AQA A2 Unit 4 Nutrient Cycles

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The Carbon Cycle

-Carbon is removed from the atmosphere by photosynthesis and returned by respiration.

-Incomplete decomposition can result in the formation of fossil fuels, which have locked up large amounts of carbon for millions of years. The combustion of these fossil fuels returns carbon dioxide to the air.

-Carbon dioxide is a greenhouse gas, helping to prevent long-wave radiation from leaving the earth. This is essential, as without it the earth the earth would be too cold to sustain life.

-The concentration of carbon dioxide, and also of other greenhouse gases such as methane, has been increasing. This has led to an enhanced greenhouse effect, which is casuing climate change, including global warming. Human activities such as the burning of fossil suels and deforestation are conributing to these changes.

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Carbon Cycle Continued...

-Increased carbon dioxide concentrations may result in increased rates of photosynthesis, and therefore increased productivity and yield of crop plants. However, in some parts of the world, increased temperatures may reduce yields, or even means that some types of crop plants can no longer be grown there.

-Warmer winters and longer smmers are likely to affect the life cycles of insects and increase thier populations. This could mean that insect pests may become a greater threat to health of humans and other animals, and may also reduce crop yeilds.

-Animals and plants adapted to living in our current climate may not be abke to survive in the same areas in the future. For some, this may mean extinction if they cannot move to cooler habitats.

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Nitrogen Cycle

-Nitrogen gas is too unreactive to be used by plants, and must be converted into a comound such as nitrate or ammonia in order to become available to them. This is called nitrogen fixation. some bacteria are important nitrogen fixers.

-Animals obtain thier nitrogen by feeding on plants.

-Remains of dead plants and animals, and thier waste products, contain protiens and other nitrogenous substances. These are broken down by saprobiotic decomposers to form ammonia.

-Nitrifying bacteria oxidise ammonia to nitrite and nitrate ions.

-Denitrifing bacteria reduce nitrate ions to nitrogen.

-Pollution of waterways by nitrogen-containing fertilisers leads to eutrophication, in which excessive growth of the population of oxygen-requiring bacteria depletes the water of disolved oxygen.

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