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Medical College Admission Test: Verbal Reasoning, Biological Sciences, Physical Sciences, Writing Sample (Page 13 )

Updated On: 7-Oct-2026
Page 13 of 164
PDF with 811 Questions

Studies of photosynthesis began in the late eighteenth century. One scientist found that green plants produce a substance (later shown to be oxygen) that supports the flame of a candle in a closed container. Several years later it was discovered that a plant must be exposed to light in order to replenish this flame-sustaining "substance". Soon another discovery showed that the oxygen is formed at the expense of another gas, carbon dioxide.
In 1804, de Saussure conducted experiments revealing that equal volumes of carbon dioxide and oxygen are exchanged between a plant and the air surrounding it. De Saussure determined that the weight gained by a plant grown in a pot equals the sum of the weights of carbon derived from absorbed carbon dioxide and water absorbed through plant roots. Using this information, de Saussure was able to postulate that in photosynthesis carbon dioxide and water combine using energy in the form of light to produce carbohydrates, water, and free oxygen. Much later, in 1845, scientists' increased understanding of concepts of chemical energy led them to perceive that, through photosynthesis, light energy is transformed and stored as chemical energy.
In the twentieth century, studies comparing photosynthesis in green plants and in certain sulfur bacteria yielded important information about the photosynthetic process. Because water is both a reactant and a product in the central reaction, it had long been assumed that the oxygen released by photosynthesis comes from splitting the carbon dioxide molecule. In the 1930s, however, this popular view was decisively altered by the studies of C. B. Van Niel. Van Niel studied sulfur bacteria, which use hydrogen sulfide for photosynthesis in the same way that green plants use water, and produce sulfur instead of oxygen. Van Niel saw that the use of carbon dioxide to form carbohydrates was similar in the two types of organisms. He reasoned that the oxygen produced by green plants must derive from water ­ rather than carbon dioxide, as previously assumed ­ in the same way that the sulfur produced by the bacteria derives from hydrogen sulfide. Van Niel's finding was important because the earlier belief had been that oxygen was split off from carbon dioxide, and that carbon then combined with water to form carbohydrates. The new postulate was that, with green plants, hydrogen is removed from water and then combines with carbon dioxide to form the carbohydrates needed by the organism.
Later, Van Niel's assertions were strongly backed by scientists who used water marked with a radioactive isotope of oxygen in order to follow photosynthetic reactions. When the photosynthetically-produced free oxygen was analyzed, the isotope was found to be present.
According to the passage, C. B. Van Niel's experiments:

  1. provided the first model of photosynthesis.
  2. showed that the carbon dioxide molecule is split during photosynthesis.
  3. proved that some organisms combine hydrogen sulfide with carbon dioxide in photosynthesis.
  4. provided evidence that weakened the accepted model of photosynthesis.

Answer(s): D

Explanation:

This is a detail question regarding Van Niel's experiments. Van Niel's work is discussed in paragraph 3. The first three and final two sentences of the paragraph make it clear that Van Niel's studies "decisively altered" the traditional model of the photosynthetic reaction and supported a substitute conception. This idea is paraphrased in choice (D), making choice (D) correct.de Saussure worked with a model of photosynthesis back in the early nineteenth century ­ a full century before Van Niel ­ so choice (A) is incorrect. Choice (B) summarizes an assumption that Van Niel disproved. Choice (B) is incorrect. As for choice (C), the passage never states that Van Niel discovered or proved that sulfur bacteria used hydrogen sulfide, merely that Van Niel studied these bacteria in order to make inferences about photosynthesis in green plants. In all likelihood it was another scientist who saw that these organisms used hydrogen sulfide to make their food.



