What is life?
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What is life?
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[post_date] => 2025-01-03 12:45:42
[post_date_gmt] => 2025-01-03 17:45:42
[post_content] => Practice Passage (Question 1-6)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
The greatest problem of biology is understanding the divide that exists between life and matter. There seems to be an unbridgeable gulf between them, but how could life have emerged from matter if it is fundamentally different from it? The received view, today, is that life is but an extremely complex form of chemistry, which is equivalent to saying that there is no fundamental divide between them. Primordial genes and primordial proteins appeared spontaneously on the primitive Earth and gradually evolved into increasingly more complex structures, all the way up to the first cells, the basic units of life. The problem of which molecules came first has been the object of countless debates, but in a way it is a secondary issue. What really matters is that spontaneous genes and spontaneous proteins had the potential to evolve into the first cells. This however, is precisely what molecular biology does not support.
The genes and proteins of the first cells had to have biological specificity, and specific molecules cannot be formed spontaneously. They can only be manufactured by molecular machines, and their production requires entities like sequences and codes that simply do not exist in spontaneous processes. That is what really divides matter from life. All components of matter arise by spontaneous processes that do not require sequences and codes, whereas all components of life arise by manufacturing processes that do require these entities. It is the signaling of these sequences and codes, or semiosis, that makes the difference between life and matter. It is semiosis that does not exist in the inanimate world, and that is why biology is not a complex form of chemistry.
The problem of the origin of life becomes in this way the problem of understanding how the first molecular machines came into existence and started producing new types of molecules. We have seen that chemical evolution could spontaneously produce ‘bondmakers’, molecules that had the ability to stick subunits together, and we have also seen that some bondmakers could become ‘copymakers’ by sticking subunits together in the order provided by a template. The next step was the appearance of ‘codemakers’, and that is much more difficult to account for, but in principle it has the same logic and we can regard it as a natural event (ribosomes, for example, can still arise by self-assembly from their components). What really matters is that molecular machines could arise spontaneously, and once in existence they started producing molecules that cannot be formed spontaneously. More precisely, they started producing specific genes and specific proteins and that is what crossed the gulf that divides inanimate matter from life.
The genetic code was the first organic code in the history of life, but was not the only one. We have seen that other organic codes came into existence, and that they account not only for the production of new biological objects but also for the organization of these objects into higher structures and for their interactions with the external world. Semiosis, in short, was not limited to the production of specific molecules. There are at least three different types of semiosis in Nature and we find codes at all levels of life, from the world of genes and proteins all the way up to mind and language. Physics and chemistry provide of course the building blocks of life, but what ‘animates’ matter is codes, and that is why there is a deep truth in the oversimplified statement that “life is semiosis”.
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[questions] => Array
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[question] => It can be inferred from the passage that in the scientific community the author’s definition of life is:
[value] => Array
(
[answer] => 2
[description] => Reason for the Correct Answer:
This is a “Foundations of Comprehension” question which is asking you to recognize an accurate paraphrase or summary of the central theme or of particular statements in the passage, or to interpret word choices made by the author.
The passage author clearly does not believe that the definition of life is fairly unimportant (option 4) because, in paragraph 1, the author writes, “The greatest problem of biology is understanding the divide that exists between life and matter.” We can infer that the author’s view of life is not widely accepted (option 1) from paragraph 1, where the author presents the “received” view that life is defined as an “extremely complex form of chemistry, which is equivalent to saying that there is no fundamental divide between them.” At the end of paragraph 2, the author explicitly states that life is not just a complex form of chemistry, which shows that the author does not subscribe to the widely received view introduced in paragraph 1. Instead, the author juxtaposes his alternative view of life (option 2) in paragraph 2 as arising from manufacturing processes that do not occur spontaneously. The author explicitly notes that the order of which molecules came first is a different issue (option 3).
Option 2 is correct.
