Q: Which equation correctly represents the process of aerobic respiration that contributes to BOD?

$$\mathrm{C_6H_{12}O_6$} + 6\ \mathrm{O_2$} \rightarrow 6\ \mathrm{CO_2$} + 6\ \mathrm{H_2O} + \text{Energy}$$

Question 1

Which of the following best defines biochemical oxygen demand (BOD)?

Accepted Answer

The amount of O$$_2$$ removed from the environment by microbial respiration.

Question 2

A river receives runoff containing high levels of NH$$_4^+$$, NO$$_3^-$$, and PO$$_4$$^{3-}$$. What is the most likely sequence of events that will occur in the river ecosystem?

Accepted Answer

Algal bloom, followed by death of algae, then increased heterotrophic bacterial activity and oxygen depletion.

Question 3

Which equation correctly represents the process of aerobic respiration that contributes to BOD?

Accepted Answer

$$\mathrm{C_6H_{12}O_6$} + 6\ \mathrm{O_2$} ightarrow 6\ \mathrm{CO_2$} + 6\ \mathrm{H_2O} + 	ext{Energy}$$

Question 4

Why do hypoxic zones, or 'dead zones,' form in regions such as the Gulf of Mexico?

Accepted Answer

Aerobic respiration by heterotrophic bacteria depletes oxygen after algal blooms die off.

Question 5

Which stage of wastewater treatment primarily involves microbial decomposition of organic content?

Accepted Answer

Secondary treatment

Question 6

What is the main purpose of floc formation in the activated sludge process during wastewater treatment?

Accepted Answer

To promote settling of bacteria and associated microbes for removal from the effluent.

Question 7

Which of the following best describes the 'nitrogen triangle' in the nitrogen cycle?

Accepted Answer

Nitrogen fixation, nitrification, and denitrification.

Question 8

Which process in the nitrogen cycle is responsible for converting atmospheric N$$_2$$ into ammonia (NH$$_3) $$usable by living organisms?

Accepted Answer

Nitrogen fixation

Question 9

What is the environmental consequence of excessive fertilizer use leading to nitrate (NO$$_3^-) $$runoff?

Accepted Answer

Eutrophication and potential formation of hypoxic zones.

Question 10

During denitrification, which of the following is the correct sequence of nitrogen compounds produced as nitrate (NO$$_3^-) is $$reduced?

Accepted Answer

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

Question 11

A sample of river water is tested for dissolved oxygen over time. Which sample has the highest BOD?

Accepted Answer

The sample with the fastest decrease in dissolved oxygen.

Question 12

Which of the following is a direct result of aerobic respiration by heterotrophic bacteria in aquatic environments?

Accepted Answer

Decrease in dissolved oxygen levels, contributing to BOD.

Question 13

Which of the following best explains why nitrogen cycling cannot occur without prokaryotes?

Accepted Answer

Only prokaryotes possess the enzymes required for nitrogen fixation and nitrification.

Question 14

Which of the following is a potential negative impact of denitrification in hypoxic aquatic environments?

Accepted Answer

Release of nitrous oxide (N$$_2O$$), a potent greenhouse gas.

Question 15

Which of the following is a key factor that promotes effective wastewater treatment?

Accepted Answer

Proper floc formation to facilitate settling of microbes.

Question 16

A municipal wastewater treatment plant is experiencing poor effluent quality. Microscopic analysis reveals a low ratio of filamentous to planktonic bacteria in the activated sludge. What is the most likely consequence?

Accepted Answer

Poor floc formation, leading to reduced removal of bacteria from the effluent.

Question 17

Which of the following best describes the role of symbiotic nitrogen-fixing bacteria in the nitrogen cycle?

Accepted Answer

They convert atmospheric N$$_2$$ into ammonia for use by their plant hosts.

Question 18

Which of the following chemical equations represents the industrial Haber process for nitrogen fixation?

Accepted Answer

$$\mathrm{N_2$} + 3\ \mathrm{H_2$} \rightarrow 2\ \mathrm{NH_3$}$$

Question 19

Which of the following is a real-world consequence of high BOD in a river receiving untreated sewage?

Accepted Answer

Depletion of dissolved oxygen, leading to fish and invertebrate die-offs.

Question 20

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

Accepted Answer

Oxidation of ammonia (NH$$_4^+) to $$nitrite (NO$$_2^-) $$and then to nitrate (NO$$_3^-) by $$soil bacteria.

Environmental Microbiology: Hydrologic Cycle, Biochemical Oxygen Demand, Eutrophication, Dead Zones, and Wastewater Treatment

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