Food Chain:

As you know from the discussion of the previous subsection, one of  the ways in which the organisms are  related is through food, that is, one organism becomes food for  the other. A sequence of organisms  that feed on one another constitutes  a food chain.

The arrows in  the figure show the direction of passage of  nutrients and energy from the producer, a plant, to caterpillar,  to the sparrow and finally to the eagle. The number of  links or steps  in a food &.in  are usually limited to four or five. You may wonder why  it is so. You would find the answer to this later. Coming back to the links or steps in a food chain,  each of the link is also referred to as a trophic level. The  trophic leve!  to which an organism belongs, indicates how far it is away from plants in the food chain.

Green plants or producers make up the first  trophic level. The second trophic level contains  the plant eating animals,  the herbivores, and higher trophic levels are made up of carnivores. Another point, that we wish to make here is,  that an organism cannot always be assigned to one specific trophic level. Take  the example of man who is an omnivore,  i.e., he  is both a herbivore and a carnivore, so he may belong to the second and/or the third trophic level.