Question 1

Which of the following statements best explains why anaerobic respiration yields less energy than aerobic respiration?

Accepted Answer

Anaerobic respiration uses electron acceptors with lower reduction potentials than oxygen, resulting in less energy released per electron transferred. $$\Delta G = -nF\Delta E^\circ'$$

Question 2

During the fermentation process used to make pickles (as shown in the image), which of the following statements is correct?

Accepted Answer

Fermentation occurs in the absence of external electron acceptors, and ATP is generated by substrate-level phosphorylation.

Question 3

Which of the following is NOT a possible terminal electron acceptor in anaerobic respiration?

Accepted Answer

Oxygen ($$O_2)$$

Question 4

A bacterium is classified as a chemoorganoheterotroph. Which of the following best describes its sources of energy, electrons, and carbon?

Accepted Answer

Energy from chemicals, electrons from organic compounds, carbon from organic compounds.

Question 5

Which of the following best describes the role of the Calvin cycle in autotrophic microorganisms?

Accepted Answer

It fixes $$CO_2$$ into organic molecules using ATP and NADPH.

Question 6

Which enzyme is directly responsible for catalyzing the fixation of $$CO_2 in $$the Calvin cycle?

Accepted Answer

Ribulose bisphosphate carboxylase/oxygenase (RuBisCO)

Question 7

Nitrogen fixation is a process carried out by certain prokaryotes. Which of the following statements is TRUE regarding nitrogen fixation?

Accepted Answer

It is catalyzed by nitrogenase, which is sensitive to oxygen.

Question 8

In the process of nitrification, which sequence of chemical transformations occurs?

Accepted Answer

Ammonia ($$NH_3) is $$oxidized to nitrite ($$NO_2$$^-$$), then nitrite is oxidized to nitrate (NO_3$^-).$$

Question 9

Which of the following best explains why the growth of nitrifying bacteria is typically slow?

Accepted Answer

The energy yield from the oxidation of ammonia and nitrite is very small.

Question 10

Which of the following is a key difference between oxygenic and anoxygenic photosynthesis?

Accepted Answer

Oxygenic photosynthesis uses water as an electron donor and produces $$O_2$$; anoxygenic photosynthesis does not.

Question 11

Which of the following best describes the function of the proton motive force (pmf) in microbial metabolism?

Accepted Answer

It drives ATP synthesis via ATPase by utilizing the electrochemical gradient across the membrane.

Question 12

Which of the following is a correct example of a syntrophic relationship?

Accepted Answer

One microbe produces hydrogen ($$H_2) as a $$fermentation product, which is immediately consumed by a methanogen.

Question 13

Which of the following equations represents the overall stoichiometry of the Calvin cycle for the synthesis of one molecule of glucose?

Accepted Answer

$$6CO_2 + 12NADPH + 18ATP \rightarrow C_6H_{12}O_6$ + 12NADP^+ + 18ADP + 18P_i$$

Question 14

Which of the following is a correct statement about denitrification?

Accepted Answer

It is the reduction of nitrate ($$NO_3$$^-$$) to nitrogen gas (N_2$) under anaerobic conditions.

Question 15

A microorganism is capable of using light as an energy source, inorganic compounds as electron donors, and $$CO_2 as a $$carbon source. How would you classify this organism?

Accepted Answer

Photolithoautotroph

Question 16

Which of the following is a correct description of methanogenesis?

Accepted Answer

It is a process in which certain archaea produce methane ($$CH_4) $$from $$CO_2$$ and $$H_2.$$

Question 17

Which of the following best explains why nitrogenase is sensitive to oxygen?

Accepted Answer

Oxygen irreversibly inactivates the nitrogenase enzyme complex.

Question 18

Which of the following is a correct sequence of electron flow in oxygenic photosynthesis?

Accepted Answer

Water $$\rightarrow$$ Photosystem II $$\rightarrow$$ Photosystem I $$\rightarrow$$ NADP$$^+$$

Question 19

Which of the following is a major ecological consequence of denitrification in soil?

Accepted Answer

Loss of bioavailable nitrogen as $$N_2$$ gas, reducing soil fertility.

L5 Microbial Metabolism: Catabolic Diversity and Energy Conservation

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