Extra Questions for Class 12 Biology Chapter 14 Ecosystem
Q.1. What is detritus?
Ans. Dead organic matter or remains of plant such as leaves, bark, flower and dead remain of animals, including faecal matter constitute detritus.
Q.2. Why is the rate of assimilation of energy at the herbivore level called secondary productivity?
Ans. It is because the biomass available to the consumer for consumption is a resultant of the primary productivity from plants.
Q.3. Why is an earthworm called a detritivore?
Ans. This is because earthworm breaks down detritus into smaller particles.
Q.4. Name the basic requirement of any ecosystem to function and sustain properly.
Ans. A constant input of solar energy is the ultimate source of all energy and requirement of any ecosystem to function and sustain properly.
Q.5. Define mineralisation.
Ans. It is the process in which the humus is degraded by certain microbes and thus inorganic nutrients are released in the soil.
Q.6. What is secondary productivity?
Ans. Secondary productivity is defined as the rate of formation of new organic matter by consumers.
Q.7. What is net primary productivity?
Ans. The amount of energy or biomass remaining in a producer after meeting the cost of its respiration and is passed on to next trophic level is called the net primary productivity.
Q.8. All the primary productivity is not available to a herbivore. Give one reason.
Ans. All the primary productivity is not available to a herbivore because a considerable amount is utilised by the plant by respiration.
Q.9. Write the equation that helps in deriving the net primary productivity of an ecosystem.
Ans. GPP – R = NPP
Q.10. Write a difference between net primary productivity and gross productivity.
Ans. Gross productivity (GPP) is the rate of production of organic matter during photosynthesis. Net primary productivity (NPP) is the available biomass for the consumption by heterotrophs.
GPP − R = NPP
Q.11. Standing crop and biomass are related to each other, how?
Ans. The standing crop is measured as the mass of living organisms or the number of plants in a unit area. The biomass of a species is expressed in terms of fresh or dry weight.
Q. 10. List any two ways of measuring the standing crop of a trophic level.
Ans. Standing crop is measured as the biomass or the number of plant in a unit area.
Q.12. Define primary production.
Ans. It is defined as the amount of biomass or organic matter produced per unit area over a certain time period by plants during photosynthesis.
Q.13. What is meant by humification?
Ans. The process of formation of humus from detritus or dead organic matter is called humification.
Q.14. Differentiate between standing state and standing crop in an ecosystem.
Ans. In an ecosystem, standing crop is the mass of living material in each trophic level at a particular time. Whereas standing state refers to the amount of nutrients in the soil at any given time.
Q.15. Climax stage is achieved quickly in secondary succession as compared to primary succession. Why?
Ans. The rate of succession is much faster in secondary succession as the substratum (soil) is already present as compared to primary succession where the process starts from a bare area (rock).
Q.16. Arrange the following as you observe in vertical stratification of a forest—Grass, Shrubby plants, Teak, Amaranthus.
Ans. Grass, Amaranthus, Shrubby plants, Teak.
Q.17. Mention the role of pioneer species in primary succession on rocks.
Ans. The pioneer species invade a bare area and pave way for other species.
Q.18. Name the pioneer species:
(i) on a bare rock
(ii) in a water body
Ans. (i) Lichens
(ii) Phytoplanktons
Q.19. State what does ‘standing crop’ of a trophic level represent.
Ans. Standing crop represents the mass of living material (biomass) at a particular time.
Q.20. Under what conditions would a particular stage in the process of succession revert back to an earlier stage?
Ans. Natural or human induced disturbances like fire, deforestation, etc.
Q.21. What is a detritus food chain made up of? How do they meet their energy and nutritional requirements?
Ans. Dead plant and animal remains and their faecal matter constitute Detritus. DFC includes decomposers which obtain energy by decomposing the dead materials.
Q.22. Why is the pyramid of biomass inverted in a pond ecosystem?
Ans. The pyramid of biomass is inverted in a pond ecosystem because the biomass of fish (top consumer) is far larger than the producers (phytoplanktons).
Q.23. Why is a food web formed in nature?
Ans. Many organisms occupy positions in different food chains and several food chains become interconnected to form a food web.
Q.24. How is ‘stratification’ represented in a forest ecosystem?
Ans. Stratification in the vertical distribution of species at different levels. Trees occupy top vertical strata, shrubs the second layer and herbs/ grasses occupy the bottom layers.
Q.25. Name an omnivore which occurs in both grazing food chain and the decomposer food chain.
Ans. Sparrow/crow
Q.26. Why green plants are not found beyond a certain depth in the ocean?
Ans. Beyond a certain depth in the ocean, sunlight is not able to penetrate. Due to which green plants cannot photosynthesize and thus, do not survive.
Q.27. “Man can be a primary as well as a secondary consumer.” Justify this statement.
Ans. Man has a varied diet. When on vegetarian diet, they are primary consumers and when on nonvegetarian diet, they are secondary consumers.
