Cycles Within Ecosystems Flashcards
The carbon cycle
Carbon is cycled through the living and non-living parts of ecosystems, in different forms at different stages of the carbon cycle. Carbon dioxide from the atmosphere is converted to complex carbon compounds in plants during photosynthesise. This is often called the ‘fixing’ of carbon by plants. Respiration in plants returns some of this fixed carbon back to the atmosphere as carbon dioxide. Carbon in the form of complex carbon compounds passes along the food chain.
At each stage, some of this carbon is released as carbon dioxide to the atmosphere as the result of respiration.
When organisms die, their bodies decay as they are digested by decomposers (bacteria and fungi). This is also known as decomposition. Carbon dioxide is released when the decomposers respire using the carbon compounds from the dead organisms.
If dead organic material is buried too quickly by sediment of water for decomposers to cause decay and remains buried, then it may be converted to other complex carbon compounds. Peat is formed when mosses and other plants are buried in swampy grounds for hundred of years. Over many millions of years, where there were once huge forests growing in swampy regions, heat and pressure over many millions of years also produce oil and natural gas from the decaying bodies of tiny marine organisms that were buried in sediment at the bottom of oceans. Peat, coal and oil are fossil fuels. We can release the carbon from the complex carbon compounds in fossil fuels, as well as from other sources such as wood, into the air as carbon dioxide during combustion when we burn them.
Summary of cycle in a picture on pg284
The nitrogen cycle
Living things need nitrogen to make proteins, which are used, for example, to make new cells during growth. Air is 79% nitrogen gas, but nitrogen gas is very unreactive and cannot be used by plants or animals.
The nitrogen cycle describes the way in which nitrogen passes between the living and non-living parts of an ecosystem. Animals take in nitrogen in the form of proteins when they eat plant tissue or animal tissue.