Studies of photosynthesis began in the late eighteenth century. One scientist found that green plants produce a substance (later shown to be oxygen) that supports the flame of a candle in a closed container. Several years later it was discovered that a plant must be exposed to light in order to replenish this flame-sustaining "substance." Soon another discovery showed that the oxygen is formed at the expense of another gas, carbon dioxide.
In 1804, de Saussure conducted experiments revealing that equal volumes of carbon dioxide and oxygen are exchanged between a plant and the air surrounding it. De Saussure determined that the weight gained by a plant grown in a pot equals the sum of the weights of carbon derived from absorbed carbon dioxide and water absorbed through plant roots. Using this information, de Saussure was able to postulate that in photosynthesis carbon dioxide and water combine using energy in the form of light to produce carbohydrates, water, and free oxygen. Much later, in 1845, scientists' increased understanding of concepts of chemical energy led them to perceive that, through photosynthesis, light energy is transformed and stored as chemical energy.
In the twentieth century, studies comparing photosynthesis in green plants and in certain sulfur bacteria yielded important information about the photosynthetic process. Because water is both a reactant and a product in the central reaction, it had long been assumed that the oxygen released by photosynthesis comes from splitting the carbon dioxide molecule. In the 1930s, however, this popular view was decisively altered by the studies of C. B. Van Niel. Van Niel studied sulfur bacteria, which use hydrogen sulfide for photosynthesis in the same way that green plants use water, and produce sulfur instead of oxygen. Van Niel saw that the use of carbon dioxide to form carbohydrates was similar in the two types of organisms. He reasoned that the oxygen produced by green plants must derive from water ­ rather than carbon dioxide, as previously assumed ­ in the same way that the sulfur produced by the bacteria derives from hydrogen sulfide. Van Niel's finding was important because the earlier belief had been that oxygen was split off from carbon dioxide, and that carbon then combined with water to form carbohydrates. The new postulate was that, with green plants, hydrogen is removed from water and then combines with carbon dioxide to form the carbohydrates needed by the organism.
Later, Van Niel's assertions were strongly backed by scientists who used water marked with a radioactive isotope of oxygen in order to follow photosynthetic reactions. When the photosynthetically-produced free oxygen was analyzed, the isotope was found to be present.
According to the passage, the study of organisms that require hydrogen sulfide for photosynthesis:

  1. proved that oxygen is not produced in photosynthesis.
  2. contradicted the notion that oxygen is needed to support a candle's flame.
  3. disproved assumptions about the role of light energy in photosynthesis.
  4. clarified the role of water in photosynthesis among green plants.

Answer(s): D

Explanation:

This also refers to Van Niel's study. Paragraph 3 explains that Van Niel's investigation led to his conclusion that water plays a much different role in photosynthesis than had long been assumed ­ that water (rather than carbon dioxide) is split, into hydrogen and oxygen. The point is paraphrased in choice (D), making choice (D) correct. Choice (A) is incorrect because, although oxygen isn't produced in the photosynthetic process occurring in the bacteria, it certainly is produced by green plant photosynthesis. Van Niel's study showed exactly where oxygen comes from in green plant photosynthesis. As for choice (B), Van Niel's study had nothing to do with a candle flame; that's an irrelevant detail from the eighteenth century, noted in paragraph 1.
Similarly, the role of light in photosynthesis as mentioned in choice (C), is never questioned.



