Organisms carbon dioxide from the air (photosynthesis)

Organisms of an ecosystem are linked together in food chains. A sheep may eat some grass, and in turn it may be eaten by a person. A mouse may eat some grain, and in turn it may be eaten by an owl, hawk, or fox. The algae of a lake will be eaten by many zooplanktons, such as crustaceans and insect larvae.

The latter are eaten by small fish, such as bluegills, and they in turn are eaten by bass, which may be caught by a bear. It becomes clear from all these cases that plants form the only link between the biotic and abiotic components of ecosystem.

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They draw water and minerals from the soil and combine them with sunlight and carbon dioxide from the air (photosynthesis) to make carbohydrates, fats, proteins, vitamins and usable minerals. Small herbivorous organisms, such as caterpillars, field mice, and copepods, consume this nutrient-rich vegetable matter and convert it to animal material.

They may then serve as food to support meat-eating animals, who may, in turn, be eaten by larger carnivores ; this sequence of eating and being eaten, with the resultant transfer of energy, is known as food chain.

All of these examples of food chains involve several links or steps and of course, there is energy dissipation along the way because of the inefficiency of the pro­cesses. Each step is known as trophic level and the study of energy flow through these steps is called trophic ecology.

Further, food chains are not isolated from One another. A mouse in a field may eat several types of seeds and be preyed upon by several different carnivores. Each of the carnivores may consume more than one type of prey and so on. Consequently, the food chains interlock with one another, and this inter-connecting network of species is spoken of as a food web.