Decay, Biology.

Decay is essential to our survival – it helps to digest food, and to recycle materials in our environment. Sometimes it can cause problems too, such as food spoilage (food going off).

The main groups of decomposer organisms are bacteria and fungi. Bacteria are single-celled microscopic organisms. Fungi are often larger organisms that include moulds and mushrooms. They both cause decay by releasing enzymes which break down compounds in their food so it can be absorbed by their cells. Organisms that feed on deadmaterial in this way are called saprophytes.

Speeding up decomposition

Decomposers such as bacteria and fungi cause decay at microscopic level. Other larger organisms help speed up decay by feeding on dead matter and breaking it down into smaller pieces, so increasing the surface area for the bacteria and fungi.

These larger organisms include earthworms that help break down dead leaves, woodlice that break down wood and maggots that feed on animal tissue. These larger organisms are detritivores.

Factor, Effect, Explanation.

Oxygen -  Lack of oxygen will slow or prevent most forms of decay -  Oxygen is needed for respiration by organisms. Some bacteria can survive without oxygen, such as those used in biogas generators.

Water -  Lack of water will slow or prevent decay -  Water is needed for transport and to support reactions inside organisms. Decay organisms need water to digest their food.

Temperature - High temperatures prevent decay, low temperatures slow decay -  High temperatures destroy enzymes and proteins, killing the organisms responsible for decay. Low temperatures slow the rate of reaction of enzymes and will prevent growth and reproduction.

MethodExamplesHow it works

Canning

Vegetables The sealed can is heated to kill bacteria. When it cools, no more bacteria can enter.

Cooling or chilling

Ready made meals The food is kept at a low temperature (4°C) so bacteria cannot reproduce (they're not killed).

Freezing

Vegetables and meat products Bacteria cannot reproduce at low temperatures and the water in the food is frozen.

Drying

Fruit, flour, soups, pasta Removing water prevents the microorganisms from growing, or digesting the food.

Adding salt or adding sugar

Jam, crisps, meat Removes water by osmosis

Adding vinegar

Pickles Changes the pH to prevent the enzymes in the microorganisms from working.