Question 1

Which of the following statements best explains why aerobic respiration yields more energy than anaerobic respiration in microorganisms?

Accepted Answer

Aerobic respiration uses O$$_2 as $$the terminal electron acceptor, which has the highest reduction potential, allowing for the greatest energy release during electron transport.

Question 2

A chemolithotrophic bacterium oxidizes H$$_2S to SO$_4$$^{2-}$$ using O_2$ as the electron acceptor. Which process is this organism performing?

Accepted Answer

Aerobic sulfur oxidation

Question 3

Which of the following is a key enzyme in the Calvin cycle responsible for CO$$_2$$ fixation?

Accepted Answer

RubisCO

Question 4

In the process of electron bifurcation, what is the main advantage for fermentative microorganisms?

Accepted Answer

It allows the endergonic reduction of low-potential electron acceptors by coupling to exergonic reactions, increasing energy yield and redox balance.

Question 5

Which of the following best describes the function of carboxysomes in autotrophic bacteria?

Accepted Answer

They compartmentalize RubisCO, protecting it from O$$_2$$ and enhancing CO$$_2$$ fixation efficiency.

Question 6

A bacterium is found to grow in deep, anoxic sediments using Fe$$^{3+} as an $$electron acceptor and acetate as an electron donor. Which process is most likely occurring?

Accepted Answer

Dissimilative iron reduction

Question 7

Which of the following is a distinguishing feature of anoxygenic photosynthesis compared to oxygenic photosynthesis?

Accepted Answer

Anoxygenic photosynthesis uses electron donors other than H$$_2O $$and does not produce O$$_2 as a $$byproduct.

Question 8

Which metabolic pathway is the most energy-efficient for CO$$_2$$ fixation, requiring only 1 ATP per 3 CO$$_2$$ fixed?

Accepted Answer

Reductive acetyl-CoA pathway

Question 9

A wastewater treatment plant is experiencing high levels of fixed nitrogen in its effluent. Which microbial process would be most beneficial to reduce this nitrogen load?

Accepted Answer

Anammox (anaerobic ammonia oxidation)

Question 10

Which of the following best explains why syntrophy is essential in anoxic environments for the degradation of fatty acids?

Accepted Answer

Syntrophy allows one microbe to oxidize fatty acids while another consumes H$$_2$$, making the overall reaction exergonic.

Question 11

Which pigment is primarily responsible for the absorption of light in oxygenic photosynthesis?

Accepted Answer

Chlorophyll a

Question 12

What is the main ecological consequence of denitrification in agricultural soils?

Accepted Answer

Loss of fixed nitrogen as N$$_2$$ gas, reducing soil fertility.

Question 13

Which of the following is a unique feature of the chlorosome found in green sulfur bacteria?

Accepted Answer

It allows growth at extremely low light intensities by functioning as a giant antenna system.

Question 14

Which process is responsible for the biological production of methane in freshwater sediments?

Accepted Answer

Methanogenesis

Question 15

During fermentation, how is ATP primarily generated?

Accepted Answer

By substrate-level phosphorylation

Question 16

Which of the following is a major function of carotenoids in photosynthetic microorganisms?

Accepted Answer

They act as photoprotective agents, quenching toxic oxygen species.

Question 17

A bacterium is isolated from an acidic, iron-rich environment and is found to oxidize Fe$$^{2+} to Fe$^{3+}. $$Which of the following is true about its metabolism?

Accepted Answer

It must oxidize large amounts of Fe$$^{2+} to $$generate enough energy for growth due to the poor energetic yield of iron oxidation.

Question 18

Which of the following best describes the role of reverse electron transport in chemolithotrophic bacteria?

Accepted Answer

It enables the reduction of NAD(P)$$^+ to $$NAD(P)H using energy from the proton motive force.

Question 19

Which of the following is a key ecological role of nitrifying bacteria in the nitrogen cycle?

Accepted Answer

They oxidize ammonia to nitrite and nitrate, making nitrogen available for plant uptake.

Metabolic Diversity of Microorganisms: Energy, Redox, and Major Pathways

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