CBSE Class 12 Biology Ecology Worksheet

Short Answer Type Questions

Question. Is an aquarium a complete ecosystem?
Answer : Aquarium is a man made ecosystem (artificial). If an ecosystem possess all physical and biological component, then it is said to be complete. Since aquarium has biotic (plants and fishes) and abiotic component (air, water) required for survival of fishes, so it is an complete ecosystem.

Question. What could be the reason for the faster rate of decomposition in the tropics?
Answer : Tropics are characterised by high temperature and moisture and soil is rich in humus and minerals. As the decomposition rate is regulated by climatic factors, thus optinum temperature and humidity enhance the activity of decomposrs while the dead remain is also available in rich amount, which supports the faster rate of decomposition in the tropics.

Question. Fill in the trophic levels (1, 2, 3 and 4) in the boxes provided in the figure.
Answer : (i) First trophic level (producers) - Plants (ii) Second trophic level (primary consumers) - Herbivores (iii) Third trophic level (secondary consumers) - Carnivores (iv) Fourth trophic level (tertiary consumers) - Top carnivores (Image 255)

Question. The rate of decomposition of detritus is affected by the abiotic factors like availability of oxygen, pH of the soil substratum, temperature etc. Discuss.
Answer : Decomposition of dead remain or matter of animal and plant is carried out by microorganisms like bacteria, fungi etc. The growth rate of these decomposers is affected by abiotic factors like temperature, humidity, pH of soil and light etc. The soil pH affect the composition of acidophilic and basophilic microorganisms. In absence or presence of oxygen aerobic and anaerobic processes occurs. In presence of oxygen, complete degradation of substance occureds while in absence of oxygen, there will be an incomplete degradation. Similarly, at high temperature microbes can not grow optimally but high or low temperature favours the growth of stress tolerant microorganisms.

Question. Human activities interfere with carbon cycle. List any two such activities.
Answer : Two human activities that interfere with carbon cycles are (i) Rapid deforestation and (ii) Massive burning of fossil fuel for energy and transport.

Question. Flow of energy through various trophic levels in an ecosystem is unidirectional and non-cyclic. Explain.
Answer : Flow of energy in an ecosystem is always unidirectional, i.e., energy flow in one way and is noncyclic, like (Image 253)

Question. 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?
Answer : On the basis of nutrition, organisms are classified as autotrophs and heterotrophs. Autotrophs are further categorised into photoautotrophs and chemoautotrophs, while heterotrophs may be parasite pred or a saprophyte etc. Microbes are saprotrophs and derive nourishment or energy from dead organic matter or remain of plants and animals and this digestion is extracellular.

Question. What are the shortcomings of ecological pyramids in the study of ecosystem?
Answer : Ecological pyramids are the graphical representation of ecological parameter. These are characterised by pyramid of number, pyramid of mass and pyramid of energy in an ecosystems. Assumption of a simple food chain is the major shortcoming of ecological pyramids. If we do not accomode food web, a clear position of or trophic levels of an organisms cannot be given. Saprophytic organism are not given any place in the ecological pyramid, though they are the important component in an ecosystem.

Long Answer Type Questions

Question. 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.
Answer : Primary Productivity can be defind as the rate at which primary producers (Green plants) traps and store solar radiation in form of biomass. This is measured in term of weight (g−2) and in term of energy (Kcal m −2) per year in given time. So, primary productivity varies from ecosystem to ecosystem and the ecosystem which possess more producer will be more productive in term of primary productivity. So young forest grow quicker than older, mature forest and are more productive in terms of productivity. The shallow polluted lake and alpins meadow will be less productive because of less number of producers and high amount of dead matter.

Question. 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.
Answer : Ecological Pyramids An ecological pyramid is a graphical representation of an ecological parameter as number of individual present in various trophic level of food chain. Properties of ecological pyramid (i) The trophic structure of an ecosystem is represented in the form of ecological pyramids. (ii) The base of each pyramid represents the producers or the first trophic level, while the apex represents tertiary or top level consumer. The three types of ecological pyramids are (a) Pyramid of number shows relationship between producers and consumers in an ecosystem in terms of numbers. It may be inverted or upright pyramid. (Image 257) Inverted pyramid of biomass. Small standing crop of phytoplankton supports large standing crop of zooplankton (c) Pyramid of energy is the relationship between producers and consumers in an ecosystem in terms of flow of energy. It is always upright because energy is always lost as heat at each step

