Australian researchers have discovered electroreceptors (sensory organs designed to respond to electrical fields) clustered at the tip of the spiny anteater’s snout. The researchers made this discovery by exposing small areas of
(5) the snout to extremely weak electrical fields and recording the transmission of resulting nervous activity to the brain. While it is true that tactile receptors, another kind of sensory organ on the anteater’s snout, can also respond to electrical stimuli, such receptors do so only in response to
( 10) electrical field strengths about 1,000 times greater than those known to excite electroreceptors.
Having discovered the electroreceptors, researchers are now investigating how anteaters utilize such a sophisticated sensory system. In one behavioral experiment, researchers
(15) successfully trained an anteater to distinguish between two troughs of water, one with a weak electrical field
and the other with none. Such evidence is consistent with researchers’ hypothesis that anteaters use electroreceptors to detect electrical signals given off by prey; however,
( 20)researchers as yet have been unable to detect electrical signals emanating from termite mounds, where the favorite food of anteaters live. Still, researchers have observed anteaters breaking into a nest of ants at an oblique angle and quickly locating nesting chambers. This ability quickly
(25)to locate unseen prey suggests, according to the researchers, that the anteaters were using their electroreceptors to locate the nesting chambers.
101.According to the passage, which of the following is a
characteristic that distinguishes electroreceptors from tactile receptors?
(A)The manner in which electroreceptors respond to electrical stimuli
(B)The tendency of electroreceptors to be found in clusters
(C)The unusual locations in which electroreceptors are found in most species.
(D)The amount of electrical stimulation required to excite electroreceptors
(E)The amount of nervous activity transmitted to the brain by electroreceptors when they are excited
102.Which of the following can be inferred about the experiment described in the first paragraph?
(A)Researchers had difficulty verifying the existence of electroreceptors in the anteater because electroreceptors respond to such a narrow range of electrical field strengths.
(B)Researchers found that the level of nervous activity in the anteater’s brain increased dramatically as the strength of the electrical stimulus was increased.
(C)Researchers found that some areas of the anteater’s snout were not sensitive to a weak electrical stimulus.
(D)Researchers found that the anteater’s tactile receptors were more easily excited by a strong electrical stimulus than were the electro receptors..
(E)Researchers tested small areas of the anteater’s snout in order to ensure that only electroreceptors were responding to the stimulus.
103.The author of the passage most probably discusses the function of tactile receptors (lines 7-11) in order to
(A)eliminate and alternative explanation of anteaters’ response to electrical stimuli
(B)highlight a type of sensory organ that has a function identical to that of electroreceptors
(C)point out a serious complication in the research on electroreceptors in anteaters.
(D)suggest that tactile receptors assist electroreceptors in the detection of electrical signals.
(E)introduce a factor that was not addressed in the
research on electroreceptors in anteaters.
10 4. Which of the following can be inferred about anteaters from the behavioral experiment mentioned in the second paragraph?
(A)They are unable to distinguish between stimuli detected by their electroreceptors and stimuli detected by their tactile receptors.
(B)They are unable to distinguish between the electrical signals emanating from termite mounds and those emanating from ant nests.
(C)They can be trained to recognize consistently the presence of a particular stimulus.
(D)They react more readily to strong than to weak stimuli.
(E)They are more efficient at detecting stimuli in a controlled environment than in a natural environment.
105.The passage suggests that the researchers mentioned in the second paragraph who observed anteaters break into a nest of ants would most likely agree with which of the following statements?
(A)The event they observed provides conclusive evidence that anteaters use their electroreceptors to locate unseen prey.
(B)The event they observed was atypical and may not reflect the usual hunting practices of anteaters.
(C)It is likely that the anteaters located the ants’ nesting chambers without the assistance of electroreceptors.
(D)Anteaters possess a very simple sensory system for use in locating prey.
(E)The speed with which the anteaters located their prey is greater than what might be expected on the basis of chance alone.
106.Which of the following, if true, would most strengthen the hypothesis mentioned in lines 17-19?
(A)Researchers are able to train anteaters to break into an underground chamber that is emitting a strong electrical signal.
(B)Researchers are able to detect a weak electrical signal emanating from the nesting chamber of an ant colony.
(C)Anteaters are observed taking increasingly longer amounts of time to locate the nesting chambers of ants.
(D)Anteaters are observed using various angles to break into nests of ants.
(E)Anteaters are observed using the same angle used with nests of ants to break into the nests of other types of prey.
The best answer is D. According to the passage, the electrorecepors in the snouts of spiny anteaters responds to extremely weak electrical fields. In lines 7-11, the author of the passage contrasts these electroreceptors with tactile receptors, stating that it takes field strengths “about 1,000 times greater than those known to excite electroreceptors” to excite the tactile receptors on an anteater’s snout. The passage does not contrast the two types of receptors with regard to the characteristics mentioned in choices A, B, C, and E.
The best answer is C. In the experiment described in the first passage, researchers described the electroreceptors in the anteater’s snout as “clustered” at the tip. Thus, it can be inferred that nervous activity was not recorded across the entire snout, but only in certain areas. Therefore, some areas of the snout, including those containing the tactile receptors, were not stimulated by the weak fields used in the experiment, as choice C suggests. There is no information in the description of the experiment provided in the passage to suggest A, B, D, or E.
The best answer is A. Because tactile receptors also respond to electrical stimulation, the researchers’ conclusion that electroreceptors exist is valid only if it can be demonstrated that the nervous activity recorded in the anteater’s brain did not originate in the tactile receptors. There is no indication in the passage that tactile receptors function like electroreceptors (B) or that tactile receptors assist electroreceptors (D). There is no information in the passage to suggest that the presence of tactile receptors complicated research on electroreceptors, so C is not correct. Choice E is not correct because the information in lines 7-11 is presented in addition to information about the experiment and not as a criticism or to point out an omission.
The best answer is C. Lines 14-17 state that anteaters were “successfully trained” by researchers “to distinguish between two troughs of water,” only one of which had an electrical field. Choices A, B, D, and E can be eliminated because they present hypotheses about anteater behavior that were not tested in the experiment and are not discussed in the passage.
The best answer is E. The last sentence in the passage implies that the researchers believed that the anteaters’ locating of their unseen prey was too prompt and too deliberate to be accidental. Choice A is incorrect: researchers were unable to confirm that the anteaters’ favorite prey, termites, emitted electrical signals, and the observation of anteaters locating ants’ nesting chambers “suggests” (lines 25), rather than proves conclusively, that anteaters use their electroreceptors to find prey. Choice B is incorrect because here is no indication in the passage that researchers believed that the anteaters’ behavior was atypical. Choice E is incorrect because, according to lines 24-27, the researchers believed that the anteaters “were using their electroreceptors to locate the nesting chambers”. Choice D is contradicted by the passage: in line 13, the anteater’s sensory system is described as “sophisticated”.
The best answer is B. The researchers’ hypothesis is “that anteaters use electroreceptors to detect electrical signals given off by prey.” Evidence that electrical signals emanate from the nesting
chamber of an ant colony-on which anteaters are known to prey-would strengthen the hypothesis. Choice C may actually weaken the hypothesis: the passage implies that the rapidity with which anteaters were able to locate ants’ nesting chambers suggested to researchers that anteaters were using electroreceptors to locate prey. Choice A, D, and E provide evidence that does not strengthen the hypothesis.