Question

Read the sources given and answer any four from the questions given below:

In a primary succession on a bare rock the first organisms often called pioneer organisms are lichens that invade the rocky area. The fungal component holds moisture and green algae provides food. The lichens form a crust over the bare rocks and begin to form soil from their organic remains and by stimulating chemical breakdown of the rocks. The erosion of rock, dead and decayed lichens provide sufficient soil for larger plant species to invade. Lichens are normally followed by mosses which grow in bunches and together with lichens, form a mat over the rock surface. This provides a suitable surface for the ferns and grasses to grow. Certain insects and small animals are also seen along with vegetation. Then the herbs, shrubs and trees replace the earlier vegetation and new animals continue to invade. Then dead shoots and fallen leaves enrich the soil. Ultimately these plants are succeeded by large seed-bearing plants which also support different kinds of animals. This final stable and selfgrowing community of trees is called as climax community. The changes in the biotic community from the pioneer to the climax community may take hundreds to thousands of years.

1. The pioneer organisms in a primary succession on a bare rock are
   1. fungi
   2. lichens
   3. grasses
   4. mosses
2. The community of tall trees and different types of animals on a bare rock can be seen after
   1. 10 years
   2. 100 years
   3. 200 years
   4. much more than 200 years
3. The sequence of communities on a bare rock is
   1. mosses-algae—lichens—fernstrees
   2. mosses-lichens—ferns—trees
   3. lichens—mossesferns—trees
   4. lichens—ferns—mosses—trees
4. In a primary succession, small animals and certain insects are usually seen when
   1. algae spread on rock
   2. lichens spread on rock
   3. ferns and grasses grow
   4. both (a) and (b)
5. In a primary succession, climax community is the one which is
   1. replaced by tall trees
   2. forms stable ecosystem
   3. gives rise to another primary succession
   4. both (b) and (c)

Answer 1

1. lichens
2. much more than 200 years
3. lichens—mossesferns—trees
4. ferns and grasses grow
5. forms stable ecosystem