Most microorganisms that live in soil are detritivores, also known as saprovores or saprophages. Detritivores are organisms that eat detritus - decomposing organic matter.

Many detritivores only consume certain substances in a dead organism, rather than the whole body.

As they decay, organic substances in soil pass through a food chain, in which the most complex pieces of detritus are reduced to simpler and simpler substances.

For example, some detritivores consume cellulose, pectin and lignin- substances found in plant cell walls - from dead leaves that fall on top of soil.

They then leave simpler organic substances as waste, and other detritivores will consume this waste.

These detritivores will leave even simpler wastr products, such as sugars, which then will be used by another group of detritivores.

Food continues to pass downward through this food chain until eventually only inorganic materials - minerals, water and carbon dioxide - are left.

The many intermediate organic substances that are formed during this process affect the environment of the soil.

Many soil organisms create acids as waste products. These tend to accumulate in woodland soils, making woodland soil intolerable for many bacteria. However, fungi can tolerate acidic soil and therefore thrive in this type of soil.

Some microorganisms in soil produce antibiotics, which prevent competing organisms from growing. Some of these, such as Tetracycline and Streptomycin, have been used to fight bacterial infections in human beings.