high school students in order to gain credit for introductory college-level biology courses. Taking the course itself is not enough to gain college-level credit. Students enrolled in the AP Biology course must also take the AP Biology exam. Most colleges will give credit for entry-level biology courses for students who earn a score of 3 or better on the exam.https://21a5528f234869d9d289e83bf32215f4.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

The AP Biology course and exam are offered by the College Board. This examination board manages standardized tests in the United States. In addition to Advanced Placement tests, the College Board also manages the SAT, PSAT, and College-Level Examination Program (CLEP) tests.https://21a5528f234869d9d289e83bf32215f4.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

Enrolling in an AP Biology Course

Enrollment in this course is dependent upon the qualifications set up by your high school. Some schools may only allow you to enroll in the course if you have taken and performed well in prerequisite classes. Others may allow you to enroll in the AP Biology course without taking prerequisite classes. Talk to your school counselor about the necessary steps to take to enroll in the course. It is important to note that this course is fast-paced and designed to be at a college level. Anyone wishing to take this course should be prepared to work hard and spend time in class, as well as outside of class, in order to do well in this course.

Topics in an AP Biology Course

The AP Biology course will cover several biology topics. Some topics in the course and the exam will be covered more extensively than others. Topics covered in the course include, but are not limited to:

  • Cells and Cellular Reactions
  • Genetics and Heredity
  • Molecular Biology
  • Anatomy and Physiology
  • Evolution
  • Ecology


The AP Biology course includes 13 lab exercises that are designed to aid in your understanding and mastery of the topics covered in the course. Topics covered in the labs include:

  • Lab 1: Artificial Selection
  • Lab 2: Mathematical Modeling
  • Lab 3: Comparing DNA Sequences
  • Lab 4: Diffusion & Osmosis
  • Lab 5: Photosynthesis
  • Lab 6: Cell Respiration
  • Lab 7: Cell Division: Mitosis & Meiosis
  • Lab 8: Biotechnology: Bacterial Transformation
  • Lab 9: Biotechnology: Restriction Enzyme Analysis of DNA
  • Lab 10: Energy Dynamics
  • Lab 11: Transpiration
  • Lab 12: Fruit Fly Behavior
  • Lab 13: Enzyme Activity

AP Biology Exam

The AP Biology exam itself lasts about three hours and contains two sections. Each section counts for 50% of the exam grade. The first section includes multiple-choice and grid-in questions. The second section contains eight essay questions: two long and six short free-response questions. There is a required reading period before the student can begin writing the essays.

The grading scale for this exam is from 1 to 5. Earning credit for a college-level biology course depends on the standards set by each individual institution, but typically a score of 3 to 5 will be sufficient to gain credit.

Biology Prefixes and Suffixes: epi-

Epidermis (skin surface). This is a colored scanning electron micrograph (SEM) of the surface of the skin of a 6-year-old. The outermost surface of the epidermis is composed of dead and dying skin cells from the underlying epidermis, which help to protect the delicate epidermal cells from the external environment.
Science Photo Library/Getty Images

The prefix (epi-) has several meanings including on, upon, above, upper, in addition to, near, besides, following, after, outermost, or prevalent.


  • Epiblast (epi-blast): the outermost layer of an embryo in an early stage of development, prior to the formation of germ layers. The epiblast becomes the ectoderm germ layer which forms skin and nervous tissue.
  • Epicardium (epi-cardium): the innermost layer of the pericardium (a fluid-filled sac that surrounds the heart) and the outermost layer of the heart wall.
  • Epicarp (epi-carp): the outermost layer of the walls of a ripened fruit; outer skin layer of fruit. It is also called the exocarp.
  • Epidemic (epi-demic): an outbreak of disease that is prevalent or widespread throughout a population.
  • Epiderm (epi-derm): the epidermis or outer skin layer.
  • Epididymis (epi-didymis): a convoluted tubular structure that is situated upon the upper surface of male gonads (testes). The epididymis receives and stores immature sperm and houses mature sperm.
  • Epidural (epi-dural): a directional term that means on or outside of the dura mater (outermost membrane covering the brain and spinal cord). It is also an anesthetic injection into the space between the spinal cord and dura mater.
  • Epifauna (epi-fauna): aquatic animal life, such as starfish or barnacles, that live on the bottom surface of a lake or sea.
  • Epigastric (epi-gastric): pertaining to the upper middle region of the abdomen. It also means lying on or over the stomach.
  • Epigene (epi-gene): occurring or originating at or near the earth’s surface.
  • Epigeal (epi-geal): referring to an organism that lives or grows near or on the ground surface.
  • Epiglottis (epi-glottis): the thin flap of cartilage that covers the opening of the windpipe to prevent food from entering the opening during swallowing.
  • Epiphyte (epi-phyte): a plant that grows on the surface of another plant for support.
  • Episome (epi-some): DNA strand, typically in bacteria, that is either integrated in the host DNA or exists independently in the cytoplasm.
  • Epistasis (epi-stasis): describes the action of a gene upon another gene.
  • Epithelium (epi-thelium): animal tissue that covers the outside of the body and lines organs, vessels (blood and lymph), and cavities.
  • Epizoon (epi-zoon): an organism, such as a parasite, that lives on the body of another organism.



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