Decay

GCSE BIOLOGY

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Decay is the process in which nutrients taken in by an organism during its lifetime is returned/recycled back
to the environment. If decay did not occur then e.g. dead animals would build up everywhere which would
cause a horrible scent and possibly increase spread of disease
Decay begins as soon as a plant/animal/organism dies Firstly detrius feeders (maggots, worms) feed on the
dead animal and as a result produce waste material. This helps to speed up decay as it helps break down
material into smaller pieces increaseing the surface area for microorganisms to work at.
Then decomposers come in which are bacteria and fungi. These are micro-organisms. They cause
decay by releasing enzymes which break down compounds in their food so it can be
absorbed by their cells. They digest everything from the dead animals/plants to the waste produced by
detrius feeders - turning it back into carbon dioxide, water and nitrogen containing minerals which are
replaced back into the soil producing fertile soil
Why is the decay process vital in the recycling of materials?
As it allows these materials to return to the environment to be taken in by other plants/animals. If decay did
not occur then these materials would not return to the environment and may run out.
What factors affect decay?
Temperature: Temperature needs to be just right so the decomposers enzymes can work at their
optimum and break down materials - if the temperature is too high then the decomposers enzymes will
denature and decay can no longer take place. If the temperature is too low then this slows down rate of
reaction of enzymes will prevent growth and reproduction.
Without oxygen decay would not be able to take place as oxygen is needed for aerobic respiration to
produce anergy for the decomposers to be able to break down materials.
Moisture/Water is needed for transport, support reactions inside organisms and to help decomposers
digest material.
Use of Decomposers in sewage treatment
1) Sewage enter mesh screens where large, insoluble objects e.g. Feaces, sock etc are removed.
2)The sewage then goes through a grit channel where even finer mesh is used to stop smaller things like
hair, sick from getting throgh.
3)This then enters a settling tank were it remains for days and the waste sludge rises.
4) This waste sludge then enters a tank of decomposers to decay/break down the waste anaerobically into
methane gas (which is used to drive pumps) The digested sludge is then dried out and sold as fertiliser.
5)The water is still not clean however, and so passes through a filter with holes at the side of it which allows
bacteria to take in oxygen and repire and break down remaining waste aerobically.
1) Now it either goes into to the river or is filtered again.
How are decomposers used in water treatment?
Decomposers are used to decay waste and break it down into carbon dioxide, water and minerals which
can be used as fertilers.

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Why are there holes in the filter tank?
As some decomposers e.g. Bacteria need oxygen in order to work. These holes provide oxygen for the
bacteria to respire aerobically and produce energy which can be used to break down remaining waste.
Why can the waste be used for fertilisers?
As decomposers can break down waste into minerals which are useful for plant growth.
Compost heap
When plant are growing they take in nutrients from the environment.…read more

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