Tunicates
Any of various sedentary tunicates of the class Ascidiacea, having a transparent sac-shaped
body with two siphons. Also called ascidian.
Turgid
Firm; walled cells become turgid as a result of the entry of water from a hypotonic
environment.
Turgor
Pressure exerted by fluid in a cell that presses the cell membrane against the cell wall.
Turgor pressure
The force directed against a cell wall after the influx of water and the swelling of a walled
cell due to osmosis.
Twisted
To interlock or interlace.
Tympanic
Relating to the middle ear or eardrum.
Tympanum
The main cavity of the ear, between the eardrum and the inner ear.
Tyrosine kinase
An enzyme that catalyzes the transfer of phosphate groups from ATP to the amino acid
tyrosine in a substrate protein.
Tyrosine kinase receptor
A receptor protein in the plasma membrane that responds to the binding of a signal
molecule by catalyzing the transfer of phosphate groups from ATP to tyrosines on the
cytoplasmic side of the receptor. The phosphorylated tyrosines activate other signal-
transduction proteins within the cell.
U
Ultimate causation
The hypothetical evolutionary explanation for the existence of a certain pattern of animal
behavior.