4.  Science Passages

Intro (0:01) | Passage Map (4:33) | Ex. 1 (7:13) | Ex. 2 (10:12) | Ex. 3 (12:01) | Summary (16:15)
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Essay Walkthrough (Medium)

Q. 3

Q. 7

Sample Essay (Medium)

Nearly twenty years ago, biochemists found that a separable constituent of deoxyribonucleic acid (or DNA) appeared to guide the cell’s protein-synthesizing machinery. The internal structure of DNA seemed to represent a set of coded instructions which dictated the pattern of protein-synthesis. Experiments indicated that in the presence of appropriate enzymes each DNA molecule could form a replica, a new DNA molecule, containing the specific guiding message present in the original. This idea, when added to what was already known about the cellular mechanisms of heredity (especially the knowledge that DNA is localized in chromosomes), appeared to establish a molecular basis for inheritance.

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Paragraph 1 Analysis

Nearly twenty years ago, biochemists found that a separable constituent of deoxyribonucleic acid (or DNA) appeared to guide the cell’s protein-synthesizing machinery. The internal structure of DNA seemed to represent a set of coded instructions which dictated the pattern of protein-synthesis. Experiments indicated that in the presence of appropriate enzymes each DNA molecule could form a replica, a new DNA molecule, containing the specific guiding message present in the original. This idea, when added to what was already known about the cellular mechanisms of heredity (especially the knowledge that DNA is localized in chromosomes), appeared to establish a molecular basis for inheritance.

The first paragraph here is actually mostly fluff. This is a scientific background that prepares readers for the controversy ahead. Don’t get intimidated. Skim over this type of writing. If you don’t understand all of the jargon the first time through, don’t panic and re-read too much. On long essays like this you can’t get bogged down.

Proponents of the theory that DNA was a “self-duplicating” molecule, containing a code that by itself determined biological inheritance, introduced the term “central dogma” into scientific literature. They did so in order to describe the principles that could explain DNA’s governing role. The dogma originally involved an admittedly unproven assumption that, whereas nucleic acids can guide the synthesis of other nucleic acids and of proteins, the reverse effect is impossible; that is, proteins cannot guide the synthesis of nucleic acids. But actual experimental observations deny the second and crucial part of this assumption. Other test-tube experiments show that agents besides DNA have a guiding influence. The kind of protein that is made may depend on the specific organism from which the necessary enzyme is obtained. It also depends on the test tube’s temperature, the degree of acidity, and the amount of metallic salts present.

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Paragraph 2 Analysis

Proponents of the theory that DNA was a “self-duplicating” molecule, containing a code that by itself determined biological inheritance, introduced the term “central dogma” into scientific literature. They did so in order to describe the principles that could explain DNA’s governing role. The dogma originally involved an admittedly unproven assumption that, whereas nucleic acids can guide the synthesis of other nucleic acids and of proteins, the reverse effect is impossible; that is, proteins cannot guide the synthesis of nucleic acids. But actual experimental observations deny the second and crucial part of this assumption. Other test-tube experiments show that agents besides DNA have a guiding influence. The kind of protein that is made may depend on the specific organism from which the necessary enzyme is obtained. It also depends on the test tube’s temperature, the degree of acidity, and the amount of metallic salts present.

When you see “dogma” or some other somewhat derogatory term, the author is bringing his or her opinion into the essay. Start reading slowly. You are getting to the good part. You have just found the central point of the essay. Like Galileo using the movements of the planets to rail against the established orthodoxy of his time, our author seeks to use his experimental observations to challenge the “dogma.” This essay is describing a conflict between dogma and actual experimental evidence. This conflict is likely to come up later in the questions, because it deals with the author’s opinion and argument.

The central dogma banishes from consideration the interactions among the numerous molecular processes that have been discovered in cells or in their extracted fluids. In the living cell, molecular processes – the synthesis of nucleic acids and proteins or the oxidation of food substance – are not separate but interact in exceedingly complex ways. No matter how many ingredients the biochemists’ test tubes may contain, the mixtures are nonliving. However, these same ingredients, organized by the subtle structure of the cell, constitute a system, which is alive.

