Biology, 4g.

Things decay because of micro-organisms. Nearly all decomposition is done by soil bacteria and fungi. It happens everywhere in nature, compost heaps and sewage works. All the importantelements are therefore, recycled like, carbon, hydrogen, oxygen, and nitrogen. The rate of decay depends on 3 main things: 

1. Temperature. Warmth makes things decay faster, because it speeds up respiration in decomposers. 

2. Moisture. Things decay faster when they are moist, because decomposers need water. 

3. Oxygen. When oxygen is available, decaying is faster. The decomposers can respire aerobically, providing more energy. 

Decay is caused by decomposer's: bacteria; fungi. 

Detritivores such as earthworms, maggots and woodlice, feed on dead and decaying materials. They increase the rate of decay, because they produce a larger surface area. 

Saprophyte is a living bacteria, or fungi, that gain nitrogen form dead organisms. Decay involves saprophytic nutrition by bacteria and fungi. 

Micro-organisms are used to: break down human waste; break down plant waste. 

Food preservation techniques, reduce the rate of decay. 

1. Canning. Keeps decomposers out. After canning, the tin is heated to high temperature, to kill any bacteria already lurking. 

2. Cooling. Put it in the fridge. Slows down respiration in the micro-organisms. They can reproduce as fast either. 

3. Freezing. Can't respire or reproduce at all. Some are killed, when the water expands, a it freezes. 

4. Drying. Micro-organisms need water. Lots of fruits are dried out for preservation.

5. Adding salt. Loose water by osmosis, this damages them so they can't work properly. Tuna and olives are stored in salt water. 

6. Adding vinegar. Its acidic so it inhabits the enzymes inside the micro-organisms. Stops decomposition.