C 4 pathway
The set of reactions by which some plants initially fix carbon in the four-carbon compound
oxaloacetic acid; the carbon dioxide is later released in the interior of the leaf and enters the
Calvin cycle.
C 4 plant
A plant that prefaces the Calvin cycle with reactions that incorporate CO 2 into four-carbon
compounds, the end-product of which supplies CO 2 for the Calvin cycle.
Cartilage
A tough, elastic, fibrous connective tissue found in various parts of the body, such as the
joints, outer ear, and larynx. A major constituent of the embryonic and young vertebrate
skeleton, it is converted largely to bone with maturation.
Caretenoids
Any of a group of yellow, orange, red, or brown pigments found in many living organisms,
particularly in the chloroplasts of plants.
Calcaneum
The quadrangular bone at the back of the tarsus. Also called heel bone.
Calcitonin
A mammalian thyroid hormone that lowers blood calcium levels.
Calcium oxalate
A small, colorless crystal that may be present in urine or may be a component of real calculi.
Callus
In plants, undifferentiated tissue; a term used in tissue culture, grafting, and wound healing.
Calmodulin
An intracellular protein to which calcium binds in its function as a second messenger in
hormone action.
Calorie
The amount of heat energy required to raise the temperature of 1 g of water 1°C; the
amount of heat energy that 1 g of water releases when it cools by 1°C. The Calorie (with a
capital C), usually used to indicate the energy content of food, is a kilocalorie.
Calvin cycle
The second of two major stages in photosynthesis (following the light reactions), involving
atmospheric CO 2 fixation and reduction of the fixed carbon into carbohydrate.
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