15. OUR ENVIRONMENT
Questions:
1. List two man – made ecosystems.
Ans. Garden and pond are man – made ecosystems.
2. Name two decomposers operating in our ecosystem
Ans. Bacteria and Fungi.
3. Why do producers always occupy the first trophic level on every food chain?
Ans. Because producers (plants) have the ability to trap solar energy with the help of chlorophyll.
4. What will happen if we kill all the organisms in one trophic level?
Ans. If we kill all the organisms in one trophic level, the population of organisms in previous and next trophic level will increase.
5. What will be the amount of energy available to the organisms of the trophic level of a food chain, if the energy available at the first trophic level is 10,000 joules?
Ans. Only 10 percent energy is available from the first trophic level to second trophic level, i.e., 1,000 joules.
6. Why are some substances none – biodegradable?
Ans. Some substances are non – biodegradable because , they cannot be broken down into simpler harmless substance in nature.
7. The depletion of ozone layer is a cause of concern. Why?
Ans. Ultraviolet rays from the sun penetrate down the earth and cause health hazards/skin cancer in human being.
8. Why is excessive use of CFCs a cause of concern?
Ans. When CFC’S reach upper layers of the atmosphere, they cause depletion of ozone layer, and allow harmful ISV radiations to reach the surface of the earth to create health hazards.
9. The following organisms form a food chain. Which of these will have the highest concentration of non- biodegradable chemicals? Insects, Hawk, Grass, Snake, Frog. Name the phenomenon associated with it:
Ans. Hawk. Biomagnifications.
10. Which disease is caused in human beings due to depletion of ozone layer in the atmosphere?
Ans. Skin cancer is caused in human being due to depletion of ozone layer in the atmosphere.
11. Discuss the feeding patterns in a food web.
Ans. In a food web, each organism is generally eaten by two or more other kinds of organisms which in turn are eaten by several other organisms. So, a food web is a complex network of many interconnected food chains and feeding relationships.
12. Differentiate between the food habits of organisms belonging to first and second trophic levels.
Ans.
13. State with reason any two possible consequences of elimination of decomposers from the earth.
Ans. (i) The earth would be covered with dead organisms and their excrement as decomposers are recyclers of life materials, returning materials to the system for use by living organisms.
(ii) Elimination of decomposers would create an imbalance of nutrients as they break down complex organic material into simpler substances.
14. Write the appropriate names of the trophic levels Z and X in the figure given below:
Ans. Z — Tertiary consumers
X — Primary consumers
15. In the food chain:
Grass → deer → lion
Operating in a forest, what will happen if all the:
(i) lions are removed? - (ii) deers are removed?
Ans. (i) Number Of deer increases which will result in less amount of grass leading to soil erosion.
(ii) Food available for lions would be less. Amount of grassland will increase
16. What is Ozone ? How does it protect the organisms on the earth? OR What is ozone and how does it affect any ecosystem?
Ans. Ozone is a triatomic molecule of oxygen, (03). It forms a protective blanket over the earth’s , atmosphere and its depletion causes harmful effects on human. It absorbs the UV-radiation coming from the sun.
17. It is said, there is a need to put a blanket ban on the products containing aerosols.
What are aerosols ? Why is there a demand to put a ban on them?
Ans. An aerosol can be defined as a dispersion of solid and liquid particles suspended in gas. Atmospheric aerosols, unsurprisingly, refer to solid and liquid particles suspended in air. Aerosols are produced by dozens of different processes that occur on land and water surfaces, and in the atmosphere itself. There is a demand to put a ban on them because of their deteriorating effect on Earth’s ozone layer.
18. ‘Traditional use of forest areas is not useful in maintaining biodiversity. Do you agree with this statement? Explain with the help of an example.
Ans. The Great Himalayan National Park contains within its reserved area, alpine meadows which were grazed by sheep in summer. But now without regular grazing by sheep, the grass first grows very tall and then falls over, preventing fresh growth.
19. Why is Government of India imposing a ban on the use of polythene bags? Suggest two alternatives to use these bags and explain how this ban is likely to improve the environment. OR In some states of our country there is a ban on the use of polythene bags for shopping. Why? List there advantages of using jute or cloth bags over polythene bags.
Ans. Government of India is imposing a ban on the use of polythene bags because they cannot be degraded naturally by the action of microorganisms. Because of their non- biodegradability, they stay in the soil for a long time and continue to poison it with toxic by-products that keep leaching from them. Also, they do not allow water to seep in, as they are waterproof. These polythene bags, when accidentally eaten by stray animals, can harm them and can even lead to their death.
20. Give any two ways in which biodegradable substances would affect the environment.
Ans. (i) They produce foul smell during decomposition process.
(ii) They may produce harmful gases such as ammonia, methane and carbon dioxide.
21. What is meant by food chain? “The number of tropic levels in a food chain is limited.” Give reason to justify this statement.
Ans. Food chain is a simple representation of energy flow in nature. For example: A rat eats grains, a snake eats a rat, which in turn, is eaten by an eagle.
In a food chain, the number of trophic levels is limited to 4-5. This is because according to 10% law of energy transfer, only 10% of energy passes from one trophic level to next. Thus the amount of energy decreases with successive trophic levels. After five trophic levels6 existence of organisms would become impossible with such negligible amount of energy.
