AP Environmental Science : Nitrogen Cycle

Study concepts, example questions & explanations for AP Environmental Science

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Example Questions

Example Question #1 : Nitrogen Cycle

Which of the following is the major reservoir of nitrogen in the nitrogen cycle?

Possible Answers:

Bacteria

Plants

Atmoshpere

Animals

Soil

Correct answer:

Atmoshpere

Explanation:

Although all of the above are part of the nitrogen cycle, the major reservoir for nitrogen is the atmosphere. The atmosphere contains nitrogen gas which cannot be extracted by plants or animals from the atmosphere. From its reservoir in the atmosphere, nitrogen gas is combined with oxygen to  form nitrate and carried to Earth dissolved in rain. Nitrogen-fixing bacteria produce ammonia. This is absorbed by plants and other producers and incorporated into biological molecules that are passed through the trophic levels. Nitrate and ammonia are released by excretion or by decomposer bacteria. Other bacteria convert these molecules back to atmoshperic nitrogen, completing the cycle.

Example Question #2 : Nitrogen Cycle

With reference to the biogeochemical cycles, how do elements and matter flow in the environment? 

Possible Answers:

From a source to a sink

From a sink to a source

From a sink to a sink

From a source to a source

Correct answer:

From a source to a sink

Explanation:

A source is an organism or physical body that releases a certain compound or element. Through energy dynamics or physical manipulations of the environment, it reaches the sink. The sink is the receiver of the element and can act as another source for a different organisms or physical body. This is how matter travels in the environment, from pairs of source to sink dynamics. 

Example Question #3 : Nitrogen Cycle

Why can't plants utilize atmospheric nitrogen for their metabolic processes? 

Possible Answers:

Atmospheric nitrogen is poisonous to plants 

It must first be fixed by cyanobacteria into ammonia 

Plants do not need nitrogen for their metabolic processes

Plants cannot absorb nitrogen unless it is in the form of nitrates

Correct answer:

It must first be fixed by cyanobacteria into ammonia 

Explanation:

According to the principles of the Nitrogen cycle, plants can only absorb nitrogen in the form of ammonia. This is achieved by nitrogen-fixing bacteria that convert atmospheric nitrogen into a form usable by plants. Plants excrete nitrogen in the form of waste as nitrates which are absorbed by animals. 

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