Decay is an essential life process, which helps to digest food and recycle materials. Bacteria and fungi are the main groups of decomposer. They release enzymes to break down compounds, so that they can absorb the nutrients. We can preserve our food, for example by freezing or canning, to remove the conditions needed for decay to happen.
Microorganisms are important for decay
Decay is what happens when dead animals and plants break down. The key factors involved in decay are:
- Amount of oxygen
- Amount of water
- The presence of microorganisms
Microorganisms are important in decay. For example, they are used to break down human waste (sewage) and plant waste (compost). Decay recycles important nutrients for plant growth.
The main groups of decomposer organisms are bacteria and fungi. Bacteria are single-celled microscopicmicroscopic: Extremely small; something which can only be seen through a microscope organisms. Fungi are often larger organisms that include moulds and mushrooms. They both cause decay by releasing enzymes [enzyme: A protein which speeds up chemical reactions. ] onto the dead animal or plant. These break down complex compounds into simple soluble ones that can be absorbed by decomposers. Organisms that feed on dead material in this way are called saprophytes.
Decomposers such as bacteria and fungi cause decay at a microscopic level. Other larger organisms, called detritivoresdetritivore: An organism that feeds on dead organisms and waste eg earthworm., help speed up decay by feeding on detritusdetritus: Particulate matter formed by the decay or disintegration of an organic substance.. This is dead and decaying material. They break it down into smaller pieces, so increasing the surface area for the bacteria and fungi. Detritivores include:
- Earthworms that help break down dead leaves
- Maggots that feed on animal tissue
- Woodlice that break down wood
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The carbon cycle
The amount of carbon dioxide in the atmosphere is controlled by the carbon cycle.
Processes that remove carbon dioxide from the air:
- photosynthesis [photosynthesis: The chemical change that occurs in the leaves of green plants. It uses light energy to convert carbon dioxide and water into glucose. Oxygen is produced as a by-product of photosynthesis. ] by plants
- dissolving in the oceans.
Processes that return carbon dioxide from the air:
- respiration [respiration: Chemical change that takes place inside living cells, which uses glucose and oxygen to produce the energy organisms need to live. Carbon dioxide is a by-product of respiration ] by plants, animals and microbes
- combustion ie burning wood and fossil fuels such as coal, oil and gas
- thermal decomposition of limestone, for example, in the manufacture of iron, steel and cement.
All cells contain carbon, because they all contain proteins, fats and carbohydrates. For example, plant cell walls are made of cellulosecellulose: A carbohydrate. It forms the cell wall in plant cells., a carbohydrate.
Decomposers, such as microbes and fungi, play an important role in the carbon cycle. They break down the remains of dead plants and animals and, in doing so, release carbon dioxide through respiration.
For thousands of years, the processes in the carbon cycle were constant, so the percentage of carbon dioxide in the atmosphere did not change. Over the past 200 years, the percentage of carbon dioxide in the atmosphere has increased steadily because humans are:
- burning more and more fossil fuels as energy sources
- burning large areas of forests to clear land, which means that there is less photosynthesis removing carbon dioxide from the air.
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