Question 1

Which of the following best describes the process of methanogenesis in the carbon cycle?

Accepted Answer

The reduction of carbon dioxide to methane by archaea under anaerobic conditions.

Question 2

Which equation correctly represents the process of nitrification in the nitrogen cycle?

Accepted Answer

$$\mathrm{NH_4$^+ + 2\ O_2$ \rightarrow NO_3$^- + 2\ H^+ + H_2O}$$

Question 3

A wastewater treatment plant is experiencing a buildup of ammonia ($$\mathrm{NH_3$}). $$Which microbial process is most likely failing?

Accepted Answer

Nitrification

Question 4

Which of the following is a significant impact of human activity on the nitrogen cycle?

Accepted Answer

Eutrophication of aquatic systems due to fertilizer runoff.

Question 5

Which of the following best describes the role of syntrophy in methanogenesis?

Accepted Answer

Syntrophic bacteria oxidize substrates to produce hydrogen, which methanogens use to reduce carbon dioxide to methane.

Question 6

Which of the following equations represents the process of denitrification?

Accepted Answer

$$\mathrm{NO_3$^- \rightarrow NO_2$^- \rightarrow NO \rightarrow N_2O \rightarrow N_2$}$$

Question 7

Which form of mercury is most toxic to humans and why?

Accepted Answer

Methylmercury ($$\mathrm{CH_3Hg^+}) $$because it bioaccumulates in food chains.

Question 8

How do bacteria resist the toxic effects of mercury in the environment?

Accepted Answer

By converting methylmercury to elemental mercury ($$\mathrm{Hg^0$}$$), which is less toxic and volatile.

Question 9

Which process in the sulfur cycle is carried out by sulfur-oxidizing bacteria?

Accepted Answer

Oxidation of hydrogen sulfide to sulfate.

Question 10

A farmer applies large amounts of nitrogen fertilizer to his fields. Which of the following is a likely environmental consequence?

Accepted Answer

Eutrophication of nearby lakes due to runoff of excess nitrate.

Question 11

Which of the following best describes the process of ammonification?

Accepted Answer

Decomposition of organic nitrogen compounds to ammonia.

Question 12

Which of the following equations represents the anammox process?

Accepted Answer

$$\mathrm{NH_4$^+ + NO_2$^- \rightarrow N_2$ + 2\ H_2O}$$

Question 13

Which of the following is a direct effect of increased atmospheric carbon dioxide due to human activity?

Accepted Answer

Ocean acidification due to increased dissolution of $$\mathrm{CO_2$}.$$

Question 14

Which of the following best describes the movement of sulfur through ecosystems?

Accepted Answer

Sulfur moves between organic and inorganic forms through microbial oxidation and reduction.

Question 15

Which of the following is a real-world example of how humans are exposed to mercury?

Accepted Answer

Consumption of fish contaminated with methylmercury.

Question 16

Which process is responsible for the conversion of atmospheric nitrogen ($$\mathrm{N_2$}) $$into a biologically usable form?

Accepted Answer

Nitrogen fixation

Question 17

A lake near a coal-burning power plant has elevated levels of sulfate. Which microbial process is likely to increase in the lake sediments?

Accepted Answer

Sulfate reduction

Question 18

Which of the following is an example of an organic sulfur compound?

Accepted Answer

Dimethyl sulfide ($$\mathrm{(CH_3$)_2S})$$

Question 19

Which of the following best explains why methylmercury is more dangerous than elemental mercury?

Accepted Answer

Methylmercury bioaccumulates in organisms and magnifies up the food chain.

Question 20

Which of the following is a key role of decomposition in the carbon cycle?

Accepted Answer

Release of carbon dioxide back into the atmosphere from organic matter.

Nutrient Cycles in Microbial Ecosystems

Study Guide - Practice Questions