Biology

Ecosystem – Exemplar Solutions

Class 12 Biology Chapter 13 Exemplar Solutions

Multiple Choice Questions (MCQs)

1. Decomposers like fungi and bacteria are

(i) autotrophs

(ii) heterotrophs

(iii) saprotrophs

(iv) chemo-autotrophs

Choose the correct answer

(a) (i) and (iii)

(b) (i) and (iv)

(d) (i) and (ii)

2. The process of mineralisation by microorganisms helps in the release of

(a) inorganic nutrients from humus

(b) both organic and inorganic nutrients from detritus

(d) inorganic nutrients from detritus and formation of humus.

3. Productivity is the rate of production of biomass expressed in terms of

(i) (kcal m⁻³ ) yr⁻¹

(ii) g⁻² yr⁻¹

(iii) g⁻¹ yr⁻¹

(iv) (kcal m⁻² ) yr⁻¹

(a) (ii)

(b) (iii)

(d) (i) and (iii)

4. An inverted pyramid of biomass can be found in which ecosystem?

(a) Forest

(b) Marine

(d) Tundra

5. Which of the following is not a producer?

(a) Spirogyra

(b) Agaricus

(d) Nostoc

6. Which of the following ecosystems is most productive in terms of net primary production?

(a) Deserts

(b) Tropical rainforests

(d) Estuaries

Ans. (b) Tropical rain forests

7. Pyramid of numbers is

(a) Always upright

(b) Always inverted

(d) Neither upright nor inverted

8. Approximately how much of the solar energy that falls on the leaves of a plant is converted to chemical energy by photosynthesis?

(a) Less than 1%

(b) 2-10%

(d) 50%

9. Among the following, where do you think the process of decomposition would be the fastest?

(a) Tropical rain forest

(b) Antarctic

(d) Alpine region

10. How much of the net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores?

(a) 1%

(b) 10%

(d) 90%

11. During the process of ecological succession, the changes that take place in communities are

(a) orderly and sequential

(b) random

(b) very quick

(d) not influenced by the physical environment

12. Climax community is in a state of

(a) non-equilibrium

(b) equilibrium

(d) constant change

13. Among the following bio-geo-chemical cycles, which one does not have losses due to respiration?

(a) Phosphorus

(b) Nitrogen

(d) All of these

14. The sequence of communities of primary succession in water is

(a) Phytoplankton, sedges, free-floating hydrophytes, rooted hydrophytes, grasses, and trees.

(b) Phytoplankton, free-floating hydrophytes, rooted hydrophytes, sedges, grasses, and trees.

(d) Phytoplankton, rooted submerged hydrophytes, floating hydrophytes, reed swamp, sedges, meadow, and trees.

15. The reservoir for the gaseous type of bio-geochemical cycle exists in

(a) stratosphere

(b) atmosphere

(d) lithosphere

16. If the carbon atoms fixed by producers have already passed through three species, the trophic level of the last species would be

(a) scavenger

(b) tertiary producer

(d) secondary consumer

17. Which of the following types of ecosystem is expected in an area where evaporation exceeds precipitation, and mean annual rainfall is below 100mm

(a) Grassland

(b) Shrubby forest

(d) Mangrove

18. The zone at the edge of a lake or ocean, which is alternatively exposed to air and immersed in water, is called

(a) pelagic zone

(b) benthic zone

(d) littoral zone

19. Edaphic factor refers to

(a) water

(b) soil

(d) altitude

20. Which of the following is an ecosystem service provided by a natural ecosystem?

(a) Cycling of nutrients

(b) Prevention of soil erosion

(d) All of the above

Very Short Answer Type Questions

1. Name an organism found as secondary carnivore in an aquatic ecosystem.

2. What does the base tier of the ecological pyramid represent?

3. Under what conditions would a particular stage in the process of succession revert back to an earlier stage?

4. Arrange the following as observed in vertical stratification of a forest; Grass, Shrubby plants, Teak, Amaranths.

5. Name an omnivore which occurs in both grazing food chain and the decomposer food chain.

6. Justify the pitcher plant as a producer.

7. Name any two organisms which can occupy more than one trophic level in an ecosystem.

8. In the North East region of India, during the process of jhum cultivation, forests are cleared by burning and left for regrowth after a year of cultivation. How would you explain the regrowth of forest in ecological terms?

