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Q1. What is ecological succession? Distinguish primary succession from secondary succession.

Ans: The sequential, gradual and predictable changes in the species composition in an area are called succession or ecological succession.

Primary succession:

It begins in areas where no living organisms ever existed. Therefore, the establishment of a biotic community is very slow.

e.g., newly cooled lava, bare rock, newly created pond or reservoir.

Secondary succession:

It begins in areas where natural biotic communities have been destroyed.

e.g., abandoned farm lands, buried or cut forests. Since soil is available, it is a faster process.

Q2. Write a short note on ecosystem services.

Ans: The products of ecosystem processes are called ecosystem services.

Forests are the major source of ecosystem services. They

  • purify air and water,

  • cycle nutrients,

  • provide wildlife habitat,

  • pollinate crops,

  • mitigate droughts and flood,

  • generate fertile soils,

  • maintain biodiversity,

  • provide storage site for carbon,

  • provide aesthetic, cultural and spiritual values.

Q3. What is decomposition? Explain the steps of decomposition.


The process of breaking down complex organic matter into inorganic substances like C02, water and nutrient is called decomposition.

Steps in Decomposition:

Fragmentation: The process of breaking down of detritus into smaller particles is called fragmentation,

e.g., as done by earthworm.

Leaching: The process by which water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts is called leaching.

Catabolism: The enzymatic process by which degraded detritus is converted into simpler inorganic substances is called catabolism.

Humification: The process of accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate is called humification.

Mineralisation: The process by which humus is further degraded by some microbes to release inorganic nutrients is called mineralisation.

Q4. What is standing crop?

Ans: Each trophic level has a certain mass of living material at a particular time called the standing crop.

Q5. List the major functions of an ecosystem.


  1. Productivity

  2. Decomposition

  3. Energy flow

  4. Nutrient cycling

Q6. What is productivity? Mention their types.

Ans: The rate of biomass production per unit area, over a time period, by plant during photosynthesis is called productivity.

Productivity in an ecosystem is divided into gross primary productivity (GPP) and net primary productivity (NPP).

Q7. Explain the Primary succession in water.


  • The pioneer species are phytoplanktons.

  • The phytoplanktons are replaced by free-floating angiosperms.

  • Then, rooted angiosperms invade sedges, grasses and finally the trees.

  • At last, a stable climax forest is formed.

  • An aquatic habitat is converted into mesic habitat.

Q8. What is pioneer species?

Ans: The species that invade a bare area are called pioneer species.

Q9. Explain the phosphorous cycle with the help of schematic representation.


  • Rocks are the natural reservoirs of phosphorus.

  • During weathering of rocks, minute amounts of these phosphates dissolve in soil solution and are absorbed by plant through roots.

  • Herbivores and carnivores obtain this element from plants directly or indirectly.

  • The waste products and the dead organisms are decomposed by phosphate-solubilising bacteria and in turn release phosphorus.

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