Question. Write a short note on pyramid of numbers and pyramid of biomass.
Answer : Ecological pyramids are graphical representations of the relationship between organisms of different trophic levles that can be expressed in terms of number, biomass or energy. In most ecosystems, the pyramid of number is upright, i.e., producers are more in number than the herbivores and herbivores are more in number than the carnivores. But, the pyramid of number may be inverted as in a forest ecosystem, where the number of insects (primary consumers) are greater than the number of trees (producers). The pyramid of biomass is upright, generally, as the biomass of producers is more than biomass of herbivores and that of herbivores is more than biomass of carnivores. But, it is inverted in ecosystems like sea ecosystem, where the biomass of fishes (primary consumers) exceeds than phytoplankton (producers).

Question. 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.
Answer : Biogeochemical Cycle (i) The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling or biogeochemical cycles (Bio–living; geo–including air, water and rocks). (ii) Nutrient cycles are of two types (a) Gaseous (b) Sedimentary (iii) Atmosphere is the reservoir for gaseous type of nutrient cycle (e.g., nitrogen and carbon cycle). (iv) Earth’s crust is the reservoir of sedimentary cycle (e.g., sulphur and phosphorus cycle). (v) The function of the reservoir is to meet with the deficit, which occurs due to imbalance in the rate of influx and efflux. (vi) Environmental factors, e.g., soil, moisture, pH, temperature, etc., regulate the rate of release of nutrients into the atmosphere. Phosphorus Cycle Phosphorus cycle is an example of sedimentary nutrient cycle since, it moves from land and sedimented at the bottom of the seas, then back to land again. The natural reservoir of phosphorus is earth’s crust. Rock contains phosphorus in the form of phosphates. By weathering and soil erosion, phosphates enter streams, rivers and then to oceAnswer : With great movements of the crustal plates, sea floor is uplifted and phosphates become exposed on the drained land surfaces. From here, weathering over long periods of time releases phosphates. From rocks, minute amount of these phosphates dissolve in soil and are absorbed by the roots of the plants. Herbivores and other animals obtain this element from plants when they consume plants as their food. The waste products and the dead organisms are decomposed by phosphate-solubilising bacteria thus releasing phosphorus.

Question. 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?
Answer : Production/Respiration ratio (P/R) ratio It shows the relationship between gross production and total community respiration where P/R=1 a steady state community result. This result may be instantaneously daily one or over a longer period. If P/R is persistantly greater or less than/then organic matter either accumulates or is depleted respectively.

Question. 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.
Answer : Food Chain and Food Web A straight line sequence of ‘who eats whom’ or eating and being eaten in an ecosystem is called a food chain. A network of cross connecting food chains involving producers, consumers and decomposers are termed as a food web. Lion, Tiger — Top carnivore (Top tropic level) Spider, cockroach, lizard, wolf, snake, toad, fish, crane — Secondry Consumer (IIIrd trophic level). Crustaceans, grasshopper, deer, mouse, squirrel, rabbit, elephant, goat — Primary Consumer (IInd trophic level). Phytoplankton, algae, Hydrilla, maize plant, Nymphaea, Spirogyra — Producers (Ist trophic level).

1. In a pond there were 40 lotus plants. After a year the number increased to 56. Calculate birth rate of a lotus plant. 1

2. Why pyramid of energy can never be inverted? 1

3. Why do cattle avoid browsing on Calotropis plants? 1

4. What is Allen’s rule? 1

5. Lichen is considered a good example of obligate mutualism. Explain. 1

6. Distinguish between primary productivity and secondary productivity 2

7. Write the differences between the seral stage and the climax community during succession. 2

8. What measures can be adopted in surroundings to decrease the noise pollution? 2

9. What are the advantages of ‘Ecosan’ ? 2

10. Giving two reasons explain why there is more species biodiversity in tropical latitudes than in temperate ones. 2

11. Mention the major cause of air pollution in metro cities. Write any three ways by which it can be reduced. 2

12. Name the four functional aspects of an ecosystem.

13. What steps have been taken by the Government to reduce pollution in Delhi?

14. What is the condition to dispose off the radioactive waste? 3

15. Describe the process of succession on a bare rock. 3

16. What function do detritivores play in an ecosystem? Explain the significance of humification and mineralization in a decomposition cycle.