9. Climax stage is achieved quickly in secondary succession as compared to primary succession. Why?

10. Among bryophytes, lichens, and ferns, which one is a pioneer species in a xeric succession?

11. What is the ultimate source of energy for the ecosystems?

12. Is the common edible mushroom an autotroph or a heterotroph?

13. Why are oceans least productive?

14. Why is the rate of assimilation of energy at the herbivore level called secondary productivity?

15. Why are nutrient cycles in nature called biogeochemical cycles?

16. Give any two examples of xerarch succession.

17. Define self-sustainability.

18. Given below is a figure of an ecosystem. Answer the following questions.

(i) What type of ecosystem is shown in the figure?

(ii) Name any plant that is characteristic of such ecosystem.

19. What is common to earthworms, mushrooms, soil mites, and dung beetles in an ecosystem?

Short Answer Type Questions

1. Organisms at a higher trophic level have less energy available. Comment.

2. The number of trophic levels in an ecosystem are limited. Comment.

3. Is an aquarium a complete ecosystem?

4. What could be the reason for the faster rate of decomposition in the tropics?

5. Human activities interfere with carbon cycle. List any two such activities.

6. Flow of energy through various trophic levels in an ecosystem is unidirectional and non-cyclic. Explain.

7. Apart from plants and animals, microbes form a permanent biotic component in an ecosystem. While plants have been referred to as autotrophs and animals as heterotrophs. What are microbes referred to as? How do the microbes fulfill their energy requirements?

8. Poaching of tigers is a burning issue in today’s world. What implications would this activity have on the functioning of the ecosystem of which the tigers are an integral part?

9. In relation to energy transfer in ecosystem, explain the statement ‘‘10kg of deer’s meat is equivalent to 1 kg of lion’s flesh’’.

10. Primary productivity varies from ecosystem to ecosystem. Explain?

11. Sometimes, due to biotic/abiotic factors the climax remains in a particular seral stage (pre-climax) without reaching climax. Do you agree with this statement? If yes, give a suitable example.

12. What is an incomplete ecosystem? Explain with the help of suitable example.

13. What are the shortcomings of ecological pyramids in the study of ecosystems?

14. How do you distinguish between humification and mineralisation?

15. Fill in the trophic levels (1, 2, 3, and 4) in the boxes provided in the figure.

16. The rate of decomposition of detritus is affected by the abiotic factors like availability of oxygen, pH of the soil substratum, temperature, etc. Discuss.

Long Answer Type Questions

1. A farmer harvests his crop and expresses his harvest in three different ways.

(a) I have harvested 10 quintals of wheat.

(b) I have harvested 10 quintals of wheat today in one acre of land.

Do the above statements mean one and the same thing? If your answer is ‘yes’, give reasons. And if your answer is ‘no’, explain the meaning of each expression.

2. Justify the following statement in terms of ecosystem dynamics. “Nature tends to increase the gross primary productivity, while man tends to increase the net primary productivity”.

3. Which of the following ecosystems will be more productive in terms of primary productivity? Justify your answer. A young forest, a natural old forest, a shallow polluted lake, alpine meadow.

4. What are the three types of ecological pyramids? What information is conveyed by each pyramid with regard to structure, function, and energy in the ecosystem?

5. Write a short note on pyramid of numbers and pyramid of biomass.

6. Given below is a list of autotrophs and heterotrophs. With your knowledge about food chain, establish various linkages between the organisms on the principle of ‘eating and being eaten’. What is this inter-linkage established known as?

Algae, hydrilla, grasshopper, rat, squirrel, crow, maize plant, deer, rabbit, lizard, wolf, snake, peacock, phytoplankton, crustaceans, whale, tiger, lion, sparrow, duck, crane, cockroach, spider, toad, fish, leopard, elephant, goat, Nymphaea, Spirogyra.

7. “The energy flow in the ecosystem follows the second law of thermodynamics.” Explain.

8. What will happen to an ecosystem if

(a) All producers are removed

(b) All organisms of herbivore level are eliminated and

9. Give two examples of artificial or man-made ecosystems. List the salient features by which they differ from natural ecosystems.

10. The biodiversity increases when one moves from the pioneer to the climax stage. What could be the explanation?

11. What is a biogeochemical cycle? What is the role of the reservoir in a biogeochemical cycle? Give an example of a sedimentary cycle with reservoir located in Earth’s crust.

12. What will be the P/R ratio of a climax community and a pioneer community? What explanation could you offer for the changes seen in P/R ratio of a pioneer community and the climax community?

Class 12 Biology Chapter 13 Exemplar Solutions PDF

Here are the exemplar questions and answers for the chapter Ecosystem. You can download the PDF and thoroughly prepare for your exam. Click here to access the CBSE Class 12 Biology Chapter 13 Exemplar Solutions PDF.

Download Class 12 Biology Chapter 13 Exemplar Solutions PDF