Sat practice Test #8 Answer Explanations

Choice D is the best answer. The third paragraph explains that 
touching a single trigger hair results in “a rapid increase in the 
concentration of calcium ions” in the plant. The fourth paragraph 
further explains that the calcium concentration produced by this initial 
touch isn’t enough to cause the trap to close, but that a second hair 
touch will bring the total concentration to the level necessary to close 
the trap: “a second hair needs to be stimulated to push the calcium 
concentration over this threshold and spring the trap.”
Choices A and B are incorrect because the fourth paragraph explains 
that the second trigger supplements the action of the first trigger, not 
that it reverses it (choice A) or stabilizes its effect (choice B). Choice C 
is incorrect because the third paragraph clearly states that the calcium 
channels open after the first trigger hair is touched, not the second.
QUESTION 48
Choice B is the best answer. The fourth paragraph explains that 
the Venus flytrap will close only if a second hair is stimulated to 
“push the calcium concentration over this threshold and spring the 
trap.” But the last sentence of the paragraph notes that the calcium 
concentrations “dissipate over time,” and if enough time elapses after 
the first trigger, “the final concentration after the second trigger won’t 
be high enough to close the trap.” It can be inferred, then, that if a 
large insect didn’t touch a second trigger hair until after the calcium 
ion concentrations had diminished appreciably, the Venus flytrap 
would fail to close.

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Choice A is incorrect because the fourth paragraph makes clear that 
if the calcium concentration goes above the trap’s threshold, the plant 
will close, not remain open. Choice C is incorrect because as the third 
paragraph explains, the touching of the trigger hair and opening of the 
calcium ion channels don’t act to keep the trap open but are instead 
a precondition for the closing of the trap (though closing will occur 
only if a second trigger hair is touched). Choice D is incorrect because 
the last sentence of the fifth paragraph explains that the threshold 
for the time that can elapse between the touching of the first and 
second trigger hairs is twenty seconds, meaning that a large insect 
touching two hairs within ten seconds would almost certainly make the 
plant close.
QUESTION 49