Question 1

Which of the following best describes a redox reaction in the context of bacterial metabolism?

Accepted Answer

A reaction where both oxidation and reduction occur simultaneously, allowing the transfer of electrons between molecules.

Question 2

Which equation correctly represents the reduction of nitrate ($$\mathrm{NO_3$^-}) to $$nitrite ($$\mathrm{NO_2$^-}) $$during anaerobic respiration?

Accepted Answer

$$\mathrm{NO_3$^-} + 2e^- + 2H^+ \rightarrow \mathrm{NO_2$^-} + H_2O$$

Question 3

Which of the following statements best distinguishes assimilative from dissimilative metabolism?

Accepted Answer

Assimilative metabolism incorporates nutrients into biomass, while dissimilative metabolism uses nutrients as electron acceptors for energy production.

Question 4

A chemolithotrophic bacterium oxidizes ammonia ($$\mathrm{NH_3$}) to $$nitrite ($$\mathrm{NO_2$^-}) $$for energy. Which process is this an example of?

Accepted Answer

Nitrification

Question 5

Which of the following is a key feature of the Calvin cycle in autotrophic bacteria?

Accepted Answer

It fixes carbon dioxide ($$\mathrm{CO_2$}) $$into organic molecules using the enzyme RuBisCO.

Question 6

Which pathway is used by some autotrophic bacteria to fix carbon and is essentially the reverse of the citric acid cycle?

Accepted Answer

Reverse Citric Acid Cycle

Question 7

A bacterium uses hydrogen sulfide ($$\mathrm{H_2S}) as an $$electron donor and oxygen as an electron acceptor. What type of metabolism is this?

Accepted Answer

Chemolithotrophy

Question 8

Which of the following best describes the reductive acetyl-CoA pathway?

Accepted Answer

A carbon fixation pathway that reduces $$\mathrm{CO_2$} to $$form acetyl-CoA, used by some anaerobic bacteria and archaea.

Question 9

During anaerobic respiration, which of the following can serve as a terminal electron acceptor?

Accepted Answer

Sulfate ($$\mathrm{SO_4$^{2-}})$$

Question 10

A bacterium is found to reduce $$\mathrm{Fe$$^{3+}$$} to$$ $$\mathrm{Fe$$^{2+}$$}$$ during growth in anoxic sediments. This process is best described as:

Accepted Answer

Dissimilative metal reduction

Question 11

Which of the following equations represents the oxidation of ammonia ($$\mathrm{NH_3$}) to $$nitrite ($$\mathrm{NO_2$^-}) by $$chemolithotrophic bacteria?

Accepted Answer

$$\mathrm{NH_3$} + 1.5\,\mathrm{O_2$} \rightarrow \mathrm{NO_2$^-} + \mathrm{H_2O} + 2H^+$$

Question 12

Which of the following is NOT a typical electron acceptor used in anaerobic respiration by bacteria?

Accepted Answer

Glucose

Question 13

A bacterium is isolated from a contaminated aquifer and is found to use trichloroethylene (a halogenated molecule) as an electron acceptor. This process is best described as:

Accepted Answer

Anaerobic respiration using halogenated molecules as electron acceptors

Question 14

Which of the following best explains why chemolithotrophic bacteria are important in the nitrogen cycle?

Accepted Answer

They oxidize ammonia to nitrite and nitrite to nitrate, facilitating nitrogen transformations in the environment.

Question 15

Which of the following is a multi-step process involving both oxidation and reduction reactions, and is essential for energy generation in many bacteria?

Accepted Answer

Respiratory electron transport chain

Question 16

A bacterium is capable of using both $$\mathrm{NO_3$^-}$$ and $$\mathrm{SO_4$^{2-}} as $$terminal electron acceptors depending on environmental conditions. What does this metabolic flexibility indicate?

Accepted Answer

The bacterium can perform different types of anaerobic respiration based on electron acceptor availability.

Question 17

Which of the following is a real-world application of bacteria that use the reductive acetyl-CoA pathway?

Accepted Answer

Production of acetate from $$\mathrm{CO_2$} in $$anaerobic digesters for biofuel generation.

Question 18

Which of the following best describes the role of RuBisCO in the Calvin cycle?

Accepted Answer

It catalyzes the fixation of $$\mathrm{CO_2$} to $$ribulose-1,5-bisphosphate.

Question 19

A bacterium is found to use $$\mathrm{SO_4$^{2-}} as a $$terminal electron acceptor, reducing it to $$\mathrm{H_2S}. $$Which equation best represents this process?

Accepted Answer

$$\mathrm{SO_4$^{2-}} + 8e^- + 8H^+ \rightarrow \mathrm{H_2S} + 4H_2O$$

Question 20

Which of the following scenarios best illustrates dissimilative nitrate reduction?

Accepted Answer

A bacterium reduces nitrate to nitrogen gas for energy production, releasing the nitrogen gas into the environment.

Metabolic Diversity of Microorganisms: Redox, Autotrophy, and Respiratory Processes

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