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Paragraph 3 Analysis

The central dogma banishes from consideration the interactions among the numerous molecular processes that have been discovered in cells or in their extracted fluids. In the living cell, molecular processes – the synthesis of nucleic acids and proteins or the oxidation of food substance – are not separate but interact in exceedingly complex ways. No matter how many ingredients the biochemists’ test tubes may contain, the mixtures are nonliving. However, these same ingredients, organized by the subtle structure of the cell, constitute a system, which is alive.

Now the author really begins to make his point and he uses strong language: “dogma banishes from consideration the interactions among the numerous molecular processes that have been discovered in cells or in their extracted fluids.” He is stating a simple vs. complex conflict: the simplicity of the “dogma” and the complexity of his understanding of the cell. The theme can be likened to the simple versus the more complex.

Consider an example from another field. At ordinary temperatures, electricity flows only so long as a driving force from a battery or generator is imposed upon the circuit. At temperatures near absolute zero, metals exhibit superconductivity: a unique property that causes an electric current to flow for months after the voltage is cut off. Although independent electrons exist in a metal at ordinary temperatures, at very low temperatures they interact with the metal’s atomic structure in such a way as to lose their individual identities and form a coordinated, collective system which gives rise to superconductivity.

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Paragraph 4 Analysis

Consider an example from another field. At ordinary temperatures, electricity flows only so long as a driving force from a battery or generator is imposed upon the circuit. At temperatures near absolute zero, metals exhibit superconductivity: a unique property that causes an electric current to flow for months after the voltage is cut off. Although independent electrons exist in a metal at ordinary temperatures, at very low temperatures they interact with the metal’s atomic structure in such a way as to lose their individual identities and form a coordinated, collective system which gives rise to superconductivity.

The author is making an analogy between the complexity of metals and that of the cell’s molecular structure. The author does so just to make sure you really understand how complex cells are.

Such discoveries of modern physics show that the unique properties of a complex system are not necessarily explicable solely by the properties that can be observed in its isolated parts. We can expect to find a similar situation in the complex chemical system of the living cells.

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Paragraph 5 Analysis

Such discoveries of modern physics show that the unique properties of a complex system are not necessarily explicable solely by the properties that can be observed in its isolated parts. We can expect to find a similar situation in the complex chemical system of the living cells.

The author continues to explain that physical systems are more complicated than they appear. Because the author has dwelled on this concept for quite a long time, you can be sure it will reappear in the questions.

Passage Analysis

1. What is the passage type?

Explanation

Subject: Science

Action: Persuade

2. What is each paragraph about?

Explanation

P1: DNA is the molecular basis of inheritance.
P2: DNA does not act alone. The reality is more complicated.
P3: Cells are really complicated and the parts work together.
P4: Metals are complicated and the parts work together (just like in cells).
P5: Cells are complicated and highly coordinated systems.

3. What is the organization?

Explanation

This is a theory / counter-theory passage.

Old Theory:

Problem with theory:

Implication of problem:

Explanatory analogy:

Summary:

Protein synthesis is a simple matter of DNA.

Other agents influence protein synthesis.

Cells are complicated, coordinated systems.

Example of superconductivity metals.

Cells are complicated, coordinated systems.

4. What is the big idea?

Explanation

Cells are so complex that the current theory doesn’t do them justice.

5 . What is the author’s purpose?

Explanation

The author takes issue with an old theory about cells and introduces a new theory as an alternative.

Passage Questions

1. The author primarily is concerned with:

A) proposing that a new philosophical foundation for modern biochemistry be developed.
B) describing the various processes that take place in a living cell.
C) drawing analogies between different scientific fields.
D) revealing a discrepancy between a scientific theory and some experimental results.
E) questioning the assumptions behind experimental methods in science.

Type: Main Idea

(D) The third sentence in the second paragraph tells us that the author’s primary concern is that actual experimental observations deny the assumptions of scientific theory. (“But actual experimental observations deny the second and crucial part of this assumption.”). The last paragraph emphasizes this discrepancy. This question asks you to find the best summary of the author’s ideas, and therefore requires an understanding of the passage as a whole.

2. The author provides information that would answer which of the following questions?

I. What have test-tube experiments revealed about the role of DNA?
II. What viruses interfere with DNA replication?
III. What methods have been developed to allow scientists to observe a living cell?

