630 Microbiology for Teachers

Sample Questions for Exam 4 (July 12)

MULTIPLE CHOICE: Circle the letter corresponding to the one true answer for each question.

1. Which statement about the biogeochemical cycles is true?
   1. Due to their metabolic flexibility, microbial lithotrophs and phototrophs act as consumers more often than they act as primary producers.
   2. The carbon, nitrogen and sulfur cycles, but not the iron cycle, can all be completed in both anaerobic and aerobic environments.
   3. Organotrophic microbes often act as decomposers in the carbon cycle, but play no role in either the sulfur or the nitrogen cycles.
2. Which statement about environmental nitrogen metabolism is true?
   1. The reactions involved in nitrogen fixation are oxidative and require ATP; thus they require an aerobic environment if they are to be carried out efficiently.
   2. During nitrogen-fixation, one N2 molecule is converted to two NH3 molecules in three steps by an enzyme complex that contains dinitrogenase.
   3. Dissimilative nitrogen reactions are those through which reduced forms of nitrogen are incorporated into organic compounds such as amino acids.

MATCHING MULTIPLE CHOICE: Write the letter corresponding to the BEST answer in the blank. You may need to use an answer more than once within the set of questions indicated.

Answers to questions 3-4:

1. anoxygenic phototrophs
2. anaerobic organotrophs
3. aerobic organotrophs
4. oxygenic phototrophs
5. aerobic lithotrophs

3. Bacteria involved in the carbon cycle because they produce cellulase, and are therefore able to partially degrade the glucose storage molecule cellulose, are most likely to be _____.
4. Bacteria that are active in the sulfur cycle because they carry out the reaction sequence H₂S S under anaerobic conditions, are most likely to be _____.

TRUE-FALSE: If a statement is TRUE, write T in the blank provided; if it is FALSE, write F in the blank.

5. _____ Soil is formed by a combination of physical, chemical and biological processes by which parent material is fragmented into successively smaller particles to form material that is generally wet, anaerobic (but with aerobic microsites) and eutrophic, is composed of both organic and inorganic components, and contains a mixture of microorganisms.
6. _____ One example of syntrophy is an interaction between two separate species of microbes that allows one of them to carry out an energetically unfavorable fermentation by providing H₂ to neighboring microbes, which use it in energetically very favorable reactions.

Essay Question: Write your answer in the space provided.

7. (5 pt) The newly-opened LazeDaze Clothes Washing Emporium, which uses large amounts of phosphate-containing detergents, dumps the water that has been used for washing clothes into a small pond behind the establishment. As a result, the pond has become completely clogged with cyanobacteria such as Anabaena, Nostoc, and Cylindrospermum. Discuss why this nitrogen-poor pond is supporting these cyanobacteria and not green algae, being certain to explain how this condition is initiated and how it might be maintained.