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)
Attempt either (a) or (b) : (a) What will be the impact on an ecosystem if all the bacteria, fungi or microorganisms are removed from the environment ?
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(a) • Bacteria and fungi are decomposers that breakdown dead organisms or animal and plant wastes. If they are removed it will pollute the environment with dead remains, foul smell resulting in various diseases. (1) • Also, the nutrients present in the plants will not be recycled back into the environment. (1)
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)
Assertion (A): The energy transferred to a lion when it eats a deer is only a small fraction of the deer's total energy content. Reason (R): Energy transfer is efficient at all trophic levels with nearly 90% of energy passed on to the next level.
(a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
(b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
(c)Assertion (A) is true, but Reason (R) is false.
(d)Assertion (A) is false, but Reason (R) is true.
In a food chain, where plants are eaten by insects, insects are eaten by frog and frog is eaten by snake, if the energy available to the frog is $100\ \text{J}$, then the energy available to the insects and snake respectively will be :
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)
OR (b) Why do food chains in an ecosystem generally consist of only three or four steps?
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(b) Only 10% of energy passes from one trophic level to the next. The loss of energy at each step is so great that very little usable energy remains after four trophic levels. (2)
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?
(a) Improper waste disposal is a curse to the environment. Explain. (b) Why are crop fields considered as artificial ecosystems? (c) Farmers are using pesticides on the crop plants, but the chances of accumulation of harmful chemicals is greatest in human beings. Why? Name the phenomenon.
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(a) When waste is not segregated at source, it gets accumulated and materials like plastic will not be biodegraded. It may clog drains, pollute rivers and oceans and cause harm to cattle, fishes etc. (1) (Or any other) (b) Because crop fields are manmade ecosystem and in this living organisms interact with each other and also with the abiotic components of the ecosystem. (1) (c) These chemicals are non-biodegradable, hence keep getting accumulated at each trophic level, increasing progressively. As human beings occupy the top level in a food chain, the maximum concentration of these chemicals get accumulated in them. (½) Phenomena is Biological magnification. (½)
Consider a simple aquatic ecosystem like a lake which consists of algae, small fish and large fishes. It was found that the lake water was contaminated with a low concentration of a non-biodegradable pesticide, DDT. Based on this ecosystem, answer the following questions : (a) In which organism will the concentration of the pesticide DDT be the highest ? Name and explain the phenomenon. (b) Why is the flow of energy in a food chain always unidirectional ?
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• In large fishes (1 Mark) • Biological magnification: progressive accumulation of non-biodegradable harmful chemicals at each trophic level. (1 Mark) As energy flows progressively through the various trophic levels it is no longer available to the previous level / Energy available at each trophic level get diminished progressively due to loss of energy at each level. (1 Mark)
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.
Consider the following statements about ozone and choose the correct option : (i) One molecule of ozone gas is formed by three atoms of oxygen. (ii) Ozone is the product of UV radiations acting on oxygen ($\ce{O2}$) molecules. (iii) Ozone performs an essential function at the lower levels of the atmosphere. (iv) Ozone is very useful and is essential for all aerobic forms of life. Options :
(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)
How is ozone layer formed in our atmosphere ? State one important role of ozone in our atmosphere. What is responsible for its depletion ?
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$\bullet \quad \ce{O2 ->[UV] O + O}$ $\ce{O2 + O -> O3}$ (Ozone) (1) Alternate Answer $\bullet$ The higher energy UV radiations split apart some molecular oxygen (O2) into free oxygen atoms which then combine with the molecular Oxygen (O2) to form Ozone. (1) $\bullet$ Role: It prevents harmful UV rays to reach earth's atmosphere. ($\frac{1}{2}$) $\bullet$ CFCs (Chlorofluorocarbons) ($\frac{1}{2}$)
What role does UV radiation play in the formation of the ozone layer ? Explain the process with relevant chemical reactions. Why is the excessive use of CFCs (Chlorofluoro Carbons) is a cause of concern for organisms ?
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UV radiation split apart molecular oxygen into free oxygen atom necessary for ozone formation. (1 Mark) $\ce{O2 ->[UV] O + O}$ (1 Mark) $\ce{O + O2 -> O3}$ (ozone) (1 Mark) Excessive use of CFCs causes depletion of ozone layer. This allows more UV radiation entering the earth's atmosphere. That is highly damaging to organisms / cause skin cancer in humans. (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)
Give any two ways in which non-biodegradable substances would effect the environment adversely.
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(i) They persist in the environment for a long time and thus damage the environment. (1 Mark) (ii) They can cause soil, air and water pollution. (1 Mark) (any other ways) (2 Marks)
(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)
(a) Improper waste disposal is a curse to the environment. Explain. (b) Why are crop fields considered as artificial ecosystems ?
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(a) When waste is not segregated at source, it gets accumulated and materials like plastic will not be biodegraded. It may clog drains, pollute rivers and oceans and cause harm to cattle, fishes etc. (1) (Or any other) (b) Because crop fields are man-made ecosystem and in this living organisms interact with each other and also with the abiotic components of the ecosystem. (1) (c) These chemicals are non-biodegradable, hence keep getting accumulated at each trophic level, increasing progressively. As human beings occupy the top level in a food chain, the maximum concentration of these chemicals get accumulated in them. (1) Phenomena is Biological magnification. ($\frac{1}{2}$)
(A) If no decomposers in an ecosystem, what will happen to the garbage and dead animal and plant wastes. (B) As a student, what are the four changes in your daily habits you would adopt to reduce generation of non-biodegradable wastes ?
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(A) In absence of decomposers the complex organic substance present in the garbage, dead animals and plants wastes will not break down into simple substances and get accumulated. (1 Mark) (any other effect)