A) I only
B) II only
C) I and III only
D) II and III only
E) I, II and III

Type: Detail of the passage

(A) The first option, “What have test-tube experiments revealed about the role of DNA,” is supported by the passage in the second paragraph. No information is provided for the other options. This question requires one to look back to the passage for evidence of each choice.

3. The author’s argument is directed against which of the following?

I. the use of test-tube experimentation alone to establish the validity of scientific theories
II. the exclusion of experimental facts from the formation of scientific theories
III. the observation of certain cellular components in isolation

A) I only
B) I and II only
C) I and III only
D) II and III only
E) I, II and III

Type: Detail of the passage

(E) The last sentence of the third paragraph shows that the author is against the use of test-tube experimentation alone to establish the validity of scientific theories. The last paragraph also tells us that the author is against options II and III. Hence, (E) is the correct answer. This question requires a scanning of the entire passage. I and II deal with our author’s crusade of experimentation versus dogma. III is our author’s concern with complexity versus simple isolation.

4. The author refers to the results of test-tube experiments involving the replication of DNA primarily in order to

A) question the validity of experimental results that describe the structure of DNA.
B) provide evidence to contradict the theory that DNA alone governs protein synthesis.
C) show the way in which DNA acts as a self-duplicating molecule.
D) explain the internal structure of DNA.
E) reveal how nucleic acid can influence the synthesis of proteins.

Type: Function of a part of the passage

(B) In the second paragraph, the author says that there was “an admittedly unproven assumption that, whereas nucleic acids can guide the synthesis in other nucleic acids and of proteins, the reverse effect is impossible. However, actual experimental observations deny the second and crucial part of this assumption.” Other test-tube experiments show that agents besides DNA have a guiding influence. The answer relates to experiment vs. established dogma. The answer is directly available from the second paragraph but requires an understanding of the context.

5. According to the passage, a metal cannot become super conductive unless:

A) the voltage through the metal is increased.
B) the metal’s atomic structure has been destroyed.
C) the metal is exposed to very low temperatures.
D) electrons in the metal interact with one another at ordinary temperatures.
E) electrical flow is provided by a battery.

Type: Detail of the passage

(C) The third sentence of the fourth paragraph states that “At temperatures near absolute zero, metals exhibit superconductivity: a unique property that causes an electric current to flow for months after the voltage is cut off.” This question is just a fact check from the essay and doesn’t test any real understanding.

6. The author suggests that the most important difference observed between a dead cell and a living cell results primarily from the

A) differences in the chemical elements present in each.
B) differences in the degree of acidity present in each.
C) biochemical procedures used to examine each cell.
D) varying temperatures at which cells are examined.
E) integrating mechanism thought to exist within the structure of the living cell.

Type: Detail of the passage

(E) The last two sentences of the third paragraph state “No matter how many ingredients the biochemists’ test tubes may contain, the mixtures are nonliving. However, these same ingredients, organized by the subtle structure of the cell, constitute a system, which is alive.” Again, this ties into the author’s theme of complexity.

7. The experimental results mentioned in the passage suggest that biological inheritance depends on:

A) instructions contained in a single molecule within the cell.
B) processes that are guided by specific enzymes.
C) genetic information contained in metallic salts.
D) interactions among several molecular processes in the cell.
E) replicative processes within the chemistry of protein synthesis.

Type: Detail of the passage

(D) The second sentence in the third paragraph states, “In the living cell, molecular processes – the synthesis of nucleic acids and proteins or the oxidation of food substance – are not separate but interact in exceedingly complex ways.” You didn’t even have to look this up, though, because if you clearly understood the author’s thinking, it would be easy. The answer is directly available and needs no inference.

8. The author presents his argument primarily by:

A) contrasting two fields of science.
B) providing experimental evidence against a point of view.
C) criticizing proponents of other theories.
D) stating a new theory and its important implications.
E) comparing two theories of cellular structure.

Type: Organization of the passage

(B) This question is asking you to remember the author’s main point and then explain how he or she makes it. (B) states just this: the experiments the author refers to and their refuting of the “dogma.” (D) may have tricked you since the author is discussing his theory, but this essay is railing against an established point of view and not an introduction of a new theory.

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