The phospholipid molecules of most membranes have
a. a hydrophobic head and a hydrophilic tail.
b. a hydrophobic head and a hydrophobic tail.
c. a hydrophobic head and two hydrophobic tails.
d. a hydrophilic head and two hydrophobic tails.
e. two hydrophobic tails.
D
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Land ecosystems lose nitrogen to aquatic systems through ____
a. decomposition b. ammonification c. soil leaching d. bacterial fixation e. denitrification
The Calvin cycle depends on a supply of both ___________ and NADPH from the light reactions.
Fill in the blank(s) with the appropriate word(s).
Concerning fermentation, pyruvate is to lactic acid in muscle cells as __________ is to __________ in yeast.
a. lactic acid; water b. pyruvate; oxygen c. sugars; proteins d. ATP; NADH e. acetaldehyde; ethanol
Which principle of heat exchange is the most important explanation for why birds look larger in colder weather because they fluff their feathers?
A) Fluffing feathers results in less cooling by radiation because feathers emit less infrared radiation than other tissues do. B) Fluffing decreases the amount of heat lost by conduction when the bird makes contact with cold objects in its environment. C) Fluffing creates a pocket of air near the bird that acts as insulation. D) Fluffing decreases the surface-area-to-volume ratio, thus decreasing the amount of heat lost to the environment.