Study Guide

Taxonomy Terms

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Taxonomy Terms


Organisms that can create complex organic molecules from simple inorganic molecules found in their environments. They are also called producers, meaning they produce their own food. Think of them as producing from scratch the bricks and boards needed to build a house, which is our analogy here for a cell. Based on their energy source for completing this task, they are categorized as photoautotrophs or chemoautotrophs. Contrast autotrophs with heterotrophs.

Binomial Nomenclature

The system we use to identify each unique species by a distinct, two-word name. The name is always italicized and written in Latin. The first word is the genus of the organism and is capitalized; the second word designates the particular species. Don't be fooled. The species name is actually both words together, not the second word alone. (Compare species identifier and species name below.) You are a member of the species Homo sapiens. Another member of our species, Carl Linnaeus, developed this system.


The opening in an embryo created very early in development through a process called gastrulation. Before gastrulation, the embryo is called a blastula and consists of a ball of cells of two types: cells on the outside (ectoderm) and cells on the inside (endoderm). Some of the cells in the outer layer of the blastula move inward. (Imagine pushing your finger into a poorly inflated balloon.) This creates a tube with an opening. This opening is the blastopore. Groups of animals are defined by whether their blastopore becomes their mouth or their anus later in development. It will become the mouth in protostomes and the anus in deuterostomes.


An early stage in animal development. After an egg is fertilized, the single cell that results (a zygote) begins to divide. At first, it is a solid ball of cells. Then it becomes a hollow sphere as the inside becomes filled with fluid (a.k.a. blastocoel). This hollow sphere of cells is the blastula. Its next stage of development is gastrulation. In mammals, the blastula is a little bit different and is called a blastocyst.


Autotrophs that get their energy through chemical reactions that use inorganic molecules.


Heterotrophs that get their energy through chemical reactions that use inorganic molecules.


Organisms, including bacteria, which get all their energy through biological reactions, like moving electrons around. When they get a little low on energy, they're not looking to call the local pizza place.


A class of animals that are deuterostomes. At some point in their development, they have a notochord, which is where the word chordate comes from. A notochord is a rod made of cartilage that runs the length of the animal and acts as a skeleton. In vertebrates, it is replaced by bony vertebrae later in development. Chordates also, at some point in their lives, have a nerve cord located towards their backs (dorsally), pharyngeal (gill) slits, and a tail. Yes. We're chordates. You'll have to study developmental biology to learn more about your former tail.


A grouping of organisms on a phylogenetic tree.


Also known as phylogenetic systematics—a way of classifying organisms based on how recently they evolved from their most recent common ancestor. It does not take into account the similarities between organisms' physical/structural characteristics but relies heavily on genetic/molecular information.


A type of phylogenetic tree that shows taxonomic relationships based on organisms' most recent common ancestor. If phylogenetic trees are like family trees, with each new species being another family in the tree, a cladogram is a family tree with a single couple at its base.


A taxon (or group of organisms) made of related orders


The act of placing things into related groups based on their similarities and differences; a grouping.


(Pronounced "see- lum") an inner, fluid-filled space between the digestive tube and the outer wall of an organism. In humans, this space is where our inner organs (for example, kidneys) "float."

Common Ancestor

A species of organisms from which two or more other species have developed or descended, making them all related to each other genetically.

Convergent Evolution

The independent evolution of similar structures in different kinds of organisms.


The set of all possible inputs for which the function is defined.

Domain Archaea

The taxon (group of organisms) containing prokaryotic, unicellular organisms whose cell walls do not contain peptidoglycan (a protein or peptide with a sugar molecule attached). They are all autotrophs. Evolutionarily, this was thought to be the oldest domain; its name means "ancient things." This domain contains just one kingdom of the same name: Kingdom Archaea.

Domain Bacteria

The taxon (group of organisms) containing prokaryotic, unicellular organisms whose cell walls contain peptidoglycan (a protein or peptide with a sugar molecule attached). Most are decomposers; some are parasites that can cause disease; and some are autotrophs. This domain contains just one kingdom of the same name: Kingdom Bacteria.

Domain Eukarya

The taxon (or group of organisms) that includes all eukaryotic organisms. This domain contains the Kingdoms Protista, Fungi, Plantae, and Animalia.


A clade of animals that share a similar pattern of development in which the blastopore becomes the anus of the adult organism. This group contains the Phyla Echinodermata, Hemichordata, and Chordata. Contrast the deuterostomes with the protostomes.


