They normally lack chlorophyll.
25. It can be inferred from the passage that cell differentiation within Anabaena is regulated by the
amount of oxygen Anabaena cells produce
season of the year
amount of fixed nitrogen compounds available
number of microscopic channels uniting Anabaena cells
amount of chlorophyll in Anabaena cells
26. The passage supports which of the following inferences about heterocysts?
Heterocysts do not produce oxygen.
Nitrogen gas inactivates heterocysts.
Chlorophyll increases the productivity of heterocysts.
Heterocysts allow nitrogen fixation and photosynthesis to occur in the same cell.
Heterocysts are more important for Anabaenas functioning than are photosynthetic cells.
27. The author uses the example of Anabaena to illustrate the
uniqueness of bacteria among unicellular organisms
inadequacy of an existing view of bacteria
ability of unicellular organisms to engage in photosynthesis
variability of a freshwater bacteria
difficulty of investigating even the simplest unicellular organisms
答案:17-27:CBEBCDDBCAB
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