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Decay – Revision Pack (B4)
Decay:
Detritivores are organisms that feed on dead and decaying material (detritus) –
examples include woodlice, maggots and earthworms.
Detritivores increase the rate of decay by breaking up the detritus. This increases the
surface area for further microbial breakdown.
Rate of decay can also be increased by: increasing the temperature, amount of
oxygen and water.
Raising the temperature to 37oC will increase the rate of respiration for bacteria OR
raising it to 25oC will increase the rate of respiration for fungi.
If you increase the amount of oxygen, bacteria will use aerobic respiration to grow
and reproduce faster.
Increasing the amount of water will allow for material to be digested and absorbed
more easily and increase the growth and reproduction of fungi and bacteria.
A saprophyte is an organism that also feeds on dead and decaying material – an
example is fungus.
Saprophytes, like fungus, break material down in a few simple steps:
STEP 1 – The saprophyte produce enzymes
STEP 2 – These enzymes digest food outside their cells
STEP 3 – The saprophyte then reabsorbs the simple soluble substances
This type of digestion is called extracellular digestion.
Preserving Food:
In canning, the foods are heated to kill any
bacteria present and then sealed with a vacuum
to prevent the entry of oxygen and any microbes
like bacteria.
Cooling foods (in fridges for
example) slows down bacterial
and fungal growth and
reproduction.
Freezing foods (in freezers for
example) kills some bacteria and
fungi and slow their growth and
reproduction.
Decay – Revision Pack (B4)
Drying foods removes water so
bacteria cannot feed and
grow.
Adding vinegar will produce
very acidic conditions, thus
killing most bacteria and fungi.
Adding salt or sugar will kill some
bacteria and fungi – this is because the
high osmotic concentration will remove
water from them (meaning that they
cannot feed and grow).
Additional NOTES:
Decay will provide minerals for plants; for more information on this, see the ‘Plants
Need Minerals’ Revision Pack.
Decay – Revision Pack (B4)
Past Papers:
PPQ(1):
Decay – Revision Pack (B4)
PPQ(2):
TIP – Refer
to ‘Plants
need
Minerals’
Revision
Pack for
this
question
Decay – Revision Pack (B4)
PPQ(3):
PPQ(4):
Decay – Revision Pack (B4)
PPQ(5):
(Continued)
PPQ(6):
Decay – Revision Pack (B4)
Decay – Revision Pack (B4)
Mark Schemes:
PPQ(1):
PPQ(2):
PPQ(3):
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Decay – Revision Pack (B4)
PPQ(4):
PPQ(5):
PPQ(6):