A phylum of deuterostomes within the Kingdom Animalia consisting of marine invertebrates with spiny (Greek: echinos) skin (Greek: dermis) and tube feet. They usually have several identical body parts that surround a central axis (they are radially symmetrical). Examples: sea stars and sea urchins.


An older term for bacteria that you might still find in places. It means "true bacteria" (as opposed to the "weird" bacteria in the Domain Archaea).


Organisms whose cells contain nuclei, which contain their DNA, along with other specialized, membrane-bound organelles

Evolutionary Developmental Biology

"EvoDevo"—the study of how natural selection affects the genes that control animal development. At its heart is the understanding that organisms that are related to each other evolutionarily will share similar patterns of development. No, it's not the name of a new rap artist.


A taxon (group of organisms) made up of related genera.


An early developmental process during which the cells of an embryo move with respect to each other. The embryo begins this stage as a blastula with two types of cells, those on the outside of the ball of cells and those on the inside. Gastrulation involves the some of the outer cells pushing themselves into the ball to form a third layer of cells. (Think about pushing your thumb into an inflated balloon.) Gastrulation forms three germ layers. Watch it happen here.


A group of species that are closely related. The plural of genus is genera.

Germ Layer

One of two to three layers of cells in an early animal embryo that eventually give rise to all of the different tissue types in the adult animal. The formation of germ layers is one of the first developmental processes that create differences in the embryo between one type of cell and another.


An animal phylum of deuterostomes made up of immobile wormlike marine organisms with a three-part body plan and cilia around the mouth. Example: acorn worms (see picture).


An organism that relies on ingesting food and carbon compounds to provide essential energy. We're talking about animals, people, basically anything that has to get its energy by ingesting food. This is opposed to plants, which can whip up their energy straight from the sun.


Ever heard of the "Alpha-male"? Imagine the concept of being the top dog extended to all walks of life. In Huxley's Brave New World, you have Alphas, Betas, Gammas, Deltas, and Epsilons, in that order.


A similarity between two different species that is found by comparing their DNA or amino acid sequences or their structures and processes. The similarity exists because the species are derived from the same common ancestor and are therefore related evolutionarily. Contrast with homoplasy.


A similarity between organisms of different species that is independent of a shared ancestry and is therefore due to convergent evolution, usually thanks to adaptation to similar environments. The two species' most recent common ancestor does not share their similarity. For example, hedgehogs and porcupines both have spiny skin but their common ancestor was a smooth skinned mammal. Contrast with homology.


Animals without bony spines or "vertebrae." Contrast with vertebrates. Kingdom- A large, general taxon (group of organisms) made up of related phyla.

Kingdom Animalia

The eukaryotic taxon (group of organisms) that includes multicellular heterotrophs with complex body plans and diverse lifestyles. Most of them are quite mobile and have a well-coordinated nervous and muscular system, allowing them to react quickly to their environment. They usually reproduce sexually and begin life in an immature form.

Kingdom Archaea

Previously referred to as Kingdom Archaebacteria—the taxon (group of organisms) containing prokaryotic, unicellular organisms whose cell walls do not contain peptidoglycan (a protein or peptide with a sugar molecule attached). This kingdom is the only one in the Domain Archaea.

Kingdom Bacteria

Previously referred to as Kingdom Eubacteria—the taxon (group of organisms) containing prokaryotic, unicellular organisms whose cell walls contain peptidoglycan (a protein or peptide with a sugar molecule attached). Most are decomposers but some are parasites and can cause disease and some are autotrophs. This kingdom is the only one in the Domain Bacteria.

Kingdom Fungi

The taxon (group of organisms) containing eukaryotic heterotrophs that usually get their energy by decomposing dead organic material. They reproduce both asexually and sexually via spores. They can be unicellular or multicellular and their cell walls contain the sugar polymer, chitin. Their most famous member is the mushroom.

Kingdom Plantae

The taxon (group of organisms) that includes non-motile, eukaryotic photoautotrophs. They reproduce sexually, often through seeds. Their most famous member is a tie between the Christmas tree and grass.

Kingdom Protista

The taxon (group of organisms) thought to be the oldest kingdom of eukaryotes (evolutionarily). It includes a wide range of varied organisms, most of which are microscopic. They can be autotrophs or heterotrophs; asexual or sexual; unicellular, multicellular, or colonial. They are all mobile but have different forms of mobility, none of which is walking.

Molecular Systematics

A biological field that uses molecular techniques (such as DNA sequence comparison) to study and compare organisms and their evolutionary relationships.


