biology-dictionary_11-06-2009

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Coupled reactions
In cells, the linking of endergonic (energy-requiring) reactions to exergonic (energy-
releasing) reactions that provide enough energy to drive the endergonic reactions forward.
Covalent bond
A chemical bond formed as a result of the sharing of one or more pairs of electrons.
Crassulacean acid metabolism
A process by which some species of plants in hot, dry climates take in carbon dioxide during
the night, fixing it in organic acids; the carbon dioxide is released during the day and used
immediately in the Calvin cycle.
Cranial
Relating to the skull or cranium.
Cretaceous
Belonging to the geologic time, system of rocks, and sedimentary deposits of the third and
last period of the Mesozoic Era, characterized by the development of flowering plants and
ending with the sudden extinction of the dinosaurs and many other forms of life.
Crista
An infolding of the inner membrane of a mitochondrion that houses the electron transport
chain and the enzyme catalyzing the synthesis of ATP.
Crop
Cultivated plants or agricultural produce, such as grain, vegetables, or fruit, considered as a
group: Wheat is a common crop.
Cross-fertilization
Fusion of gametes formed by different individuals; as opposed to self-fertilization.
Crossing over
The reciprocal exchange of genetic material between nonsister chromatids during synapsis
of meiosis I.
Cryptic coloration
A type of camouflage that makes potential prey difficult to spot against its background.
Ctenidia
A comblike respiratory structure serving as the gill of certain mollusks.
Ctenoid
Having marginal projections that resemble the teeth of a comb: a ctenoid fish.

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