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26 Oct 2020, 02:19
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Question 1
E
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
45%
(medium)
Question Stats:
53% (02:38) correct
47%
(02:29) wrong
based on 501
sessions
History
Date
Time
Result
Not Attempted Yet
Question 2
A
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
55%
(hard)
Question Stats:
55% (01:23) correct 45%
(01:45) wrong
based on 443
sessions
History
Date
Time
Result
Not Attempted Yet
Question 3
B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
85%
(hard)
Question Stats:
34% (01:28) correct 66%
(01:26) wrong
based on 436
sessions
History
Date
Time
Result
Not Attempted Yet
In nearly all human populations, a majority of individuals can taste the artificially synthesized chemical phenylthiocarbonide (PTC). However, the percentage varies dramatically—from as low as 60 percent in India to as high as 95 percent in Africa. That this polymorphism is observed in nonhuman primates as well indicates a long evolutionary history which, although obviously not acting on PTC, might reflect evolutionary selection for taste discrimination of other, more significant, bitter substances, such as certain toxic plants.
A somewhat more puzzling human polymorphism is the genetic variability in earwax, or cerumen, which is observed in two varieties. Among European populations, 90 percent of individuals have a sticky yellow variety rather than a dry, gray one, whereas in northern China these numbers are approximately the reverse. Perhaps like PTC variability, cerumen variability is an incidental expression of something more adaptively significant. Indeed, the observed relationship between cerumen and odorous bodily secretions, to which nonhuman primates—and to a lesser extent humans—pay attention suggests that during the course of human evolution genes affecting body secretions, including cerumen, came under selective influence.
A somewhat more puzzling human polymorphism is the genetic variability in earwax, or cerumen, which is observed in two varieties. Among European populations, 90 percent of individuals have a sticky yellow variety rather than a dry, gray one, whereas in northern China these numbers are approximately the reverse. Perhaps like PTC variability, cerumen variability is an incidental expression of something more adaptively significant. Indeed, the observed relationship between cerumen and odorous bodily secretions, to which nonhuman primates—and to a lesser extent humans—pay attention suggests that during the course of human evolution genes affecting body secretions, including cerumen, came under selective influence.
1. It can be inferred from the passage that human populations vary considerably in their
(A) sensitivity to certain bodily odors.
(B) capacity for hearing.
(C) ability to assimilate artificial chemicals.
(D) vulnerability to certain toxins found in plants.
(E) ability to discern bitterness in taste.
(A) sensitivity to certain bodily odors.
(B) capacity for hearing.
(C) ability to assimilate artificial chemicals.
(D) vulnerability to certain toxins found in plants.
(E) ability to discern bitterness in taste.
2. Which of the following provides the most reasonable explanation for the assertion in the first paragraph that evolutionary history “obviously” did not act on PTC?
(A) PTC is not a naturally occurring chemical but rather has been produced only recently by scientists.
(B) Most humans lack sufficient taste sensitivity to discriminate between PTC and bitter chemicals occurring naturally.
(C) Variability among humans respecting PTC discrimination, like variability respecting earwax, cannot be explained in terms of evolutionary adaptivity.
(D) The sense of taste in humans is not as discriminating as that in nonhuman primates.
(E) Unlike nonhuman primates, humans can discriminate intellectually between toxic and nontoxic bitter substances.
(A) PTC is not a naturally occurring chemical but rather has been produced only recently by scientists.
(B) Most humans lack sufficient taste sensitivity to discriminate between PTC and bitter chemicals occurring naturally.
(C) Variability among humans respecting PTC discrimination, like variability respecting earwax, cannot be explained in terms of evolutionary adaptivity.
(D) The sense of taste in humans is not as discriminating as that in nonhuman primates.
(E) Unlike nonhuman primates, humans can discriminate intellectually between toxic and nontoxic bitter substances.
3. Which of the following best expresses the main idea of the passage?
(A) Artificially synthesized chemicals might eventually serve to alter the course of evolution by desensitizing humans to certain tastes and odors.
(B) Some human polymorphisms might be explained as vestigial evidence of evolutionary adaptations that still serve vital purposes in other primates.
(C) Sensitivity to taste and to odors have been subject to far greater natural selectivity during the evolution of primates than previously thought.
(D) Polymorphism among human populations varies considerably from region to region throughout the world.
(E) The human senses of taste and smell have evolved considerably over the course of evolutionary history.
(A) Artificially synthesized chemicals might eventually serve to alter the course of evolution by desensitizing humans to certain tastes and odors.
(B) Some human polymorphisms might be explained as vestigial evidence of evolutionary adaptations that still serve vital purposes in other primates.
(C) Sensitivity to taste and to odors have been subject to far greater natural selectivity during the evolution of primates than previously thought.
(D) Polymorphism among human populations varies considerably from region to region throughout the world.
(E) The human senses of taste and smell have evolved considerably over the course of evolutionary history.
29 Oct 2020, 03:32
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Official Explanation
3. Which of the following best expresses the main idea of the passage?
Explanation
In the first paragraph, the author’s main concern is to point out that the variability among human populations regarding sensitivity to PTC might be a trace of the evolutionary process of natural selectivity.
In the second paragraph, the author offers a similar suggestion about variability in earwax type. To support these assertions, the author implies that both characteristics still serve useful purposes among non primates—from whom humans presumably evolved.
This inference is especially clear with respect to identifying bitter substances that might be toxic. Choice (B) accurately reflects the author’s main assertion and supporting evidence.
The correct answer is (B).
Explanation
In the first paragraph, the author’s main concern is to point out that the variability among human populations regarding sensitivity to PTC might be a trace of the evolutionary process of natural selectivity.
In the second paragraph, the author offers a similar suggestion about variability in earwax type. To support these assertions, the author implies that both characteristics still serve useful purposes among non primates—from whom humans presumably evolved.
This inference is especially clear with respect to identifying bitter substances that might be toxic. Choice (B) accurately reflects the author’s main assertion and supporting evidence.
The correct answer is (B).
05 Sep 2021, 12:49
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Official Explanation
1. It can be inferred from the passage that human populations vary considerably in their
Explanation
In the passage’s first paragraph, the author points out that the ability to taste PTC varies among human populations. Then, in the final sentence of that paragraph, the author refers to “other, more significant, bitter substances. . . .” It can reasonably be inferred from these two statements, considered together, that PTC is a bitter substance.
The correct answer is (E).
Explanation
In the passage’s first paragraph, the author points out that the ability to taste PTC varies among human populations. Then, in the final sentence of that paragraph, the author refers to “other, more significant, bitter substances. . . .” It can reasonably be inferred from these two statements, considered together, that PTC is a bitter substance.
The correct answer is (E).
