C Biological TERMS 
Calvin cycle The set of steps in photosynthesis through which carbon dioxide, with energy from ATP and electrons from NADPH, becomes an energetic carbohydrate. This cycle is the stage of photosynthesis where building occurs.
CAM metabolism A type of photosynthesis used by succulents and some other plants from dry climates. In it, stomata stay open at night, allowing CO2 to enter the plant, but then close during the day, thereby conserving water. Carbon thus "banked" during the night is used the following day in the plant's completion of photosynthesis.
capillary The smallest type of blood vessel, connecting the arteries and veins out in the body's tissues. Gases, nutrients, and wastes are exchanged between the blood and the tissues through the thin walls of capillaries.
capillary bed An interconnected network of capillaries that lies in the body's tissues. The network brings the capillaries close to each part of the tissues and provides lots of surface area for more efficient diffusion.
carbohydrate A class of biological molecule that contains carbon, oxygen, and hydrogen, usually with twice as much hydrogen as oxygen. Carbohydrates are composed of monosaccharide (simple sugar) building blocks. Starch, cellulose, and glycogen, and are carbohydrates.
carcinogen Any environmental influence that can contribute to the onset of cancer.
cardiac muscle The type of striated muscle tissue that forms the muscles of the heart.
cardiovascular system The organ system that transports nutrients, dissolved gases, and hormones to tissues throughout the body, and carries wastes to sites of filtration. This system consists of the heart, blood vessels, and blood, and the bone marrow where blood cells are formed.
carnivore An animal that eats meat.
carpel The female reproductive structure of a flower, consisting of an ovary, a style, and a stigma.
carrier A person who does not suffer from a recessive genetic debilitation, but who carries genes for it that can be passed along to offspring.
carrying capacity The maximum population of a species that can be sustained in a given geographical area over time. In ecology, this is often denoted as K.
cartilage A type of supportive connective tissue that provides support and flexibility, as in the outer portions of the nose and ear, between bones of the spine, and between limb bones.
catalyst A substance that retains its original chemical composition while bringing about a change in a substrate. Enzymes are catalysts in chemical reactions, and one enzyme can carry out hundreds or thousands of chemical transformations.
cecum An expanded chamber at the beginning of the large intestine, adjacent to the small intestine. In some animals, especially herbivores, the cecum is a fermentation chamber for gut microorganisms that digest cellulose.
cell A highly organized structure that consists of a cell membrane with cytoplasm (cell fluid) and DNA inside. A cell can be an entire organism on its own or can be a building block for tissues and other structures in a multi-celled organism like a human. Cells are the structural units of all organisms.
cell cycle The repeating pattern of growth, genetic duplication, and division that many types of cells undergo. The cell cycle has two main phases: interphase, in which cells grow, duplicate chromosomes, and work, and mitotic phase, in which cells divide.
cell junction A linkage between animal cells. A gap junction is a type of cell junction that facilitates cell communication.
cell-mediated immunity An immune system capability that works through the production of cells that destroy infected cells in the body..
cell plate A membranous sac that, in cell division, is the precursor to the plant cell wall.
cell wall A structure composed mostly of cellulose and lignin that surrounds the plasma membrane in plants. The cell wall provides structure and helps regulate water intake.
cellular respiration The process of extracting energy from a food molecule such as glucose to form ATP, the most useful form of energy in a cell. Three stages are included: glycolysis, Krebs cycle, and the electron transport chain.
