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Researchers are finding that in many ways an individual bact
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10 Mar 2020, 09:53
10 Mar 2020, 09:53
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Researchers are finding that in many ways an individual bacterium is more analogous to a component cell of a multicellular organism than it is to a free-living, autonomous organism. Anabaena, a freshwater bacteria, is a case in point. Among photosynthetic bacteria, Anabaena is unusual: it is capable of both photosynthesis and nitrogen fixation. Within a single cell, these two biochemical processes are incompatible: oxygen, produced during photosynthesis, inactivates the nitrogenase required for nitrogen fixation. In Anabaena communities, however, these processes can coexist. When fixed nitrogen compounds are abundant, Anabaena is strictly photosynthetic and its cells are all alike. When nitrogen levels are low, however, specialized cells called heterocysts are produced which lack chlorophyll (necessary for photosynthesis) but which can fix nitrogen by converting nitrogen gas into a usable form. Submicroscopic channels develop which connect the heterocyst cells with the photosynthetic ones and which are used for transferring cellular products between the two kinds of Anabaena cells.
Question 1
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Question Stats:
75% (02:22) correct
25% (03:10) wrong based on 61 sessions
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24. According to the passage, which of the following statements is true of bacteria that engage in photosynthesis?
(A) They eventually become two autonomous cells.
(B) They cannot normally also engage in nitrogen fixation.
(C) Oxygen normally inactivates them.
(D) Cellular products are constantly transferred between such bacteria.
(E) They normally lack chlorophyll.
Question 2
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Question Stats:
73% (00:47) correct
27% (01:02) wrong based on 55 sessions
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25. It can be inferred from the passage that cell differentiation within Anabaena is regulated by the
(A) amount of oxygen Anabaena cells produce
(B) season of the year
(C) amount of fixed nitrogen compounds available
(D) number of microscopic channels uniting Anabaena cells
(E) amount of chlorophyll in Anabaena cells
Question 3
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50% (01:04) correct
50% (01:18) wrong based on 46 sessions
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26. The passage supports which of the following inferences about heterocysts?
(A) Heterocysts do not produce oxygen.
(B) Nitrogen gas inactivates heterocysts.
(C) Chlorophyll increases the productivity of heterocysts.
(D) Heterocysts allow nitrogen fixation and photosynthesis to occur in the same cell.
(E) Heterocysts are more important for Anabaena's functioning than are photosynthetic cells.
Question 4
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Question Stats:
29% (00:47) correct
71% (00:58) wrong based on 48 sessions
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27. The author uses the example of Anabaena to illustrate the
(A) the uniqueness of bacteria among unicellular organisms
(B) inadequacy of an existing view of bacteria
(C) ability of unicellular organisms to. engage in photosynthesis
(D) variability of a freshwater bacteria
(E) the difficulty of investigating even the simplest unicellular organisms
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Re: Researchers are finding that in many ways an individual bact
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11 Apr 2020, 01:46
11 Apr 2020, 01:46
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24. According to the passage, which of the following statements is true of bacteria that engage in photosynthesis?
(A) They eventually become two autonomous cells.
(B) They cannot normally also engage in nitrogen fixation.
(C) Oxygen normally inactivates them.
(D) Cellular products are constantly transferred between such bacteria.
(E) They normally lack chlorophyll.
"Anabaena is unusual: it is capable of both photosynthesis and nitrogen fixation." This suggests that it is unique among all the bacteria because it can perform photosynthesis and nitrogen fixation at the same time.
25. It can be inferred from the passage that cell differentiation within Anabaena is regulated by the
(A) amount of oxygen Anabaena cells produce
(B) season of the year
(C) amount of fixed nitrogen compounds available
(D) number of microscopic channels uniting Anabaena cells
(E) amount of chlorophyll in Anabaena cells
Cell differentiation is regulated by the amount of nitrogen available in the cell. Because, when it is abundant cells can perform photosynthesis,, but when they are not then special cells can be produced to do nitrogen fixation.
26. The passage supports which of the following inferences about heterocysts?
(A) Heterocysts do not produce oxygen.
(B) Nitrogen gas inactivates heterocysts.
(C) Chlorophyll increases the productivity of heterocysts.
(D) Heterocysts allow nitrogen fixation and photosynthesis to occur in the same cell.
(E) Heterocysts are more important for Anabaena's functioning than are photosynthetic cells.
The passage says that oxygen is produced during photosynthesis, so if heterocysts lack chlorophyll that is necessary for photosynthesis, then option A can be inferred.
27. The author uses the example of Anabaena to illustrate the
(A) the uniqueness of bacteria among unicellular organisms
(B) inadequacy of an existing view of bacteria
(C) ability of unicellular organisms to. engage in photosynthesis
(D) variability of a freshwater bacteria
(E) the difficulty of investigating even the simplest unicellular organisms
Anabaena is unique for sure but the passage is not written to highlight this point and it is unique among "photosynthetic bacteria". The author started the passage with saying that "Researchers are finding that an individual bacterium is more analogous to a component cell of a multicellular organism than it is to a free-living". This means that the existing view is lacking this concept.
Having option A&B together in the same question, the GRE is trying to vex the test takers.
However, the rest of the choices are far from being close to the correct answer.
(A) They eventually become two autonomous cells.
(B) They cannot normally also engage in nitrogen fixation.
(C) Oxygen normally inactivates them.
(D) Cellular products are constantly transferred between such bacteria.
(E) They normally lack chlorophyll.
"Anabaena is unusual: it is capable of both photosynthesis and nitrogen fixation." This suggests that it is unique among all the bacteria because it can perform photosynthesis and nitrogen fixation at the same time.
25. It can be inferred from the passage that cell differentiation within Anabaena is regulated by the
(A) amount of oxygen Anabaena cells produce
(B) season of the year
(C) amount of fixed nitrogen compounds available
(D) number of microscopic channels uniting Anabaena cells
(E) amount of chlorophyll in Anabaena cells
Cell differentiation is regulated by the amount of nitrogen available in the cell. Because, when it is abundant cells can perform photosynthesis,, but when they are not then special cells can be produced to do nitrogen fixation.
26. The passage supports which of the following inferences about heterocysts?
(A) Heterocysts do not produce oxygen.
(B) Nitrogen gas inactivates heterocysts.
(C) Chlorophyll increases the productivity of heterocysts.
(D) Heterocysts allow nitrogen fixation and photosynthesis to occur in the same cell.
(E) Heterocysts are more important for Anabaena's functioning than are photosynthetic cells.
The passage says that oxygen is produced during photosynthesis, so if heterocysts lack chlorophyll that is necessary for photosynthesis, then option A can be inferred.
27. The author uses the example of Anabaena to illustrate the
(A) the uniqueness of bacteria among unicellular organisms
(B) inadequacy of an existing view of bacteria
(C) ability of unicellular organisms to. engage in photosynthesis
(D) variability of a freshwater bacteria
(E) the difficulty of investigating even the simplest unicellular organisms
Anabaena is unique for sure but the passage is not written to highlight this point and it is unique among "photosynthetic bacteria". The author started the passage with saying that "Researchers are finding that an individual bacterium is more analogous to a component cell of a multicellular organism than it is to a free-living". This means that the existing view is lacking this concept.
Having option A&B together in the same question, the GRE is trying to vex the test takers.
However, the rest of the choices are far from being close to the correct answer.
General Discussion
Re: Researchers are finding that in many ways an individual bact
[#permalink]
10 Apr 2020, 16:29
10 Apr 2020, 16:29
1
Hi, could you provide an explanation (particularly for questions 25-27), thank you!
