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  • Recycling.
    • Carbon cycle
      • The element of carbon is present in all living organisms.It is recycled through various processes described in the carbon cycle.
        • 1. Carbon enters the atmosphere as carbon dioxide from respiration and combustion.
        • 2. Carbon dioxide is absorbed by produces  to make carbohydrates in photosynthesis.
        • 3. Animals feed on the plants causing the carbon compounds to enter the food chain. Most of the carbon they consume is exhaled as carbon dioxide during respiration. The animals and plants eventually die.
        • The dead organisms are eaten by decomposers, and the carbon in their bodies is returned to the atmosphere as carbon dioxide. In some conditions decomposition is blocked. The plant and animal materiel may then be used as fossil fuel for combustion in the future.
      • Nitrogen is essential for making amino acids to make proteins. The nitrogen cycle describes the ways in which nitrogen is recycled.
      • Most of the chemicals that make up living tissue contain carbon. When organisms die the carbon is recycled so that it can be used by future generations.
    • Nitrogen cycle
      • Nitrogen is essential for the formation of amino acids in proteins. The nitrogen model is a model that explains how nitrogen is recycled.
        • Once in plants nitrates are used to make proteins. When animals feed on the plant nitrogen compounds such as protein enter into the food chain.
        • When animals and plants die, the nitrogen compounds are broken down by soil bacteria, fungi and other decomposers. In this way nitrogen compounds return to the soil where they may be absorbed by plants again.
      • About 78% of the air is nitrogen. Because nitrogen is so unreactive it cannot be used by plants to make protein.
      • Nitrates contain nitrogen. Nitrates are soluble in water, so plants are able to absorb them through their roots through the soil.


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