Question 1

Which of the following best describes the process of biological nitrogen fixation?

Accepted Answer

Reduction of $N_2$ gas to $NH_3$ by specialized prokaryotes using the enzyme nitrogenase

Question 2

Which equation correctly represents the overall reaction for nitrogen fixation?

Accepted Answer

$N_2 + 8H^+ + 8e^- \rightarrow 2NH_3 + H_2$

Question 3

Which group of microorganisms is primarily responsible for symbiotic nitrogen fixation in legumes?

Accepted Answer

Rhizobium

Question 4

In the nitrogen cycle, which process is carried out by ammonia-oxidizing bacteria (AOB)?

Accepted Answer

Oxidation of $NH_3$ to $NO_2^-$

Question 5

Which of the following is a biomarker for ammonia-oxidizing archaea (AOA)?

Accepted Answer

Special lipid called crenarchaeol

Question 6

What is the main ecological significance of nitrate reduction in aquatic environments?

Accepted Answer

It removes bioavailable nitrogen by converting $NO_3^-$ to $N_2$, reducing eutrophication

Question 7

Which of the following reactions represents the first step of nitrification?

Accepted Answer

$NH_3 + O_2 \rightarrow NO_2^- + H_2O$

Question 8

Which of the following is NOT a characteristic of free-living diazotrophs?

Accepted Answer

They require symbiotic relationships with plants to fix nitrogen

Question 9

Anabaena is able to fix nitrogen in aerobic environments due to which adaptation?

Accepted Answer

Formation of heterocysts that provide an anaerobic environment for nitrogenase

Question 10

Which process is responsible for the conversion of $NO_2^-$ to $NO_3^-$ in the nitrogen cycle?

Accepted Answer

Nitrite oxidation by nitrite-oxidizing bacteria (NOB)

Question 11

A farmer wants to increase nitrogen availability in soil for crops. Which microbial process should be promoted?

Accepted Answer

Nitrogen fixation by symbiotic diazotrophs

Question 12

Which of the following is a waste process in the nitrogen cycle?

Accepted Answer

Ammonification

Question 13

Which of the following is true about the enzyme nitrogenase?

Accepted Answer

It is highly sensitive to oxygen and requires protection in aerobic environments

Question 14

Which of the following is a correct multi-step pathway for the conversion of ammonia to nitrate in the environment?

Accepted Answer

$NH_3 \xrightarrow{AOB} NO_2^- \xrightarrow{NOB} NO_3^-$

Question 15

Which of the following is a major difference between assimilatory and dissimilatory nitrate reduction?

Accepted Answer

Assimilatory reduction incorporates $NO_3^-$ into biomass, while dissimilatory reduction uses $NO_3^-$ as a terminal electron acceptor

Question 16

Which of the following is a correct equation for nitrate reduction to nitrogen gas?

Accepted Answer

$C_6H_{12}O_6 + 4NO_3^- \rightarrow 2N_2 + 6CO_2 + 6H_2O$

Question 17

Which of the following organisms is most likely to be found in oxygen minimum zones performing anaerobic nitrate reduction?

Accepted Answer

Denitrifying bacteria

Question 18

Which of the following is a key feature of symbiotic diazotrophs in root nodules?

Accepted Answer

They form specialized structures to protect nitrogenase from oxygen

Question 19

Which process in the nitrogen cycle is most directly responsible for the loss of nitrogen from agricultural soils to the atmosphere?

Accepted Answer

Denitrification

Nitrogen Biogeochemical Cycle II: Microbial Processes and Ecological Roles

Study Guide - Practice Questions