Studies of photosynthesis began in the late eighteenth century. One scientist found that green plants produce a substance (later shown to be oxygen) that supports the flame of a candle in a closed container. Several years later it was discovered that a plant must be exposed to light in order to replenish this flame-sustaining "substance". Soon another discovery showed that the oxygen is formed at the expense of another gas, carbon dioxide.
In 1804, de Saussure conducted experiments revealing that equal volumes of carbon dioxide and oxygen are exchanged between a plant and the air surrounding it. De Saussure determined that the weight gained by a plant grown in a pot equals the sum of the weights of carbon derived from absorbed carbon dioxide and water absorbed through plant roots. Using this information, de Saussure was able to postulate that in photosynthesis carbon dioxide and water combine using energy in the form of light to produce carbohydrates, water, and free oxygen. Much later, in 1845, scientists' increased understanding of concepts of chemical energy led them to perceive that, through photosynthesis, light energy is transformed and stored as chemical energy.
In the twentieth century, studies comparing photosynthesis in green plants and in certain sulfur bacteria yielded important information about the photosynthetic process. Because water is both a reactant and a product in the central reaction, it had long been assumed that the oxygen released by photosynthesis comes from splitting the carbon dioxide molecule. In the 1930s, however, this popular view was decisively altered by the studies of C. B. Van Niel. Van Niel studied sulfur bacteria, which use hydrogen sulfide for photosynthesis in the same way that green plants use water, and produce sulfur instead of oxygen. Van Niel saw that the use of carbon dioxide to form carbohydrates was similar in the two types of organisms. He reasoned that the oxygen produced by green plants must derive from water ­ rather than carbon dioxide, as previously assumed ­ in the same way that the sulfur produced by the bacteria derives from hydrogen sulfide. Van Niel's finding was important because the earlier belief had been that oxygen was split off from carbon dioxide, and that carbon then combined with water to form carbohydrates. The new postulate was that, with green plants, hydrogen is removed from water and then combines with carbon dioxide to form the carbohydrates needed by the organism.
Later, Van Niel's assertions were strongly backed by scientists who used water marked with a radioactive isotope of oxygen in order to follow photosynthetic reactions. When the photosynthetically-produced free oxygen was analyzed, the isotope was found to be present.
Which of the following statements about photosynthesis would most probably NOT have been made by de Saussure?

  1. It involves an exchange of equal quantities of gases.
  2. It results in the conversion of light energy to chemical energy.
  3. It produces oxygen.
  4. It requires light.

Answer(s): B

Explanation:

This is an inference question, which asks for the identification of a statement that probably would not have been made by de Saussure in relation to photosynthesis. De Saussure is discussed in the second paragraph.
According to the last sentence of the paragraph, the conversion of light energy into chemical energy was not well understood until after de Saussure's work. According to the previous sentence, de Saussure was aware only that light supplied energy to plants. So it's unlikely that the statement made in choice (B) would have been made by de Saussure. Each of the other choices is mentioned earlier in this paragraph or in paragraph 1 as having been known to or discovered by de Saussure.



Studies of photosynthesis began in the late eighteenth century. One scientist found that green plants produce a substance (later shown to be oxygen) that supports the flame of a candle in a closed container. Several years later it was discovered that a plant must be exposed to light in order to replenish this flame-sustaining "substance." Soon another discovery showed that the oxygen is formed at the expense of another gas, carbon dioxide.
In 1804, de Saussure conducted experiments revealing that equal volumes of carbon dioxide and oxygen are exchanged between a plant and the air surrounding it. De Saussure determined that the weight gained by a plant grown in a pot equals the sum of the weights of carbon derived from absorbed carbon dioxide and water absorbed through plant roots. Using this information, de Saussure was able to postulate that in photosynthesis carbon dioxide and water combine using energy in the form of light to produce carbohydrates, water, and free oxygen. Much later, in 1845, scientists' increased understanding of concepts of chemical energy led them to perceive that, through photosynthesis, light energy is transformed and stored as chemical energy.
In the twentieth century, studies comparing photosynthesis in green plants and in certain sulfur bacteria yielded important information about the photosynthetic process. Because water is both a reactant and a product in the central reaction, it had long been assumed that the oxygen released by photosynthesis comes from splitting the carbon dioxide molecule. In the 1930s, however, this popular view was decisively altered by the studies of C. B. Van Niel. Van Niel studied sulfur bacteria, which use hydrogen sulfide for photosynthesis in the same way that green plants use water, and produce sulfur instead of oxygen. Van Niel saw that the use of carbon dioxide to form carbohydrates was similar in the two types of organisms. He reasoned that the oxygen produced by green plants must derive from water ­ rather than carbon dioxide, as previously assumed ­ in the same way that the sulfur produced by the bacteria derives from hydrogen sulfide. Van Niel's finding was important because the earlier belief had been that oxygen was split off from carbon dioxide, and that carbon then combined with water to form carbohydrates. The new postulate was that, with green plants, hydrogen is removed from water and then combines with carbon dioxide to form the carbohydrates needed by the organism.
Later, Van Niel's assertions were strongly backed by scientists who used water marked with a radioactive isotope of oxygen in order to follow photosynthetic reactions. When the photosynthetically-produced free oxygen was analyzed, the isotope was found to be present.
The passage supplies information for answering all of the following questions EXCEPT:

  1. Why is oxygen necessary for a candle to burn?
  2. What was de Saussure's explanation of the function of water in photosynthesis?
  3. What is the function of light in photosynthesis?
  4. Is water required for all photosynthetic reactions?

