Science / Biology Glossary

Channels: Transport proteins that act as gates to control the movement of sodium and potassium ions across the plasma membrane of a nerve cell.

Chemical Equilibrium: The condition when the forward and reverse reaction rates are equal and the concentrations of the products remain constant.

Chemiosmosis: The process by which ATP is produced in the inner membrane of a mitochondrion. The electron transport system transfers protons from the inner compartment to the outer; as the protons flow ba . . . View Full Definition

Chemotrophs: Organisms (usually bacteria) that derive energy from inorganic reactions; also known as chemosynthetic.

Chiasma: The site where the exchange of chromosome segments between homologous chromosomes takes place (crossing-over) (pl.: chiasmata).

Chitin: A polysaccharide contained in fungi; also forms part of the hard outer covering of insects.

Chlamydia: A sexually transmitted disease caused by a parasitic bacterium that lives inside cells of the reproductive tract.

Chlorofluorocarbons (CFCS): Chemical substances used in refrigerators, air conditioners, and solvents that drift to the upper stratosphere and dissociate. Chlorine released by CFCs reacts with ozone, eroding the ozone layer.

Chlorophyll: The pigment in green plants that absorbs solar energy.

Chlorophyll A: The green photosynthetic pigment common to all photosynthetic organisms.

Chlorophyll B: An accessory chlorophyll found in green algae and plants.

Chlorophyll C: An accessory chlorophyll found in some protistans.

Chlorophyta: The taxonomic division that contains what are commonly called the green algae.

Chloroplasts: Disk-like organelles with a double membrane found in eukaryotic plant cells; contain thylakoids and are the site of photosynthesis. ATP is generated during photosynthesis by chemiosmosis.

Cholecystokinin: A hormone secreted in the duodenum that causes the gallbladder to release bile and the pancreas to secrete lipase.

Chorion: The two-layered structure formed from the trophoblast after implantation; secretes human chorionic gonadotropin.

Chorionic Villi Sampling (CVS): A method of prenatal testing in which fetal cells from the fetal side of the placenta (chorionic villi) are extracted and analyzed for chromosomal and biochemical defects.

Chromatid: Generally refers to a strand of a replicated chromosome; consists of DNA and protein.

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