Page 8 - 2. Lesson notes-Food chain and Food web

Importance of food web

1. Food web does not allow any population to starve when members of lower trophic
level decrease in number.
2. Food web does not allow a population to overgrow as increased availability will
increase the chances of higher number of its predations.
3. Food webs provide stability to ecosystems.

Food Chain Food Web
1. It consists of a single unit of food It is a complex formed by several units of
relations. food relations.
2. It is a straight sequence of organisms. It is a network of many linkages among the
connected food chains.
3. It has a maximum of 4-6 populations of A food web consists of numerous
different species. populations of different species.
4. Only one type of organism is used as An organism can use two to several types of
food by a particular type of organisms. organisms as food.

5. A disturbance in food chain is difficult A disturbance is overcome after some time.
to overcome.

Flow of energy is always unidirectional

From the energy flow diagram, two things become clear. Firstly, the flow of energy is
unidirectional. The energy that is captured by the autotrophs does not revert back to the solar
input and the energy which passes to the herbivores does not come back to autotrophs. As it
moves progressively through the various trophic levels it is no longer available to the
previous level.

Biological magnification

Harmful chemicals like insecticides and pesticides which are used to protect crops from
insects and pests are absorbed by plants and enter the food chain. Since these chemicals
are non-biodegradable, they get accumulated at every trophic level and their concentration
increases. Since human beings occupy the highest trophic level, the concentration of these
harmful chemicals is maximum in our bodies.
The increase in concentration of harmful chemicals in the bodies of organisms at higher
trophic levels is called biological magnification.