Answer(s): A

Explanation:

This asks the reader to identify the question that's not answered in this passage. The question that's never answered in the passage is choice (A): it's never explained why (or how) oxygen supports a candle flame, or any other kind of combustion. Each of the other questions does get answered. Regarding choice (B), de Saussure claimed that water's function in photosynthesis is to combine with carbon dioxide as stated in the middle of paragraph 2. For choice (C), light is described, in the last couple of sentences of paragraph 2, as being the energy source for photosynthesis. Choice (D) can be found in paragraph 3; water is not used by those bacteria that use hydrogen sulfide.



Although nihilism is commonly defined as a form of extremist political thought, the term has a broader meaning. Nihilism is in fact a complex intellectual stance with venerable roots in the history of ideas, which forms the theoretical basis for many positive assertions of modern thought. Its essence is the systematic negation of all perceptual orders and assumptions. A complete view must account for the influence of two historical crosscurrents: philosophical skepticism about the ultimacy of any truth, and the mystical quest for that same pure truth. These are united by their categorical rejection of the "known."
The outstanding representative of the former current, David Hume (1711-1776), maintained that external reality is unknowable, since sense impressions are actually part of the contents of the mind. Their presumed correspondence to external "things" cannot be verified, since it can be checked only by other sense impressions. Hume further asserts that all abstract conceptions turn out, on examination, to be generalizations from sense impressions. He concludes that even such an apparently objective phenomenon as a cause-and- effect relationship between events may be no more than a subjective fabrication of the observer. Stanley Rosen notes: "Hume terminates in skepticism because he finds nothing within the subject but individual impressions and ideas."
For mystics of every faith, the "experience of nothingness" is the goal of spiritual practice. Buddhist meditation techniques involve the systematic negation of all spiritual and intellectual constructs to make way for the apprehension of pure truth. St. John of the Cross similarly rejected every physical and mental symbolization of God as illusory. St. John's spiritual legacy is, as Michael Novak puts it, "the constant return to inner solitude, an unbroken awareness of the emptiness at the heart of consciousness. It is a harsh refusal to allow idols to be placed in the sanctuary. It requires also a scorching gaze upon all the bureaucracies, institutions, manipulators, and hucksters who employ technology and its supposed realities to bewitch and bedazzle the psyche."
Novak's interpretation points to the way these philosophical and mystical traditions prepared the ground for the political nihilism of the nineteenth and twentieth centuries. The rejection of existing social institutions and their claims to authority is in the most basic sense made possible by Humean skepticism. The political nihilism of the Russian intelligentsia combined this radical skepticism with a near mystical faith in the power of a new beginning. Hence, their desire to destroy becomes a revolutionary affirmation; in the words of Stanley Rosen, "Nihilism is an attempt to overcome or repudiate the past on behalf of an unknown and unknowable, yet hoped- for, future". This fusion of skepticism and mystical re-creation can be traced in contemporary thought, for example as an element in the counterculture of the 1960s.
The author's working definition of "nihilism", as it functions in the passage, is:

  1. systematic doubt of that which one takes for granted.
  2. a mystical quest for nothingness.
  3. a form of extremist political thought.
  4. rejection of all presently established institutions.

Answer(s): A

Explanation:

This question asks you for the author's working definition of "nihilism". Remember that the author's definition is not necessarily the same as the usual definition of nihilism, a form of extremist political thought, so C is not correct. The definition that reflects the author's own thinking is provided in the second and third sentences of Paragraph 1. The author says there that nihilism is a complex intellectual stance whose essence is systematic negation of perceptual orders and assumptions. This points to Choice A as the correct answer.
Choice B defines the essence of mysticism, not nihilism. Choice D is too narrow, being an aspect of political nihilism derived purely from skepticism.



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