Question 1

Which of the following best describes a biogeochemical cycle?

Accepted Answer

The flow of any element in a cyclic manner through biological, geological, and chemical forms.

Question 2

In the nitrogen cycle, which chemical form of nitrogen is most abundant in the atmosphere?

Accepted Answer

Dinitrogen gas ($N_2$)

Question 3

Which process in the nitrogen cycle converts atmospheric $N_2$ into ammonia ($NH_3$) usable by living organisms?

Accepted Answer

Nitrogen fixation

Question 4

What is the correct sequence of oxidation states for nitrogen in the following compounds: $NH_4^+$, $NO_2^-$, $NO_3^-$, $N_2$?

Accepted Answer

$NH_4^+$: -3, $NO_2^-$: +3, $NO_3^-$: +5, $N_2$: 0

Question 5

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

Accepted Answer

Denitrification ($NO_3^- \rightarrow N_2$)

Question 6

A farmer applies excess fertilizer to a field, resulting in runoff into a nearby pond. Which process is most likely to occur, leading to eutrophication?

Accepted Answer

Rapid assimilation of $NO_3^-$ by aquatic plants and algae

Question 7

Which microbial process is responsible for converting $NH_4^+$ to $NO_2^-$ and then $NO_3^-$ in soils?

Accepted Answer

Nitrification

Question 8

Why is $N_2$ the dominant form of nitrogen in the atmosphere?

Accepted Answer

It is inert due to the triple bond between nitrogen atoms, making it stable.

Question 9

Which of the following human activities has most significantly altered the global nitrogen cycle?

Accepted Answer

Increased use of synthetic fertilizers in agriculture

Question 10

A wastewater treatment plant uses microbial processes to remove nitrogen from effluent. Which process is most important for converting $NO_3^-$ to $N_2$ gas?

Accepted Answer

Denitrification

Question 11

Which of the following is NOT a physical or chemical form of nitrogen found in the environment?

Accepted Answer

Methane ($CH_4$)

Question 12

During the process of ammonification, which transformation occurs?

Accepted Answer

Conversion of organic nitrogen to $NH_4^+$

Question 13

Which of the following best explains why eutrophication can lead to fish kills in aquatic ecosystems?

Accepted Answer

Algal blooms consume oxygen during decomposition, leading to hypoxia.

Question 14

Which process in the nitrogen cycle is primarily carried out by anaerobic bacteria?

Accepted Answer

Denitrification

Question 15

A soil sample is found to have high concentrations of $NO_3^-$. Which process is most likely to be occurring at a high rate?

Accepted Answer

Nitrification

Question 16

Which of the following equations correctly represents the process of denitrification?

Accepted Answer

$NO_3^- \rightarrow NO_2^- \rightarrow NO \rightarrow N_2O \rightarrow N_2$

Question 17

Which of the following is a consequence of increased nitrogen input from human activities?

Accepted Answer

Increased greenhouse gas emissions such as $N_2O$

Question 18

Which of the following statements about chemolithotrophic oxidation in the nitrogen cycle is correct?

Accepted Answer

It is the process by which $NH_4^+$ is oxidized to $NO_2^-$ and then $NO_3^-$.

Question 19

Which of the following is an assimilatory process in the nitrogen cycle?

Accepted Answer

Incorporation of $NO_3^-$ into organic molecules by plants

Question 20

A lake receives runoff rich in $NH_4^+$ and $NO_3^-$. Which sequence of microbial processes is most likely to occur, leading to nitrogen loss from the system?

Accepted Answer

Nitrification followed by denitrification

Nitrogen Biogeochemical Cycle I: Microbial Roles and Environmental Impact

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