Question 1

Which of the following best describes the role of methanogens in the carbon cycle?

Accepted Answer

They reduce carbon dioxide to methane under anaerobic conditions.

Question 2

In marine environments, what is the primary fate of fixed carbon produced by phytoplankton?

Accepted Answer

It is transferred to higher trophic levels and eventually sinks as particulate organic carbon.

Question 3

Which equation correctly represents the process of acetogenesis?

Accepted Answer

$2CO_2 + 4H_2 \rightarrow CH_3COOH + 2H_2O$

Question 4

Which microbial process is most stimulated by the addition of inorganic fertilizers to soil?

Accepted Answer

Nitrification

Question 5

What is the main ecological significance of syntrophy in anaerobic environments?

Accepted Answer

It enables the cooperative degradation of substrates that cannot be metabolized by one organism alone.

Question 6

Which of the following is a correct description of the redox cycle for carbon in prokaryotes?

Accepted Answer

CO$_2$ is fixed by oxygenic photosynthesis and released by aerobic respiration.

Question 7

Cellulases are enzymes that primarily catalyze which reaction?

Accepted Answer

Hydrolysis of cellulose into glucose

Question 8

Why is proximity important for syntrophic microbial interactions, especially in hydrogen processing?

Accepted Answer

It allows efficient transfer of hydrogen between partners, minimizing energy loss.

Question 9

Which process is responsible for the aerobic oxidation of methane in the environment?

Accepted Answer

Methanotrophy

Question 10

In terrestrial environments, what is the primary role of lignocellulose-degrading microbes?

Accepted Answer

They break down complex plant polymers into simpler compounds for further microbial processing.

Question 11

Which of the following best explains why oxygen availability affects the fate of fixed carbon in soils?

Accepted Answer

Oxygen allows for aerobic respiration, leading to complete mineralization of organic carbon to CO$_2$.

Question 12

Which equation represents the process of methanogenesis from CO$_2$ and H$_2$?

Accepted Answer

$CO_2 + 4H_2 \rightarrow CH_4 + 2H_2O$

Question 13

Which of the following is a primary fermentation product in anaerobic microbial metabolism?

Accepted Answer

Lactic acid

Question 14

What is the main difference between primary and secondary fermentation in microbial communities?

Accepted Answer

Secondary fermentation involves the further breakdown of primary fermentation products by other microbes.

Question 15

Which process is most likely to occur in anoxic sediments of a freshwater lake?

Accepted Answer

Methanogenesis

Question 16

Which of the following statements about the processing of fixed carbon in marine environments is correct?

Accepted Answer

A significant portion of fixed carbon is exported to the deep ocean as particulate organic carbon.

Question 17

What is the role of hydrogenotrophic methanogens in the carbon cycle?

Accepted Answer

They reduce carbon dioxide to methane using hydrogen as an electron donor.

Question 18

Which of the following best describes the process of syntrophy in secondary fermentation?

Accepted Answer

Two organisms cooperate to degrade a substrate that neither can degrade alone.

Question 19

Which of the following is a key factor that determines the efficiency of hydrogen transfer in syntrophic microbial communities?

Accepted Answer

Physical proximity of hydrogen-producing and hydrogen-consuming microbes

Question 20

Which of the following is NOT a product of fermentation in anaerobic microbial metabolism?

Accepted Answer

Methane

Microbial Roles in the Carbon Cycle: Processes, Pathways, and Ecological Importance

Study Guide - Practice Questions