The Nitrogen Cycle (College Board AP® Environmental Science): Flashcards
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- FrontThe Nitrogen Cycle
Define nitrogen cycle.
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Define nitrogen cycle.
The nitrogen cycle is the set of processes by which nitrogen atoms and nitrogen-containing molecules move through the atmosphere, soil, water and living organisms.
Why is nitrogen essential for life?
Nitrogen is essential for life because it is a key component of proteins and nucleic acids (DNA and RNA).
The decomposition of dead plants and animals releases nitrogen as (NH₄⁺).
The decomposition of dead plants and animals releases nitrogen as ammonium (NH₄⁺).
Besides lightning and decomposition, what are two sources of nitrogen compounds?
Two other sources of nitrogen compounds are fertilizer application and animal waste.
What are examples of nitrogen sinks?
Nitrogen sinks include the atmosphere, soil, plants and animals and oceans.
Define nitrogen reservoir.
A nitrogen reservoir is a place where nitrogen compounds are stored within the nitrogen cycle.
True or False?
Soil and living organisms are long-term nitrogen reservoirs.
False.
Soil and living organisms are short-term reservoirs (days to decades); ocean sediments and sedimentary rocks are long-term reservoirs (thousands to millions of years).
Nitrogen gas (N₂) makes up about % of Earth's atmosphere.
Nitrogen gas (N₂) makes up about 78% of Earth's atmosphere.
True or False?
Soil is the largest nitrogen reservoir.
False.
The atmosphere is the largest nitrogen reservoir, holding nitrogen gas in its inert form (N₂).
Define nitrogen fixation.
Nitrogen fixation is the process that converts nitrogen gas (N₂) from the atmosphere into forms that plants can use, such as ammonia (NH₃).
Which bacteria carry out biotic nitrogen fixation in legume root nodules?
Nitrogen-fixing bacteria such as Rhizobium use enzymes to convert nitrogen gas into ammonia.
How does lightning fix nitrogen?
The high energy from lightning breaks nitrogen molecules, allowing the nitrogen to react with oxygen to form nitrates.
After a thunderstorm, how do nitrates reach the soil?
After a thunderstorm, nitrates are deposited into the soil by rain, enriching it for plant growth.
Define assimilation.
Assimilation is the uptake of ammonium (NH₄⁺) and nitrates (NO₃⁻) by plant roots.
True or False?
Plants use assimilated nitrogen to make chlorophyll.
True.
Assimilated nitrogen is synthesized into plant tissue, including chlorophyll for photosynthesis.
How do animals obtain nitrogen?
Animals obtain nitrogen by eating plants, or by eating other animals that have eaten plants.
Which process returns nitrogen to the atmosphere as a gas?
Denitrification returns nitrogen to the atmosphere as a gas, completing the cycle.
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