What happens when the membrane potential of a neuron reaches the threshold level?
a. Voltage-gated sodium channels open, and sodium diffuses out of the cell.
b. Voltage-gated potassium channels open for a very brief period.
c. Voltage-gated sodium channels close, so sodium cannot diffuse out of the cell.
d. The sodium channel protein changes its shape to open the gates of the channel.
e. The membrane potential is more negative than when at rest.
d
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When arginine is added to a culture growing exponentially in a medium without arginine, what occurs?
A) All cellular growth ceases. B) Growth continues, but the production of enzymes required for the synthesis of arginine ceases. C) Growth continues, but the production of enzymes required for the synthesis of arginine increases. D) The cell returns to the lag stage of growth to synthesize the proteins necessary for the metabolism of arginine.
Which of the following is mismatched?
a. cytokinin – inhibits lateral root formation b. auxin – promotes cell elongation
c. gibberellin – involved in phototropism and gravitropism d. abscisic acid – promotes stomatal closure e. ethylene – promotes leaf abscission
Figure 40.7
The region where filtration occurs is indicated by the letter(s) ____.
A. A B. B C. C D. D E. A and D
Characters such as height, weight, and skin color are controlled by many genes acting together. These are examples of:
A) multiple alleles. B) codominance. C) polygenic inheritance. D) incomplete dominance.