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Medical College Admission Test: Verbal Reasoning, Biological Sciences, Physical Sciences, Writing Sample (Page 23 )

Updated On: 25-Apr-2026
Page 23 of 164
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One of the basic principles of ecology is that population size is to some extent a function of available food resources. Recent field experiments demonstrate that the interrelationship may be far more complex than hitherto imagined. Specifically, the browsing of certain rodents appears to trigger biochemical reactions in the plants they feed on that help regulate the size of the rodent populations. Two such examples of phytochemical regulation (regulation involving plant chemistry) have been reported so far.
Patricia Berger and her colleagues at the University of Utah have demonstrated that instrumentality of 6- methoxybenzoxazolinone (6-MBOA) in triggering reproductive behavior in the mountain vole (Microtus montanus), a small rodent resembling the field mouse. 6-MBOA forms in young mountain grasses in response to browsing by predators such as voles. The experimenters fed rolled oats coated with 6-MBOA to non- breeding winter populations of Microtus. After three weeks, the sample populations revealed a high incidence of pregnancy among the females and pronounced swelling of the testicles among the males. Control populations receiving no 6- MBOA revealed no such signs. Since the timing of reproductive effort is crucial to the short-lived vole in an environment in which the onset of vegetative growth can vary by as much as two months, the phytochemical triggering of copulatory behavior in Microtus represents a significant biological adaptation.
A distinct example is reported by John Bryant of the University of Alaska. In this case, plants seem to have adopted a form of phytochemical self-defense against the depredations of the snowshoe hare (Lepus americanus) of Canada and Alaska. Every ten years or so, for reasons that are not entirely understood, the Lepus population swells dramatically. The result is intense overbrowsing of early and mid-successional deciduous trees and shrubs. Bryant has shown that, as if in response, four common boreal forest trees favored by Lepus produce adventitious shoots high in terpene and phenolic resins which effectively discourage hare browsing. He treated mature, non-resinous willow twigs with resinous extracts from the adventitious shoots of other plants and placed treated and untreated bundles at hare feeding stations, weighing them at the end of each day. Bryant found that bundles containing only half the resin concentration of natural twigs were left untouched. The avoidance of these unpalatable resins, he concludes, may play a significant role in the subsequent decline in the Lepus population to its normal level.
These results suggest obvious areas for further research. For example, observational data should be reviewed to see whether the periodic population explosions among the prolific lemming (like the vole and the snowshoe hare, a small rodent in a marginal northern environment) occur during years in which there is an early onset of vegetative growth; if so, a triggering mechanism similar to that found in the vole may be involved.
Bryant's interpretation of the results of his experiment (lines 46-48) depends on which of the following assumptions?

  1. The response of Lepus to resinous substances in nature may be different from its response under experimental conditions.
  2. The decennial rise in the Lepus population is triggered by an unknown phytochemical response.
  3. Many Lepus will starve to death rather than eat resinous shoots or change their diet.
  4. Lepus learns to search for alternative food sources once resinous shoots are encountered.

Answer(s): C

Explanation:

This question asks for the assumption upon which Bryant's interpretation rests. Bryant concluded from his experiment that avoidance of unpalatable resins in the natural food source of Lepus may play a role in the decline in the Lepus population. He is assuming that hares will not eat anything at all, and thus starve to death, if they find resin on their food. The gist of this is captured in Choice C.
Certainly Choice A is not an underlying assumption. Bryant's experiment would be worthless if the hares' behavior in the experiment didn't give us an idea of how they behaved in nature. Choice B is out because Bryant's experiment does not investigate the reasons for the decennial rise in hare population. Choice D makes no sense because if the hares learned to look for new sources of food once they couldn't eat the resinous shoots, their population wouldn't decrease.



