This first essay is previously used in the chapter. You may choose to skip over it.
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.
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.
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.
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.
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.
1. The author is primarily 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.
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
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
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.
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.
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.
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.
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.
Play by Play
PARAGRAPH 1
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. |
PARAGRAPH 2
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. |
PARAGRAPH 3
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 begins to really 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. |
|
|
|
PARAGRAPH 4
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.
|
|
|
|
PARAGRAPH 5
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.
|
|
|
|
1.
What is the passage type?
Subject: Science
Action: Persuade
2. What
is each paragraph about?
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?
This is a theory / counter-theory passage.
| Old Theory: |
|
Protein
synthesis is a simple matter of DNA |
 |
|
|
| Problem with theory: |
|
Other agents influence protein synthesis |
|
|
|
| Implication of problem: |
|
Cells are complicated,
coordinated systems |
|
|
|
| Explanatory analogy: |
|
Example of superconductivity metals |
|
|
|
| Summary: |
|
Cells are complicated, coordinated systems |
| |
|
|
4. What is the big idea?
Cells are so complex
that the current theory doesn't do them justice.
5
. What is the author's purpose?
The author takes issue with an old theory about cells and introduces a new theory as an alternative.
Explanations
1. The author is primarily 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. (difficulty level 500 on a scale from 200 to 800)
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. (difficulty level 300 on a scale from 200 to 800).
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.
(difficulty level 400 on a scale from 200 to 800)
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 last three sentences of 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. (difficulty level 300 on a scale from 200 to 800)
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. (difficulty level 200 on a scale from 200 to 800)
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 line of the third paragraph illustrates that "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. (difficulty level 300 on a scale from 200 to 800)
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. (difficulty level 300 on a scale from 200 to 800)
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.
(difficulty level 500 on a scale from 200 to 800)
|
