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Nitrogen Cycle • • • • • Nitrogen is essential to life – it is a component of protein used for growth and repair) Nitrogen composes 80% of the atmosphere but it is not directly available in this form. Plants get protein from the soil as nitrates Animals get protein from plants / animals / bacteria We depend on methods of replenishing the nitrates in the soil. 1. Decomposition dead organic matter is broken down by saprophytes (i.e. bacteria / fungi) into ammonia or ammonia compounds 2. Nitrification Ammonia compounds are oxidised by nitrifying bacteria into nitrites and then into nitrates. 3. Nitrates The active uptake of nitrates requires energy. The nitrates are taken up by the root hair cell and are combined with carbohydrates from photosynthesis into proteins 4. Lightning the high temperature of the flashes combine the oxygen and nitrogen to form nitric or nitrous oxide gases. The gasses dissolve in the moisture to form acid. These acids (nitric acids) are washed into the soil with rain. They combine with other chemicals in the soil forming ammonium compounds. 5. Nitrates The active uptake of nitrates requires energy. The nitrates are taken up by the root hair cell and are combined with carbohydrates from photosynthesis into proteins 6. Symbiotic bacteria Symbiosis is the living together of two different species for their mutual benefits. 7. Leguminous plants These contain symbiotic bacteria on the end of their roots. These bacteria trap the atmospheric nitrogen and convert it into ammonium compounds in the soil. The plant gains nitrates (and CO2) and the bacteria gains carbohydrates – mutual benefit! 8. Addition of manure / compost Increases nitrates in the soil. This is done by the cycle of decomposition 9. Factory made fertiliser This is readily soluble and so mineral ions are readily available to the plant. Overuse destroys crumb structure of the soil. It also increases the acidity and pollution. 10. Denitrification In water logged soil, there is no oxygen present. This means that the roots cannot respire. The anaerobic bacteria flourish and use the nitrates as a source of energy – releasing nitrogen gas into the atmosphere – results in poor plant growth. Nitrogen gas (N2) in the atmosphere food for animals death death Nitrogen fixation: Can occur with energy from lightning or can be carried out by nitrogen fixing bacteria (may live in plant roots) decomposers – saprophytes (i.e. bacteria / fungi) convert the dead organic matter to ammonium compounds Nitrate ions absorbed by plants by diffusion and active transport Ammonium compounds / ammonia Denitrification – removes the nitrates in the soil. Carried out by denitrifying bacteria – only occurs in waterlogged conditions. Nitrifying bacteria Nitrate ions (NO3 ) in soil solution (aerobic conditions) Nitrification