One of the basic principles of ecology is that population size is to some extent a function of available food resources. Recent field experiments demonstrate that the interrelationship may be far more complex than hitherto imagined. Specifically, the browsing of certain rodents appears to trigger biochemical reactions in the plants they feed on that help regulate the size of the rodent populations. Two such examples of phytochemical regulation (regulation involving plant chemistry) have been reported so far.
Patricia Berger and her colleagues at the University of Utah have demonstrated that instrumentality of 6- methoxybenzoxazolinone (6-MBOA) in triggering reproductive behavior in the mountain vole (Microtus montanus), a small rodent resembling the field mouse. 6-MBOA forms in young mountain grasses in response to browsing by predators such as voles. The experimenters fed rolled oats coated with 6-MBOA to non- breeding winter populations of Microtus. After three weeks, the sample populations revealed a high incidence of pregnancy among the females and pronounced swelling of the testicles among the males. Control populations receiving no 6- MBOA revealed no such signs. Since the timing of reproductive effort is crucial to the short-lived vole in an environment in which the onset of vegetative growth can vary by as much as two months, the phytochemical triggering of copulatory behavior in Microtus represents a significant biological adaptation.
A distinct example is reported by John Bryant of the University of Alaska. In this case, plants seem to have adopted a form of phytochemical self-defense against the depredations of the snowshoe hare (Lepus americanus) of Canada and Alaska. Every ten years or so, for reasons that are not entirely understood, the Lepus population swells dramatically. The result is intense overbrowsing of early and mid-successional deciduous trees and shrubs. Bryant has shown that, as if in response, four common boreal forest trees favored by Lepus produce adventitious shoots high in terpene and phenolic resins which effectively discourage hare browsing. He treated mature, non-resinous willow twigs with resinous extracts from the adventitious shoots of other plants and placed treated and untreated bundles at hare feeding stations, weighing them at the end of each day. Bryant found that bundles containing only half the resin concentration of natural twigs were left untouched. The avoidance of these unpalatable resins, he concludes, may play a significant role in the subsequent decline in the Lepus population to its normal level.
These results suggest obvious areas for further research. For example, observational data should be reviewed to see whether the periodic population explosions among the prolific lemming (like the vole and the snowshoe hare, a small rodent in a marginal northern environment) occur during years in which there is an early onset of vegetative growth; if so, a triggering mechanism similar to that found in the vole may be involved.
The experiments performed by Berger and Bryant both study:

I). the effect of diet on reproduction in rodents
II). the relationship between food source and population size.
III). phytochemical phenomena in northern environments.

  1. II only
  2. III only
  3. I and II only
  4. II and III only

Answer(s): D

Explanation:

This Roman Numeral question is a bit reminiscent of question 112 in that you are once again considering what was or was not part of both studies. Statement I is not true because the effect of diet on reproduction is part of Berger's study only. Both studies investigate the relationship between food source and population size, so Statement II is true. Statement III is clearly true as well, so Choice D is the answer you want.



The anthropomorphic bias of those who would relegate marsupials to an inferior evolutionary status is most apparent in their recourse to data on brain structure and behavior. Unlike humans and other placentals, marsupials lack the corpus callosum, which facilitates inter-hemisphere transfer of data acquired through the senses. Yet it cannot be inferred that marsupials are thus deprived of such function. Didelphis Virginiana, one of the opossums, makes use of the anterior commissure, an adaptation that is also found in reptiles and monotremes. Diprodontons, including kangaroos and koalas, supplement the anterior commissure with the fasciculus aberrans. While the modes of neocortical interconnection may be diverse, the work of Johnson, Heath and Jones points to the conclusion that, functionally speaking the cortices and neocortices of both groups of mammals exhibit parallel connections. Parker also notes "a similar range of brain size to body weight ratios and of neocortical expansion".
Another stigma borne by marsupials is the consensus that they are less intelligent than placentals. Yet Williams argues that, all else being equal, natural selection will favor instinctive over learned behavior as being more biologically efficient and that it is the accidental death of the young that is the prime selective pressure for the evolution of intelligence. Seen in this light, marsupials have a competitive edge; their gestation period is brief and the young remain in the pouch for an extended period exposed only to those dangers which also affect the mother. There they are directly exposed to the mother's food supply and can observe her behavior at leisure. Placentals, on the other hand, not only have a longer gestation period but, once their young are born, must often leave while foraging. Such absences increase the risk of mortality and decrease the opportunity to learn. Thus, among placentals, selection would favor the apparent intelligence in the young and protective behavior in the mother.
Marsupials are not known to exhibit maternal protective behavior. In fact, Serventy has reported that frightened female kangaroos will drop their pouch-young as they flee, drawing a predator's attention to the less able offspring while the adult escapes. This behavior, whether purposeful or accidental, instantaneously relieves the female marsupial of the mechanical difficulties of pregnancy with which her placental counterpart would be burdened, while marsupials can replace any lost young quickly. Thus, in the absence of any need for close maternal supervision, sacrificing their offspring in this manner may well have been favored in selection. Pointing to the absence of the "virtue" of maternal protectiveness in marsupials is an instance of how mistaken are those theorists who see similarities with humans as marks of evolutionary sophistication.
The author's primary purpose in this passage is to:

  1. correct some common misconceptions about marsupials.
  2. argue against the view that marsupials represent a less developed evolutionary stage than placentals.
  3. provide support for the proposition that marsupials have adapted more successfully to the environment.
  4. determine the place of marsupials in the evolutionary hierarchy.

Answer(s): B

Explanation:

This is a main idea question. In this case, the first and last sentences of the passage are perfect book-ends summarizing the author's argument through the passage as a whole. The author is in disagreement with those who brand marsupials as inferior. Note that the word "argue" in this answer choice reflects the tone of the passage.
Choice A is wrong because the passage doesn't describe common misconceptions; it's about very specific disagreements on points concerning the evolutionary status of marsupials versus placentals.
Choice C is wrong because the passage doesn't deal directly with the question of environmental adaptation.
The word "determine" is the problem with incorrect answer choice D. This point is left open; by the end of the passage we're still not sure where marsupials fit into the evolutionary tree.



The anthropomorphic bias of those who would relegate marsupials to an inferior evolutionary status is most apparent in their recourse to data on brain structure and behavior. Unlike humans and other placentals, marsupials lack the corpus callosum, which facilitates inter-hemisphere transfer of data acquired through the senses. Yet it cannot be inferred that marsupials are thus deprived of such function. Didelphis Virginiana, one of the opossums, makes use of the anterior commissure, an adaptation that is also found in reptiles and monotremes. Diprodontons, including kangaroos and koalas, supplement the anterior commissure with the fasciculus aberrans. While the modes of neocortical interconnection may be diverse, the work of Johnson, Heath and Jones points to the conclusion that, functionally speaking the cortices and neocortices of both groups of mammals exhibit parallel connections. Parker also notes "a similar range of brain size to body weight ratios and of neocortical expansion".
Another stigma borne by marsupials is the consensus that they are less intelligent than placentals. Yet Williams argues that, all else being equal, natural selection will favor instinctive over learned behavior as being more biologically efficient and that it is the accidental death of the young that is the prime selective pressure for the evolution of intelligence. Seen in this light, marsupials have a competitive edge; their gestation period is brief and the young remain in the pouch for an extended period exposed only to those dangers which also affect the mother. There they are directly exposed to the mother's food supply and can observe her behavior at leisure. Placentals, on the other hand, not only have a longer gestation period but, once their young are born, must often leave while foraging. Such absences increase the risk of mortality and decrease the opportunity to learn. Thus, among placentals, selection would favor the apparent intelligence in the young and protective behavior in the mother.
Marsupials are not known to exhibit maternal protective behavior. In fact, Serventy has reported that frightened female kangaroos will drop their pouch-young as they flee, drawing a predator's attention to the less able offspring while the adult escapes. This behavior, whether purposeful or accidental, instantaneously relieves the female marsupial of the mechanical difficulties of pregnancy with which her placental counterpart would be burdened, while marsupials can replace any lost young quickly. Thus, in the absence of any need for close maternal supervision, sacrificing their offspring in this manner may well have been favored in selection. Pointing to the absence of the "virtue" of maternal protectiveness in marsupials is an instance of how mistaken are those theorists who see similarities with humans as marks of evolutionary sophistication.
According to the passage, which of the following favor(s) the development of intelligence as a trait of placental mammals?

