Glossary of Terms
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
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- A -
- adaptive
radiation
- the relatively rapid expansion and diversification of an evolving group of organisms as they adapt to new ecological niches. Adaptive radiation is the process by which one species evolves into two or more species. This occurs as a result of different populations becoming reproductively isolated from each other, usually by adapting to different environments.
- amino acids
- organic molecules that are building blocks of proteins. There are at least 20 different kinds of amino acids in living things. Proteins are composed of different combinations of amino acids assembled in chain-like molecules. Amino acids are primarily composed of carbon, oxygen, hydrogen, and nitrogen.
- amniote
- referring to an egg with a hard shell and protective membranes that prevent the embryo from rapidly drying out. Reptiles, birds, and prototherian mammals lay amniote eggs.
- Amphibia
- the class of vertebrates that includes frogs, toads, and salamanders. Amphibians spend part of their lives under water and part on land. They must return to damp areas to reproduce since their eggs would otherwise dry out. They start life with gills, like fish, and later develop lungs to breath air.
- anaerobic
- without oxygen
- analogies
- anatomical features that have the same form or function in different species that have no known common ancestor. Analogies are also referred to as analogous structures or features.
- analogous structures
- see analogies.
- Animalia
- the kingdom of living things that includes all animals. They are multicellular organisms that ingest food rather than absorb or photosynthesize it. They also have their own means of locomotion in at least one phase of their life cycles.
- anterior
- see dorsal.
- Arthropoda
- the animal phylum consisting of creatures that have external skeletons, and jointed bodies and limbs. Insects, spiders, lobsters, and crabs are arthropods.
- Aves
- the class of vertebrates that includes all of the birds. Like reptiles, they lay amniote eggs.
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- B -
- bilaterally
symmetrical
- the chordate characteristic of the left and right sides of the body being mirror images of each other. If there are two functionally similar body parts, they are usually found roughly equidistant from the center line, parallel to each other on bilaterally symmetrical animals.
- binomen
- the Linnaean classification system use of two Latin name categories, genus and species, to designate each type of organism. A genus is a higher level category that includes one or more species under it. For example, humans are Homo sapiens, or "man who is wise"--Homo is our genus and sapiens is our species. Binomen literally means "two names" in Latin. Binomial nomenclature is another term for binomen.
