Science / Biology Glossary

Coronary Arteries: Arteries that supply the hearts muscle fibers with nutrients and oxygen.

Corpus Callosum: Tightly bundled nerve fibers that connect the right and left hemispheres of the cerebrum.

Corpus Luteum: A structure formed from the ovulated follicle in the ovary; secretes progesterone and estrogen.

Cortex: 1) The outer part of an organ, e.g., the adrenal cortex, which produces several steroid hormones; 2) in plants, the region of the stem or root between the epidermis and the vascular bundle(s).

Cortisol: The primary glucocorticoid hormone; released by the adrenal cortex.

Cotyledon: A leaf-like structure that is present in the seeds of flowering plants; appears during seed germination and sometimes is referred to as a seed leaf.

Countercurrent Flow: An arrangement by which fish obtain oxygen from the water that flows through their gills. Water flows across the respiratory surface of the gill in one direction while blood flows in the oth . . . View Full Definition

Courtship Behavior: Behavioral sequences that precede mating.

Covalent Bond: A chemical bond created by the sharing of electrons between atoms.

Cranium: The braincase; composed of several bones fitted together at immovable joints.

Cretaceous Period: The geologic period between the Jurassic Period (140 milliojn years ago) and the Tertiary Period (beginning 65 million years ago). The Cretaceous was marked by a mass extinction that closed . . . View Full Definition

Cristae: Structures formed by the folding of the inner membrane of a mitochondrion (sing.: crista).

Crossing-Over: During the first meiotic prophase, the process in which part of a chromatid is physically exchanged with another chromatid to form chromosomes with new allele combinations.

Crossopterygians: A type of lobe-finned fish with lungs that were ancestral to amphibians.

Crustaceans: A large taxonomic class of arthropods that includes lobsters, shrimps, and crabs.

Cuticle: A film composed of wax and cutin that occurs on the external surface of plant stems and leaves and helps to prevent water loss.

Cyanobacteria: Blue-green bacteria; unicellular or filamentous chains of cells that carry out photosynthesis.

Cycadeoids: A group of gymnosperm seed plants not closely rated to, but superficially similar to, the cycads. Cycads and cycadeoids were dominant floristic elements of early and middle Mesozoic landscap . . . View Full Definition

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