Casparian strip
A water-impermeable ring of wax around endodermal cells in plants that blocks the passive
flow of water and solutes into the stele by way of cell walls.
Catabolic pathway
A metabolic pathway that releases energy by breaking down complex molecules into
simpler compounds.
Catabolism
Within a cell or organism, the sum of all chemical reactions in which large molecules are
broken down into smaller parts.
Catabolite activator protein (CAP)
In E. coli, a helper protein that stimulates gene expression by binding within the promoter
region of an operon and enhancing the promoter's ability to associate with RNA polymerase.
Catalyst
A substance that lowers the activation energy of a chemical reaction by forming a
temporary association with the reacting molecules; as a result, the rate of the reaction is
accelerated. Enzymes are catalysts.
Category
In a hierarchical classification system, the level at which a particular group is ranked.
Cation
An ion with a positive charge, produced by the loss of one or more electrons.
Cation exchange
A process in which positively charged minerals are made available to a plant when hydrogen
ions in the soil displace mineral ions from the clay particles.
Cdc genes
A gene that regulates the cell cycle. Also known as CDC gene.
Cell
A basic unit of living matter separated from its environment by a plasma membrane; the
fundamental structural unit of life.
Cell center
A region in the cytoplasm near the nucleus from which microtubules originate and radiate.
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