Assertion (A): Natural replenishment of soil will not take place in absence of microbes. Reason (R) : Microbes, comprising of bacteria and fungi, break down dead remains and waste products of organisms, and they go into the soil.
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(A) / Both assertion (A) and reason (R) are true and Reason (R) is the correct explanation of Assertion (A)
What are decomposers ? List two important roles they play in the environment.
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• Decomposers are organisms that break down dead and decaying organic matter into simpler inorganic substances. (1 Mark) • Roles: ➢ Environment clean up (½ Mark) ➢ Nutrient recycling (½ Mark) (or any other relevant point)
Food chains, food webs, trophic levels, energy flow
Assertion (A): There are generally a greater number of individuals at the lower trophic levels of an ecosystem. Reason (R) : The greatest number is of the producers.
(a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
(b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
(c)Assertion (A) is true, but Reason (R) is false.
(d)Assertion (A) is false, but Reason (R) is true.
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(B) / Both Assertion (A) and Reason (R) are true but, Reason (R) is not the correct explanation of Assertion (A) (1 Mark)
In the following food chain, $5\ \text{J}$ of energy is available to man. Calculate, how much energy was available at the producer level. Why ? Plant $\longrightarrow$ Goat $\longrightarrow$ Man
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Plant $\rightarrow$ Goat $\rightarrow$ Man According to 10 % Law, only 10% of energy from a trophic level is transferred to the next trophic level. So, if Man has 5 J energy then Goat has $5 \times 10 = 50$ J And plants (producers) have $50 \times 10 = 500$ Joule
Describe why do food chains generally consist of a few steps.
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As only 10% of the total amount of organic matter of the food eaten at one trophic level, is made available for the next trophic level of consumers. Since the loss of energy at each step is so great that little energy is available for the next level of consumers, food chains generally consist of only three to four steps. (2 Marks)
In accumulation of toxic substances at higher trophic levels of an ecosystem through the food chain, which of the following organisms is affected the most?
Assertion (A) : Ozone at higher levels of atmosphere is a product of UV radiation acting on oxygen molecule. Reason (R): The higher energy of UV splits apart some molecular $\ce{O2}$.
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(A) / Both, Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A) 1 1
Assertion (A): Ozone ($\ce{O3}$) gas at higher levels of atmosphere is a product of UV radiation acting on Oxygen ($\ce{O2}$). Reason (R) : The amount of ozone in the atmosphere began to drop sharply in 1980s.
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(B)Both A and R are true but R is not the correct explanation of A.
(i) Chlorofluorocarbons (CFCs) have been linked to depletion of ozone layer. In 1987, the United Nations Environment Programme (UNEP) succeeded in making an agreement. State this agreement. (ii) What is the role of ozone in our atmosphere ?
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(i) To freeze the CFC production at 1986 levels. (1) (ii) Ozone shields the earth's surface from harmful UV radiations. (1)
(a) Explain the role of UV radiation in the formation of ozone layer. (b) Why is UV radiation considered as highly damaging to organisms ?
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(a) $\ce{O2 ->[uv] O + O}$ $\ce{O + O2 -> O3}$ / (Ozone) UV radiations split molecular oxygen into free oxygen and these atoms combine with oxygen to form ozone. (1 Mark) (b) It can cause diseases like skin cancer in human beings. (or any other harmful effect) (1 Mark)
Waste management; biodegradable vs non-biodegradable
Given below are some of the statements regarding our environment : (i) Change in our life-styles have resulted in greater amounts of waste material generation. (ii) Changes in attitude have resulted in use of more disposable things. (iii) Changes in packaging has resulted in much of our waste becoming non-biodegradable. (iv) Organic farming. Which amongst these is not leading to any damage of environment ?
The reasons for excessive generation of wastes are : (i) Use and throw policy. (ii) Increased availability of packaged food. (iii) Increased construction wastes. (iv) Non-sorting of dry and wet wastes. Options :
Suggest two ways of dealing with waste generated at home.
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• Kitchen wastes can be converted into manure/compost. • Newspapers, magazines, etc. can be recycled. • Metals/glass/plastic wastes can be recycled. (Any two ways or any other)
Suggest one precaution to be taken before disposing of the following : (a) Sewage from homes (b) Industrial wastes
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(a) Sewage should not contain solid waste, so sieve should be installed at the opening of drain. (or any other valid point) (1 Mark) (b) Chemical treatment of industrial waste should be done before disposing it off. (or any other valid point) (1 Mark)
(a) Mention any one harmful effect of using plastic bags on the environment. Suggest better alternatives to the usage of plastic bags. (b) Paddy fields require a large amount of water. The pesticides and chemical fertilizers used are washed down into the soil or waterbodies. How do these chemicals reach our bodies ? What is this phenomenon known as ?
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(a) • Plastics being non - biodegradable persist in environment for a long time. (any other harmful effect) (½ Mark) • Alternative - Jute or cloth bag (any other suitable alternative) (½ Mark) (b) • Pesticides and chemical fertilizers are not biodegradable. They accumulate progressively at each trophic level. As human beings occupy the top level in any food chain the maximum concentration of these chemicals get accumulated in our bodies. (1 Mark) • This Phenomenon is biological magnification. (1 Mark)