January 22, 2016

Junior Intermediate Imp Questions for 4 Marks - Botany Chapters 12-13

Q: Define plant succession. Differentiate primary and secondary successions.
A: The gradual change in the composition of species in a given area is called ecological succession.

Plant succession may occur through xerosere or hydrosere. When plant succession starts on a bare rock it is called xerosere. When it starts on an aquatic habitat it is called hydrosere.

The sequence of communities that successively change in a given area are called seres.
If the succession starts where no living organisms ever existed like bare rock it is
called primary succession.
Ex: Cooled lava, bare rock, newly created reservoir or pond. It takes long period to
reach a climax community in primary succession.

If the succession starts in an area where organisms were existing but somehow lost is
called secondary succession. Ex: Abandoned farm lands, burned forests, flooded lands. Climax community is reached in less time when compared to primary succession.

Q: Define ecosystem / ecological services. Explain in brief with regard to pollination.
A: Ecosystem services or ecological services are the services provided by nature that are life supporting and life enhancing.
Ecosystem service - pollination: Pollination is an essential part of healthy ecosystem.
It is the transfer of pollen grains from the anthers to the stigma of a flower to facilitate fertilization process.

In many plants pollination is carried out by different species of animals especially
insects. The pollination carried out through insects is called entamophily. The animals (insects) which carry out pollination are called pollinators.

They are very important to ensure fertilization and seed and fruit production in majority of our crop plants. Decline in pollinator activity results in loss of
crop yield. Nearly one lakh species of invertebrates and 1035 species of vertebrates act as pollinators. According to US Fish and Wildlife Service lists 50 pollinator species are threatened or endangered. Causes of decline in pollinators are deforestation and chemical pesticides.

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