A point in evolution where a hypothetical ancestor diverged into multiple taxa.


A taxon (group of organisms) made up of related families.


Autotrophs that obtain their energy from sunlight.


Heterotrophs that obtain their energy from sunlight.


Organisms who obtain their energy from the light, such as plants, trees, and glow-in-the-dark t-shirts.

Phylogenetic Tree

A branched, graphical representation of the evolutionary relationships among a group of related species. Think of it as a family tree for non-human organisms.


The evolutionary history of a species or group of species, represented graphically by a phylogenetic tree.


A taxon (group of organisms) made up of related classes.


This is a group of interbreeding individuals of the same species. Technically they don't have to actually interbreed; they just have to be able to at some point in their lives. So even though a grandma elephant isn't making baby elephants anymore, she is still part of the population if she lives in the same area as the rest of the herd.


Unicellular organisms whose DNA is not contained within a nucleus. They also only have a single copy of their genes (they are haploid) and have no organelles.


A member of the Kingdom Protista.


Animals whose mouths develop from the first hole (blastopore) created during the early development of the embryo. Compare them to deuterostomes.


An evolutionary "just kidding!" It happens when a trait reverts back to an earlier form, creating an example of homoplasy.

Shared Ancestral Character

A plesiomorphic character—a trait shared by a current species and an evolutionarily older one that suggests that they share a common ancestor. For example, we call bony vertebrae a shared ancestral character of all vertebrates because all vertebrates came from the same common ancestor, which also had vertebrae.

Shared Derived Character

A synapomorphic character—a trait shared by two or more taxa (groups of organisms) and their most recent common ancestor but not by earlier ancestors, giving us an idea as to when the trait was derived, or developed. For example, amniotic eggs are found in reptiles, birds, and mammals but not other vertebrates like amphibians and fish. This suggests that amniotic eggs are an evolutionary adaptation that was derived by a common ancestor sometime after amphibians and fish evolved.


A group of similar organisms. Members of the same species are able to mate and reproduce. It might be said that Romeo and Juliet should have been two separate species, at least if their parents had anything to do with it.

Species Identifier

A specific epithet—in the binomial system of nomenclature, this is the second word in an organism's name. For example, sapiens is the species identifier for our species Homo sapiens. Think of it as an organism's last name.

Species Name

The two-word name for a species. It is composed of the name of the genus to which the organism belongs followed by the species identifier.


Single cells released by some bacteria and plants and most fungi that can develop into new organisms once the conditions are right. They are an asexual form of reproduction because they do not need to be fertilized to create an adult organism. They are resistant to damage from desiccation (drying out), heat, and many other threats. They allow a population of organisms to be seemingly killed off but to revive again once its spores germinate.


A subset of a species whose members are capable of interbreeding with outside member of the species but usually don't, often because of a geographic barrier.


The study of the diversity of organisms and how they are related evolutionarily. Taxonomy is one part of this field. (Comparative genomics is another, for example.)


(pl. taxa) A category used to classify a group of organisms.


The classification of organisms into different levels of relatedness, such as phylum, family, or species.


A group of cells that function together in some way.


A category of plants that is even more specific than a species. They are genetically distinct but can interbreed. Beefsteak, plum, grape, and cherry tomatoes, for example, are all different varieties of the same species (Solanum lycopersicum). Does Heinz use 57 varieties of tomatoes in their ketchup? We don't know. You'll have to ask them.


Animals with bony spines or "vertebrae." Vertebrates are actually a subphylum of the Phylum Chordata. Fish, amphibians, reptiles, birds, and mammals are all vertebrates. That means you.

Roots of Common Terms in Taxonomy


L = Latin; G = Greek

Auto, Chemo, Hetero, and Phototrophs

trophe = nutrition (G); auto = self, same (G); chemo = chemical (G); heteros = other, different (G); photo = light (G)

Binomial Nomenclature

bis = twice (L), nomen = name (L), calare = to call (L)

Blastula, Blastopore

blastos = sprout (G), pore = hole, opening


klados = branch (G); gram = something written or drawn (G)


eu = true (G); karyon = nucleus (G)


= same, similar (G)


phylon = tribe, race (G); genesis = generation, production (G)


pro = before (G); karyon = nucleus (G)


sub = below (L)


syn = with (G); apo = away from (G); morph = shape, form (G)

Taxon/a, Taxonomy

taxis = arrangement (G); nomie = method (G)


vertebratus = joint of the spine (L)

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