The convergence in external morphology of sharks,
penguins, and porpoises is attributed to
a. reduced genetic variability in these groups.
b. selection pressures that are common to these
groups.
c. reproductive isolation of these groups.
d. identical genes in all three groups.
e. use and disuse of the limbs.
Answer: b
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Which of the following is not true of the ? helix?
A. The ? helix forms a right-handed spiral. B. Amino acid R groups point toward the helical axis. C. The hydrogen bonds of an ? helix all point in the same direction. D. A typical protein contains about one-third ? helix. E. All of the answers given are correct.
The outside of a neuron is positively charged at resting potential. Why don't negative ions exit from the cell to normalize charge across the membrane?
A. The positive charge outside the cell repels negative ions. B. There are no negative ions inside the cell. C. All of the chloride ions are already outside the cell. D. The negative charge inside the cell is carried by large proteins that cannot diffuse through the membrane.
Supercomplexes of electron transport complexes are known as
A) Q complexes. B) chemiosmotic coupling complexes. C) Fe-S centers. D) respirasomes. E) NADH dehydrogenase complexes.
Which of the following sections of the mammalian nephron is incorrectly paired with its function?
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