19.2 Nutrient Cycles (Cambridge (CIE) O Level Biology): Flashcards
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- FrontThe Carbon Cycle
How is carbon removed from the atmosphere?
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Cards in this collection (24)
How is carbon removed from the atmosphere?
By photosynthesis in plants, which take in carbon dioxide.
Why do living organisms need nitrogen?
To make proteins.
How is carbon passed from plants to animals?
By feeding (eating).
Why can plants and animals not absorb nitrogen gas directly from the air?
Nitrogen gas is very stable (its atoms are held by a strong triple bond), so it cannot be absorbed.
Which process returns carbon dioxide to the atmosphere from living organisms?
Respiration, carried out by plants, animals and microorganisms.
Define nitrogen-fixing bacteria.
Bacteria that convert nitrogen gas from the air into nitrates in the soil.
Define combustion.
The burning of fuels, which releases carbon dioxide into the atmosphere.
Where are nitrogen-fixing bacteria found?
In two places:
free-living in the soil
in the root nodules of leguminous plants (peas, beans, clover)
When fossil fuels are burned, carbon combines with oxygen and is released into the atmosphere.
When fossil fuels are burned, carbon combines with oxygen and carbon dioxide is released into the atmosphere.
Besides bacteria, what natural event can fix nitrogen gas from the air?
Lightning, which splits nitrogen molecules to form nitrous oxides that dissolve in rain.
True or False?
Fossil fuels form from dead organisms over millions of years under great pressure.
True.
They form when organisms die where decomposing microorganisms are absent, over millions of years.
Plants absorb from the soil and use the nitrogen in them to make proteins.
Plants absorb nitrates from the soil and use the nitrogen in them to make proteins.
Why does deforestation increase the carbon dioxide content of the atmosphere?
Fewer producers remain to remove carbon dioxide by photosynthesis, and burning the trees releases more.
How does nitrogen from animal waste and dead organisms return to the soil?
As ammonium compounds, released when decomposers break down proteins and urea.
Carbon dioxide is taken out of the atmosphere by plants for the process of .
Carbon dioxide is taken out of the atmosphere by plants for the process of photosynthesis.
Define nitrifying bacteria.
Bacteria that convert ammonium compounds into nitrites and then nitrates.
True or False?
Carbon is an endless resource that never needs to be recycled.
False.
There is only a finite amount of carbon, so it must be recycled to make new organisms.
True or False?
Denitrifying bacteria convert nitrates in the soil back into nitrogen gas.
True.
They are found in poorly aerated soil and reduce its fertility.
Under what conditions do dead organisms form fossil fuels?
When they die where decomposing microorganisms are absent, over millions of years under pressure.
bacteria in poorly aerated soil convert nitrates back into nitrogen gas.
Denitrifying bacteria in poorly aerated soil convert nitrates back into nitrogen gas.
What name is given to the burning of trees that releases carbon dioxide during deforestation?
Combustion
How can farmers reduce the activity of denitrifying bacteria?
By ploughing and turning over the soil to let in more air (oxygen).
Give one human activity that is increasing atmospheric carbon dioxide.
Burning fossil fuels (deforestation also contributes).
True or False?
Nitrifying bacteria remove nitrates from the soil and release nitrogen gas.
False.
That is done by denitrifying bacteria; nitrifying bacteria produce nitrates from ammonium compounds.
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