Question 1

Which process in the nitrogen cycle converts atmospheric nitrogen ($$N_2) $$into a form usable by plants?

Accepted Answer

Nitrogen fixation

Question 2

A farmer notices that his crops are not growing well despite adequate water and sunlight. Soil tests reveal low levels of ammonium ($$NH_4$$^+$$) and nitrate (NO_3$^-). $$Which group of organisms is most likely deficient in his soil?

Accepted Answer

Nitrogen-fixing bacteria

Question 3

Which of the following best describes the role of decomposers in the nitrogen cycle?

Accepted Answer

They break down organic matter, releasing ammonium ($$NH_4$$^+$$).

Question 4

What is the correct sequence of processes that occur when a plant dies and its nitrogen is returned to the atmosphere?

Accepted Answer

Decomposition → Ammonification → Nitrification → Denitrification

Question 5

Which chemical equation represents the process of nitrification in the nitrogen cycle?

Accepted Answer

$$NH_4$$^+ \rightarrow $$NO_2$$^- \rightarrow $$NO_3$$^-$$

Question 6

Denitrifying bacteria play a crucial role in the nitrogen cycle by:

Accepted Answer

Converting $$NO_3$$^-$$ to N_2$ gas

Question 7

Which reservoir contains the largest amount of nitrogen on Earth?

Accepted Answer

Atmosphere ($$N_2$$ gas)

Question 8

A scientist adds $$^{15}N-$$labeled ammonium to a soil sample. After several days, she detects $$^{15}N in $$nitrate ($$NO_3$$^-$$). Which process is responsible for this transformation?

Accepted Answer

Nitrification

Question 9

Which process allows plants to incorporate nitrogen from the soil into amino acids and proteins?

Accepted Answer

Assimilation

Question 10

If a wetland ecosystem is drained and exposed to air, which nitrogen cycle process is most likely to increase, potentially releasing more $$N_2$$ gas?

Accepted Answer

Denitrification

Question 11

Which of the following is a direct consequence of excessive use of fossil fuels on the nitrogen cycle?

Accepted Answer

Release of nitrogen oxides ($$NO_x) $$into the atmosphere

Question 12

A plant absorbs $$NO_3$$^-$$ from the soil. Which process must occur next for the nitrogen to become part of the plant's proteins?

Accepted Answer

Assimilation

Question 13

Which of the following scenarios best illustrates the process of nitrogen fixation?

Accepted Answer

Bacteria in root nodules convert $$N_2$$ gas into $$NH_3$$

Question 14

Which process is responsible for converting organic nitrogen in dead organisms into ammonium ($$NH_4$$^+$$)?

Accepted Answer

Decomposition (ammonification)

Question 15

A water sample from a pond contains high levels of $$NO_3$$^-$$. Which process could reduce these levels and return nitrogen to the atmosphere?

Accepted Answer

Denitrification

Question 16

Which of the following is NOT a reservoir of nitrogen in the nitrogen cycle?

Accepted Answer

Glucose in plants

Question 17

Which process is most directly responsible for the conversion of $$NH_4$$^+$$ to NO_2$^-$$ and then to $$NO_3$$^-$$?

Accepted Answer

Nitrification

Question 18

A scientist observes that after adding a certain bacteria to soil, the concentration of $$N_2$$ gas in the atmosphere above the soil increases. Which process is most likely being carried out by these bacteria?

Accepted Answer

Denitrification

Question 19

Which process in the nitrogen cycle is most affected by the presence of legumes in an ecosystem?

Accepted Answer

Nitrogen fixation

Question 20

Which of the following best explains why nitrogen is often a limiting nutrient in ecosystems, despite its abundance in the atmosphere?

Accepted Answer

Atmospheric $$N_2 is $$inert and cannot be directly used by most organisms.

The Nitrogen Cycle: Processes and Reservoirs

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