<Li> Polysaccharides <Ol> <Li> cellulose </Li> <Li> hemicellulose </Li> <Li> starch </Li> <Li> pectin </Li> </Ol> </Li> <Ol> <Li> cellulose </Li> <Li> hemicellulose </Li> <Li> starch </Li> <Li> pectin </Li> </Ol> <P> Most living things in soils, including plants, insects, bacteria, and fungi, are dependent on organic matter for nutrients and / or energy . Soils have organic compounds in varying degrees of decomposition which rate is dependent on the temperature, soil moisture, and aeration . Bacteria and fungi feed on the raw organic matter, which are fed upon by amoebas, which in turn are fed upon by nematodes and arthropods . Organic matter holds soils open, allowing the infiltration of air and water, and may hold as much as twice its weight in water . Many soils, including desert and rocky - gravel soils, have little or no organic matter . Soils that are all organic matter, such as peat (histosols), are infertile . In its earliest stage of decomposition, the original organic material is often called raw organic matter . The final stage of decomposition is called humus . </P> <P> In grassland, much of the organic matter added to the soil is from the deep, fibrous, grass root systems . By contrast, tree leaves falling on the forest floor are the principal source of soil organic matter in the forest . Another difference is the frequent occurrence in the grasslands of fires that destroy large amounts of aboveground material but stimulate even greater contributions from roots . Also, the much greater acidity under any forests inhibits the action of certain soil organisms that otherwise would mix much of the surface litter into the mineral soil . As a result, the soils under grasslands generally develop a thicker A horizon with a deeper distribution of organic matter than in comparable soils under forests, which characteristically store most of their organic matter in the forest floor (O horizon) and thin A horizon . </P>

Describe briefly three things for which we are dependent on the soil