6. Which of the following microorganism use H2S as the electron donor to reduce carbon dioxide?
A. Chromatium
B. Chlorobium
C. Both (a) and (b)
D. Rhodomicrobium
7. Nitrifying bacteria can not be isolated directly by the usual techniques employed to isolate heterotrophic bacteria. The reasons may be due to
A. slow growth
B. medium growth
C. fast growth
D. none of these
8. Bacteria, as a group, are responsible for
A. nitrogen oxidation
B. sulfur oxidation
C. nitrogen fixation
D. all of these
9. The phenomenon of commensalism refers to a relationship between organisms in which
A. one species of a pair benefits
B. both the species of a pair benefit
C. one species of a pair is more benefited
D. none of the above
10. The population of algae in the soil is __________ that of either bacteria or fungi.
A. generally smaller than
B. generally greater than
C. equal to
D. none of these