question_answer

Write notes on the following:

(i)  Food web

(ii) Xerarch

Answer:

(i)  Food web: Food chains are not strictly linear. They may have many branches that may link one food chain with another. The various interlinked food chains in a community constitute a food web.

There can be 3 types of food chains in a food web:

(a) Predator chains that begin with plants and proceed from small to large animals.

(b) Parasitic chains which proceed from large to small organisms.

(c) Saprophytic chains that proceed from dead animals to microorganisms.

(ii) Xerarch (succession on a barren rock): Lichens are pioneers on any barren rock. They secrete some acids which breakdown the rock Also, lichen thalli die and decompose forming a soil which is just good for the growth of mosses. So, lichens and mosses form a pioneer community. As further soil accumulation occurs, seeds of some herbs can gemmate in It As the litter and soil accumulates further, herbs give rise to shrubs. After the successful growth of shrubs "soil layer becomes deeper and gradually trees make their appearance. In a time of hundreds of years, a climax vegetation is reached which is in harmony with the environment.