Question 1

Which of the following best describes the role of mycorrhizae in plant growth, as demonstrated by the basil plants in the provided image?

Accepted Answer

Mycorrhizae form a mutualistic relationship with plant roots, increasing surface area for nutrient and water absorption, thereby enhancing plant growth.

Question 2

Which process in the nitrogen cycle is responsible for converting ammonium ions ($$NH_4$$^+$$) into nitrate ions (NO_3$^-$$), and which bacteria are primarily involved?

Accepted Answer

Nitrification; Nitrosomonas and Nitrobacter

Question 3

In the context of biogeochemical cycles, what is the primary role of decomposers in the carbon cycle?

Accepted Answer

They oxidize organic compounds from dead plants and animals, releasing $$CO_2$$ back into the atmosphere.

Question 4

Which of the following best explains why eutrophication leads to fish kills in lakes and streams?

Accepted Answer

Excess nitrogen and phosphorus cause algal blooms, and the subsequent bacterial degradation of dead algae depletes dissolved oxygen.

Question 5

Which of the following is a limitation of using coliforms as indicator organisms for water purity tests?

Accepted Answer

Viruses and protozoans such as Giardia and Cryptosporidium can be present even when coliforms are absent.

Question 6

Which process is enhanced by the addition of nitrogen and phosphorus fertilizers after an oil spill, as shown in the image of the Exxon Valdez cleanup?

Accepted Answer

Bioremediation

Question 7

What is the main function of the activated sludge system in secondary sewage treatment?

Accepted Answer

To use aerobic microbes to oxidize organic matter, removing 75–95% of biochemical oxygen demand (BOD).

Question 8

Which of the following best describes the process of denitrification in the nitrogen cycle?

Accepted Answer

Conversion of nitrate ($$NO_3$$^-$$) to nitrogen gas (N_2$) by bacteria in the absence of oxygen.

Question 9

Which of the following is a real-world example of bioaugmentation?

Accepted Answer

Adding specific oil-degrading bacteria to a contaminated beach after an oil spill.

Question 10

Which enzyme is essential for the process of biological nitrogen fixation?

Accepted Answer

Nitrogenase

Question 11

Which of the following best explains why most soil bacteria cannot be cultured in the laboratory?

Accepted Answer

They require specific nutrients and environmental conditions not easily replicated in the lab.

Question 12

Which of the following is a key difference between endomycorrhizae and ectomycorrhizae?

Accepted Answer

Endomycorrhizae penetrate plant root cells, while ectomycorrhizae form a sheath around the root surface.

Question 13

Which of the following best describes the process of ammonification in the nitrogen cycle?

Accepted Answer

Release of ammonia ($$NH_3) $$from the decomposition of organic matter by bacteria and fungi.

Question 14

Which of the following is a major environmental concern associated with the use of synthetic chemicals known as xenobiotics?

Accepted Answer

They are resistant to microbial degradation and persist in the environment.

Question 15

Which of the following steps in municipal water treatment is specifically designed to remove colloidal materials, bacteria, and viruses?

Accepted Answer

Flocculation

Question 16

A farmer wants to improve the nitrogen content of his soil without using synthetic fertilizers. Which microbial process and organisms should he encourage in his fields?

Accepted Answer

Nitrogen fixation by free-living bacteria such as Azotobacter and symbiotic bacteria such as Rhizobium.

Question 17

Which of the following best describes the function of heterocysts in cyanobacteria?

Accepted Answer

They provide anaerobic conditions necessary for nitrogen fixation.

Question 18

Which of the following is a primary goal of tertiary sewage treatment ('toilet to tap')?

Accepted Answer

Removal of remaining BOD, nitrogen, and phosphorus to produce drinkable water.

Question 19

Which of the following best explains why burning fossil fuels contributes to global warming in the context of the carbon cycle?

Accepted Answer

It releases stored $$CO_2$$ into the atmosphere, increasing greenhouse gas concentrations.

Question 20

Which of the following is a real-world application of composting in waste management?

Accepted Answer

Converting municipal organic waste into humus by promoting microbial degradation by thermophiles.

Environmental Microbiology: Microbial Diversity, Biogeochemical Cycles, and Water Treatment

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