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[answers] => Array
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[0] => Array
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[each_answer] => A. widely accepted
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[1] => Array
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[each_answer] => B. an alternative perspective
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[2] => Array
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[each_answer] => C. part of the controversy over which molecules came first
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[3] => Array
(
[each_answer] => D. fairly unimportant
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[1] => Array
(
[quiz_unique_key] => 3873426850
[question] => In paragraph 3, the author most likely mentions ‘bondmakers,’ ‘copymakers,’ and ‘codemakers,’ in order to:
[value] => Array
(
[answer] => 1
[description] => Reason for the Correct Answer:
This is a “Reasoning Within the Text” question, which means that it directs your attention to an argument, claim, or theme presented in the passage, and tests your ability to analyze and evaluate the strength of evidentiary relationships among component parts of an argument.
While the author rejects the idea that life should be defined according to chemical complexity, the author never argues that molecular sequencing is not a complex process (option 2). In paragraph 4, the reference to at least three different types of semiosis (option 3) is merely to underscore that there are “codes at all levels of life, from the world of genes and proteins all the way up to mind and language.” The reference is unrelated to the bondmakers, copymakers, and codemakers. Finally, the author points out in paragraph 3 that bondmakers, copymakers, and codemakers are molecules that are essential for coded processes such as sticking subunits together (paragraph 3). Although the author mentions that these molecular machines are spontaneously produced (option 4), this is not central to the main argument which is that they execute non-spontaneous processes essential to living organisms (option 1).
Option 1 is correct.
)
[answers] => Array
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[0] => Array
(
[each_answer] => A. Offer examples of molecular machines that are essential to life.
)
[1] => Array
(
[each_answer] => B. Rebut the common scientific view that molecular sequencing is a complex process.
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[2] => Array
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[each_answer] => C. Illustrate there are at least three different types of semiosis that exist in Nature.
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[3] => Array
(
[each_answer] => D. Emphasize that components of matter arise by spontaneous processes.
)
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[2] => Array
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[quiz_unique_key] => 83407773
[question] => The author’s central message for the whole passage is BEST summarized as:
[value] => Array
(
[answer] => 2
[description] => Reason for the Correct Answer:
This is a “Foundations of Comprehension” question which is asking you to recognize an accurate paraphrase or summary of the central theme or of particular statements in the passage, or to interpret word choices made by the author.
In paragraph 1, the author explains how it is thought that the first cells evolved from spontaneous genes and spontaneous proteins (option 1), and then goes on to say, “This however, is precisely what molecular biology does not support.” In the second paragraph, the author argues that what really divides life from matter is that life requires sequences and codes that are required to give rise to certain molecules and proteins (option 2), but are not required in non-living matter The author never argues that life does not have complex chemical processes at all (option 3). Finally, the author states that while molecular machines allow for non-spontaneous processes, these machines are still themselves the outcome of spontaneous and natural chemical processes, with no implication of being directed by an intelligence (option 4).
Option 2 is correct.
)
[answers] => Array
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[0] => Array
(
[each_answer] => A. Spontaneous genes and spontaneous proteins evolved into the first cells on earth.
)
[1] => Array
(
[each_answer] => B. What divides matter and life requires sequences and codes.
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[2] => Array
(
[each_answer] => C. Life is not made up of complex chemical processes requiring sequences and codes.
)
[3] => Array
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[each_answer] => D. Life requires a process directed by intelligence.
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[3] => Array
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[quiz_unique_key] => 872728905
[question] => Which of the following is LEAST analogous to the semiosis described in paragraph 4 and throughout the passage?
[value] => Array
(
[answer] => 3
[description] => Reason for the Correct Answer:
This is a “Reasoning Beyond the Text” question, which means that it wants you to either apply or extrapolate the ideas in the passage to new situations or to assess how new information would impact the ideas presented in the passage. It is important to understand the assumptions underlying the article, and how new information may or may not shift the central thesis.
