biology-dictionary_11-06-2009

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Aestivation
Cessation from or slowing of activity during the summer; especially slowing of metabolism
in some animals
Afferent
Bringing inward to a central part, applied to nerves and blood vessels.
Agar
A gelatinous material prepared from certain red algae that is used to solidify nutrient media
for growing microorganisms.
Age structure
The relative number of individuals of each age in a population.
Agnathan
A member of a jawless class of vertebrates represented today by the lampreys and
hagfishes.
Agonistic behavior
A type of behavior involving a contest of some kind that determines which competitor gains
access to some resource, such as food or mates.
Alburnum
The outer zone of wood in a tree, next to the bark. Sapwood is generally lighter than
heartwood.
AIDS (acquired immunodeficiency syndrome)
The name of the late stages of HIV infection; defined by a specified reduction of T cells and
the appearance of characteristic secondary infections.
Airsacs
An air-filled space in the body of a bird that forms a connection between the lungs and bone
cavities and aids in breathing and temperature regulation.
Aldehyde
An organic molecule with a carbonyl group located at the end of the carbon skeleton.
Aldosterone
An adrenal hormone that acts on the distal tubules of the kidney to stimulate the
reabsorption of sodium (Na+) and the passive flow of water from the filtrate.

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