AQA A2 BIOLOGY UNIT 4: Nutrient Cycles

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  • Created on: 18-04-14 14:16
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The greenhouse effect is a natural process that occurs all the time and keeps average global
temperatures at around 17 degrees.
The most important greenhouse gas is carbon dioxide.
It is highly abundant and it remains in the atmosphere for much longer than other greenhouse gases.
50-70% of global warming is due to carbon dioxide in the atmosphere.
It is mainly a result of human activities that the concentration of carbon dioxide is increasing,
enhancing greenhouse effects and causing environmental concerns.
Another greenhouse gas is methane.
Methane is produced wen organisms break down the organic molecules of which organisms are made.
This occurs mostly in two situations:
· When decomposers break down the dead remains of organisms
· When microorganisms in the intestines of primary consumers such as cattle digest the food that has
been eaten

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The concentrations of the greenhouse gases may be very small, but they are increasing.
The result of these increases is the enhanced greenhouse effect, which is causing more heat to be
trapped on Earth, leading to an increase in mean global temperature called global warming.
Effects of Global Warming
Global warming is expected to bring about changes in temperature and precipitation, the timing of the
seasons and the frequency of extreme events such as storms, floods and drought.…read more

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Energy enters an ecosystem as sunlight and is lost as heat.
This heat cannot be recycled.
The flow of energy through an ecosystem is therefore in one direction, that is, it is linear.
The flow of nutrients within an ecosystem is not linear, but cyclic.…read more

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Carbon, in the form of CO2 from air and water, is absorbed by plants when they carry out
It becomes carbon compounds in plant tissues.
Carbon is passed on to primary consumers when they eat the plants.
It's passed on to secondary and tertiary consumers when they eat other consumers .
On their death, both plants and animals are usually broken down by saprobiotic microorganisms known
collectively as decomposers.
Saprobiotic microorganisms secrete enzymes on to the dead organisms.…read more

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Plants take up most of the nitrogen
they need in the form of nitrate ions
which are absorbed using active
transport by the root hairs.
Nitrate ions are very soluble and
leach through the soil.
In natural ecosystems, the nitrate
levels are restored through recycling
of nitrogen-containing compounds.
In agricultural ecosystems, the level
of nitrate can be further increased by
the use of fertilisers.…read more

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All plants need mineral ions, especially nitrogen.
Intensive food production makes large demands on the soil because mineral ions are continually taken
up by the crops being grown on it.
Mineral ions crops have absorbed are being removed.
In natural ecosystems the minerals that have been removed from the soil by plants are removed when
the plant dies and is broken down by microorganisms.
In agricultural systems the crop is harvested and then transported from its point of origin.…read more

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Effect Impact
Reduced species Because nitrogen-rich soils favour the growth of grasses ,
diversity nettles and other rapidly growing species.
These outcompete many other species, which die as a result
Leaching Which may lead to pollution of watercourses
Eutrophication Caused by leaching of fertiliser into watercourses
Leaching is the process by which nutrients are removed from the soil.
Rain water will dissolve any soluble nutrients, such as nitrates, and carry them deep into the soil and
eventually beyond the reach of plant roots.…read more


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