Tropical rain forest
The most complex of all communities, located near the equator where rainfall is abundant;
harbors more species of plants and animals than all other terrestrial biomes combined.
Tropism
A growth response that results in the curvature of whole plant organs toward or away from
stimuli due to differential rates of cell elongation.
Truncus arteriosus
An artery connected with the fetal heart, developing into the aortic and pulmonary arches.
The trunk may persist into extrauterine life. The single arterial trunk from the heart supplies
blood to both aortic and pulmonary circuits.
Tuatara
Either of two nocturnal lizardlike reptiles (Sphenodon punctatus or S. guntheri) that are
found only on certain islands off New Zealand and are the only extant members of the
Rhynchocephalia, an order that flourished during the Mesozoic Era. Also called sphenodon.
Tuber
A much-enlarged, short, fleshy underground stem, such as that of the potato.
Tuberous stem
Producing or bearing tubers.
Tubulin
The constituent protein of microtubules of cells which provide a skeleton for maintaining
cell shape and is thought to be involved in cell motility.
Tumor
A mass that forms within otherwise normal tissue, caused by the uncontrolled growth of a
transformed cell.
Tumor suppressor gene
A gene whose protein products inhibit cell division, thereby preventing uncontrolled cell
growth (cancer).
Tundra
A biome at the extreme limits of plant growth; at the northernmost limits, it is called arctic
tundra, and at high altitudes, where plant forms are limited to low shrubby or matlike
vegetation, it is called alpine tundra.
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