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Recycling – Revision Pack (B2) The Carbon Cycle: Carbon is one of many elements which are found in living organisms. Carbon needs to be recycled so that it can become available to other living organisms. In photosynthesis carbon dioxide is removed from the air. Feeding passes carbon compounds along a food chain or web. Carbon dioxide can be released into the air by: - Plants and animals respiring Soil bacteria and fungi acting as decomposers The burning of fossil fuels Carbon dioxide is absorbed from the air by oceans. Marine organisms make shells made out of carbonates, which become limestone rocks. The carbon in the limestone can return to the air as carbon dioxide during volcanic eruptions or weathering. The Nitrogen Cycle: Eaten Proteins in plants Plants take in nitrogen as nitrates from the soil to make protein for growth. Feeding passes nitrogen compounds along a food chain or web. Plants and animals die and decay Proteins in Animals The nitrogen compounds in dead plants and animals are broken down by decomposers and return to the soil. A number of microorganisms are responsible for the recycling of nitrogen. Decomposers Nitrates in the soil For example, decomposers are soil bacteria and fungi and convert proteins and urea into ammonia. Recycling – Revision Pack (B2) Bacteria Nitrifying bacteria Job in recycling nitrogen Converts ammonia into nitrates Denitrifying bacteria Converts nitrates into nitrogen gas Nitrogen-Fixing bacteria Live in the root nodules or soil, and fix nitrogen gas in the air into nitrates in the soil – also occurs by the action of lightning Keeping Decomposers Working: For decomposers to be able to break down dead material in soil, they need oxygen and a suitable pH. Decay will therefore be slower in waterlogged soils because there is less oxygen. Decay will also be slower in more acidic conditions. Recycling – Revision Pack (B2) Past Papers: PPQ(1): PPQ(2): Recycling – Revision Pack (B2) PPQ(3): PPQ(4): Recycling – Revision Pack (B2) Mark Schemes: PPQ(1): PPQ(2): PPQ(3): PPQ(4):