The end of paragraph 4 states that “life is semiosis.” The central message of the passage is that coded sequences and directed patterns are what define life. Semiotics actually means, “the study of signs,” but even if you didn’t know that, you can infer from the passage that semiosis is referring to patterns of meaning in nature (codes and sequences.) A device programmed to carry out operations (option 1), a chain stitch on a Persian rug (option 2), and a figure-eight dance used by honey bees to communicate are all examples of things that involve specific predictable patterns. The assorted gases expelled from a volcanic vent (option 3) are more chaotic, and are the least analogous to the semiotic notion of order and higher organization.
Option 3 is correct.
)
[answers] => Array
(
[0] => Array
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[each_answer] => A. A device programmed to carry out a set of logical operations.
)
[1] => Array
(
[each_answer] => B. Traditional embroidery in chain stitch on a Persian rug.
)
[2] => Array
(
[each_answer] => C. Assorted gases expelled from a volcanic vent.
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[3] => Array
(
[each_answer] => D. A figure-eight dance used by honey bees to communicate.
)
)
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[4] => Array
(
[quiz_unique_key] => 3143847772
[question] => Suppose scientists discover a spongy substance on the bottom of the ocean that appears to eat small fish, expel waste, reproduce, and eventually die. The spongy substance does not contain any components that require coding or sequencing. Based on the passage, the author is most likely to classify the discovery as:
[value] => Array
(
[answer] => 4
[description] => Reason for the Correct Answer:
This is a “Reasoning Beyond the Text” question, which means that it wants you to either apply or extrapolate the ideas in the passage to new situations or to assess how new information would impact the ideas presented in the passage. It is important to understand the assumptions underlying the article, and how new information may or may not shift the central thesis.
The best answer must consider that the author would classify the spongy substance based on the fact that its components do not require sequences and codes. The author writes that when molecular production requires entities “like sequences and codes that simply do not exist in spontaneous processes… that is what really divides matter from life.” Thus, only life, which would include primordial life, requires sequences and codes (options 1 and 2) while matter does not (option 4). The author does not provide definitions for the term “Primordial life” (option 1). Since the spongy substance does not contain any components that require coding or sequencing, the author would not infer that this non-living matter resulted from non-spontaneous processes (option 3).
Option 4 is correct.
)
[answers] => Array
(
[0] => Array
(
[each_answer] => A. Primordial life
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[1] => Array
(
[each_answer] => B. Life
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[2] => Array
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[each_answer] => C. The result of non-spontaneous processes
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[3] => Array
(
[each_answer] => D. Matter
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[5] => Array
(
[quiz_unique_key] => 3143847772
[question] => Which of the following assumptions must the author make to preserve the logic of his main argument:
[value] => Array
(
[answer] => 3
[description] => Reason for the Correct Answer:
This is a “Reasoning Within the Text” question. These items generally ask you to think about the author’s reasoning, such as what claim an author is trying to support with a piece of evidence, what assumption underlies a specific statement, or whether an argument is flawed.
The author argues in paragraph 1 that there is a gulf between matter and life, because how can matter, which is fundamentally different than life, give rise to life? The author then claims to have bridged the gulf by the end of the passage by arguing that life is comprised of components that can only be made from coded and sequenced processes, while matter contains components that are more random and spontaneous. Thus, he is clearly not assuming that all molecules have codes (option 1). The timespan of chemical evolution (option 2) is not relevant to the author’s argument. While the author states that the genetic code was the first organic code (option 4), this is an isolated fact that serves no critical logical role in the argument. In paragraph 2, the author states that “specific molecules do not arise spontaneously”, and then in paragraph 3 states that “molecular machines could arise spontaneously.” These statements would be contradictory, unless the author was assuming that molecular machines are not “specific molecules” (option 3).
Option 3 is correct.
)
[answers] => Array
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[0] => Array
(
[each_answer] => A. Codes can be found in all molecules.
)
[1] => Array
(
[each_answer] => B. Chemical evolution happens over extended time periods.
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[2] => Array
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[each_answer] => C. Molecular machines are not specific molecules.
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[3] => Array
(
[each_answer] => D. Genetic codes were among the first organic codes.
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[559780|1] => B
[559780|2] => A
[559780|3] => B
[559780|4] => C
[559780|5] => D
[559780|6] => C
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