Passage 17
Australian researchers have discovered electroreceptors
clustered at the tip of the spiny2 anteaters snout. The
researchers made this discovery by exposing small areas of
the snout to extremely weak electrical fields and recording
the transmission of resulting nervous activity to the brain.
While it is true that tactile3 receptors, another kind of
sensory organ on the anteaters snout, can also respond to
electrical stimuli4, such receptors do so only in response to
electrical field strengths about 1,000 times greater than
those known to excite electroreceptors.
Having discovered the electroreceptors, researchers are
now investigating how anteaters utilize5 such a sophisticated
sensory system. In one behavioral experiment, researchers
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 prey6; however,
researchers as yet have been unable to detect electrical
signals emanating7 from termite8 mounds9, where the favorite
food of anteaters live. Still, researchers have observed
anteaters breaking into a nest of ants at an oblique10 angle
and quickly locating nesting chambers11. This ability quickly
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?
The manner in which electroreceptors respond to electrical stimuli
The tendency of electroreceptors to be found in clusters
The unusual locations in which electroreceptors are found in most species.
The amount of electrical stimulation13 required to excite electroreceptors
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?
Researchers had difficulty verifying the existence of electroreceptors in the anteater because electroreceptors respond to such a narrow range of electrical field strengths.
Researchers found that the level of nervous activity in the anteaters brain increased dramatically as the strength of the electrical stimulus14 was increased.
Researchers found that some areas of the anteaters snout were not sensitive to a weak electrical stimulus.
Researchers found that the anteaters tactile receptors were more easily excited by a strong electrical stimulus than were the electro receptors..
Researchers tested small areas of the anteaters 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 in order to
eliminate and alternative explanation of anteaters response to electrical stimuli
highlight a type of sensory organ that has a function identical to that of electroreceptors
point out a serious complication in the research on electroreceptors in anteaters.
suggest that tactile receptors assist electroreceptors in the detection of electrical signals.
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?
They are unable to distinguish between stimuli detected by their electroreceptors and stimuli detected by their tactile receptors.
They are unable to distinguish between the electrical signals emanating from termite mounds and those emanating from ant nests.
They can be trained to recognize consistently the presence of a particular stimulus.
They react more readily to strong than to weak stimuli.
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?
The event they observed provides conclusive15 evidence that anteaters use their electroreceptors to locate unseen prey.
The event they observed was atypical and may not reflect the usual hunting practices of anteaters.
It is likely that the anteaters located the ants nesting chambers without the assistance of electroreceptors.
Anteaters possess a very simple sensory system for use in locating prey.
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?
Researchers are able to train anteaters to break into an underground chamber12 that is emitting a strong electrical signal.
Researchers are able to detect a weak electrical signal emanating from the nesting chamber of an ant colony.
Anteaters are observed taking increasingly longer amounts of time to locate the nesting chambers of ants.
Anteaters are observed using various angles to break into nests of ants.
Anteaters are observed using the same angle used with nests of ants to break into the nests of other types of prey.
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