I). The need to leave their young while foraging
II). The comparatively great risk of accidental death of the young
III). The opportunity for the young to observe the mother at leisure

  1. I only
  2. III only
  3. I and II only
  4. II and III only

Answer(s): C

Explanation:

This is a Roman numeral question, and the information we need to answer it is contained in the second paragraph. The last three sentences of that paragraph contain the most important information for our purposes.
There we are told that the placentals need to leave their young to go foraging; that immediately justifies statement I). We're told directly thereafter that this absence increases the risk of accidental death to the young.
Hence, we can justify statement II as well. Note: At this point, only choice C meets our needs, but don't ignore statement III! Statement III, on the other hand, applies only to marsupials. We are told that the absence of the mother while she forages decreases the opportunity for placentals to learn by observing the mother. Therefore, statement III is not true.Kaplan Strategy:Use "+" and "-" symbols to annotate true statements and false statements, respectively, on roman numeral questions. This will guide you to the correct answer choice more quickly and will also prevent you from having to read the question over and over again.



The anthropomorphic bias of those who would relegate marsupials to an inferior evolutionary status is most apparent in their recourse to data on brain structure and behavior. Unlike humans and other placentals, marsupials lack the corpus callosum, which facilitates inter-hemisphere transfer of data acquired through the senses. Yet it cannot be inferred that marsupials are thus deprived of such function. Didelphis Virginiana, one of the opossums, makes use of the anterior commissure, an adaptation that is also found in reptiles and monotremes. Diprodontons, including kangaroos and koalas, supplement the anterior commissure with the fasciculus aberrans. While the modes of neocortical interconnection may be diverse, the work of Johnson, Heath and Jones points to the conclusion that, functionally speaking the cortices and neocortices of both groups of mammals exhibit parallel connections. Parker also notes "a similar range of brain size to body weight ratios and of neocortical expansion".
Another stigma borne by marsupials is the consensus that they are less intelligent than placentals. Yet Williams argues that, all else being equal, natural selection will favor instinctive over learned behavior as being more biologically efficient and that it is the accidental death of the young that is the prime selective pressure for the evolution of intelligence. Seen in this light, marsupials have a competitive edge; their gestation period is brief and the young remain in the pouch for an extended period exposed only to those dangers which also affect the mother. There they are directly exposed to the mother's food supply and can observe her behavior at leisure. Placentals, on the other hand, not only have a longer gestation period but, once their young are born, must often leave while foraging. Such absences increase the risk of mortality and decrease the opportunity to learn. Thus, among placentals, selection would favor the apparent intelligence in the young and protective behavior in the mother.
Marsupials are not known to exhibit maternal protective behavior. In fact, Serventy has reported that frightened female kangaroos will drop their pouch-young as they flee, drawing a predator's attention to the less able offspring while the adult escapes. This behavior, whether purposeful or accidental, instantaneously relieves the female marsupial of the mechanical difficulties of pregnancy with which her placental counterpart would be burdened, while marsupials can replace any lost young quickly. Thus, in the absence of any need for close maternal supervision, sacrificing their offspring in this manner may well have been favored in selection. Pointing to the absence of the "virtue" of maternal protectiveness in marsupials is an instance of how mistaken are those theorists who see similarities with humans as marks of evolutionary sophistication.
The author's attitude toward those who consider marsupials to occupy an inferior evolutionary position would most probably be one of:

  1. criticism because they ignore evidence that marsupials are more intelligent than usually supposed.
  2. disagreement because current studies support the opposite view.
  3. disagreement because they apply human standards in an inappropriate context.
  4. agreement, but on the basis of marsupials' lack of maternal protective behavior rather than their brain structure.

Answer(s): C

Explanation:

The answers break down into two parts ­ first, there is the author's attitude; second, there are the reasons for that attitude, which are going to test our ability to follow the logical progression of the passage. Choice D can be eliminated immediately because we know that the author does not support this view.
The point made in choice C echoes throughout the passage from the anthropomorphic bias of the first sentence to the point made in the last sentence in the passage. The context is inappropriate because the author seems to feel that what serves placentals, including humans, in the evolutionary sense, does not necessary serve marsupials.
Choice A misses the point of the passage. No such evidence is cited.
Choice B is wrong because it suggests that marsupials occupy a superior evolutionary position based on current studies. This is not correct.



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