AP Environmental Science : Nitrogen Cycle
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Example Question #2 : Biochemical Cycles
Which of the following is the major reservoir of nitrogen in the nitrogen cycle?
Soil
Bacteria
Atmoshpere
Plants
Animals
Atmoshpere
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 #1 : Nitrogen Cycle
With reference to the biogeochemical cycles, how do elements and matter flow in the environment?
From a sink to a source
From a source to a source
From a sink to a sink
From a source to a sink
From a source to a sink
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 : Biochemical Cycles
Why can't plants utilize atmospheric nitrogen for their metabolic processes?
Atmospheric nitrogen is poisonous to plants
It must first be fixed by cyanobacteria into ammonia
Plants cannot absorb nitrogen unless it is in the form of nitrates
Plants do not need nitrogen for their metabolic processes
It must first be fixed by cyanobacteria into ammonia
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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