Page 6 - 2. Lesson notes-Food chain and Food web

 When green plants are eaten by primary consumers, a great deal of energy is lost
as heat to the environment, some amount goes into digestion and in doing work and
the rest goes towards growth and reproduction.
 An average of 10% of the food eaten is turned into its own body and made available
for the next level of consumers.
 Therefore, 10% can be taken as the average value for the amount of organic matter
that is present at each step and reaches the next level of consumers.

Since so little energy is available for the next level of consumers, food chains
generally consist of only three or four steps. The loss of energy at each step is so great that
very little usable energy remains after four trophic levels.

There are generally a greater number of individuals at the lower trophic levels of an
ecosystem, the greatest number is of the producers.

The length and complexity of food chains vary greatly. Each organism is generally
eaten by two or more other kinds of organisms which, in turn, are eaten by several other
organisms. So instead of a straight line food chain, the relationship can be shown as a series
of branching lines called a food web.

Food web is a group of several interconnected food chains. In a food web an organism
gets food from more than one group of organisms.