]The key concept that we need to learn from food chains, food webs and food pyramids is the transfer of energy. For all life on earth there is only one available source of energy, the sun. Furthermore, only plants can change this energy into a form that can be used by animals. All plants rely either directly or indirectly on plants for their energy. Plants feed upon sunlight. Only plants have the ability to convert sunlight into food that they and animals can use.

Feeding levels are also called trophic levels. The word "trophic" is a Greek word for nourishment. To determine the trophic level, we count the number of energy transfers. Green plants are at the first trophic, or nourishment, level because there has been one transfer of energy, from the sun to the plants.

The first link in the chain, the plant, is called the produ

The various levels in the grazing food chain are linked to each other like links in a chain. The levels suggest a particular order for the passage of energy through the food chain. Like many very simple models, the idea of a food chain only provides a simple abstraction of the nature of energy flow through communities. The ultimate disposition of the energy assimilated by consumers is by four routes: respiration, biomass accumulation, decay of organic matter by bacteria and other decomposer organisms, and consumption by consumers.

Earthworms are one of the most important soil decomposers. These organisms consume vast amounts of organic matter and mineral soil. As the organic matter passes through their digestive system, it is subjected to digestive enzymes and the grinding action of mineral soil particles. The amount of material consumed per day is often equal to their body weight. Decomposers tend to always be active, processing large amounts of organic matter and releasing a great deal of energy mostly as heat from metabolic activities. Decomposers in most ecosystems process large amounts of organic matter, converting it back into its inorganic nutrient form.

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The actual amount of energy incorporated in the tissues of consumers at each tropic level is not determined by the gross amounts consumed. Rather it is the amount of organic energy converted into actual biomass. Consumers lose significant amounts of consumed energy due to assimilation inefficiencies, morphological and physiological maintenance, reproduction, and the process of finding and capturing food. The energy to perform the latter three processes is supplied by respiration.

cer, while all the links above it are called consumers. For example, look at a simple chain in which grass uses sunlight to produce sugars and proteins so it can grow. Rabbits eat the grass, and get energy from it. Foxes eat rabbits and get energy from them. Nothing eats foxes, so they are said to be at the top of that particular food chain. If something happens to the grass, suppose a farme

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