22. Explain the phenomenon of ‘Biological Magnification’. How does it affect organisms belonging to different trophic levels particularly the tertiary consumers?
Ans. Biological magnification refers to the process of increase in the concentration of a toxic chemical with increasing trophic level in a food chain. Harmful or poisonous substance such as DDT sprinkled to kill pests on plants enter the food chain. The plants absorb these harmful chemicals from soil along with water and minerals. They enter the food chain at producer level and then transfer to the next trophic level. The tertiary consumers get more higher levels of these chemicals.
23. Mention any three significance of a food chain.
Ans. Significance of a food chain:
(i) It helps in understanding the food relationship and interactions among various organisms in an ecosystem.
(ii) It helps in following the basic mechanism of transfer of food energy and nutrients through various components of nature.
(iii) It helps to understand the movement of toxic substances in an ecosystem and the problem of their biological magnification.
24. “Our food grains such as wheat and rice, the vegetables and fruits and even meat are found to contain varying amounts of pesticide residues.” State the reason to explain how and why it happens?
Ans. A large number of pesticides and chemicals are used to protect our crops from pests and diseases. Some of these chemicals are washed down into the soil, while some enter the water bodies. From the soil, they are absorbed by plants along with water and minerals; and from water bodies, they are taken up by aquatic plants and animals. This is how these chemicals enter the food chain. Because these chemicals cannot decompose, they accumulate progressively at each trophic level. As the food chain proceeds, the concentration of pesticides also increases. This increase in the concentration of harmful chemicals with each step of the food chain is called bio magnifications. That is why food grains, such as wheat and rice, vegetables, fruits and even meat are found to contain pesticide residue.
25. (i) What is the full form of: UNEP.
(ii) On what basis are organisms grouped as producers, consumers and decomposers?
(iii) Write two problems that would arise if there were no decomposers in an ecosystem.
Ans. (i) The full form of: UNEP is United Nations Environment Programmes.
(ii) Organisms can be grouped as producers, consumers and decomposers according to the manner in which they obtain their sustenance from the environment.
(iii) Two problems that would arise in absence of decomposers in an ecosystem are:
(a) Decomposition of garbage as well as dead plants and animals will not take place.
(b) Natural replenishment of soil will not take place.
26. Damage to the ozone layer is a cause for concern. Justify this statement. Suggest any two steps to limit this damage. OR
Ans. Due to ozone layer depletion, the ultraviolet rays reaches earth and causes certain ill-effects which are bad for us and for crops. Exposure to U-V rays can lead to greater incidence of skin cancer, cataracts and damages to the eye and immune deficiency. Two steps to limit this damage are:
(i) Minimizing the use of CFCs. CFC’s released into air accumulates in the upper atmosphere and reacts with ozone resulting in reduction in the thickness of the ozone layer.
(ii) In 1987, UNEP (United Nation Environment Programme) Succeeded in reaching an agreement to freeze CFC Production at 1986 levels.
27. When did the amount of Ozone in the atmosphere begin to drop sharply ? Why did this happen? How was this problem taken care of by UNEP?
Ans. The amount of Ozone in the atmosphere began to drop sharply in the 1980s. This decrease is due to the synthetic chemicals like chlorofluorocarbons which are used as refrigerants and in fire extinguishers. In 1987, United Nations Environment Programme, (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels.
28. Explain why the use of plastic bags are banned in many places? What could be more environment- friendly alternative?
Ans. Plastic is a non-biodegradable substance. Hence a plastic bag will persist in the environment and lead to several environmental problems. It would be better to use paper bags or cloth bags instead of polythene bags.
29. What are chlorofluorocarbon? How are they responsible for causing ozone hole in atmosphere? What will be the consequences of ozone hole?
Ans. Carbon compounds which contain chlorine and fluorine are called CFCs (chlorofluorocarbons). e.g., CCI2 F2 (Dichlorodifluoromethane). They lead to depletion of ozone layer causing ozone hole. Nitric oxide also reacts with ozone to form NO2 arid 02. CFCs (Chlorofluorocarbons) react with ozone in stratosphere and depletes ozone.
(i) It may lead to skin burns. (ii) It may cause skin cancer.
30. Give reasons: (i) Kulhads have been banned for serving tea on platform.
(ii) Decomposers are not included in any food chain.
(iii) Producers are transducers of energy
Ans. (i) As the top layer of soil is used up in making kulhads, it leads to infertility of the soil:
(ii) As decomposers, e.g., bacteria and fungi act on all trophic levels when the organisms occupying that level dies.
(ii) Producers are green plants, so they can convert solar energy into chemical energy in the form of food molecules.
Textbook Exercises:
1. Which of the following groups contain only biodegradable items?
(a) Grass, flowers and leather (b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice (d) Cake, wood and grass
Ans. (a), (c), (d)
2. Which of the following constitute a food-chain?
(a) Grass, wheat and mango (b) Grass, goat and human
(c) Goat cow and elephant (d) Grass, fish and goat
Ans. (b) Grass, goat and human
3. Which of the following are environment- friendly practices?
(a) Carrying cloth-bags
(b) To put purchases while shopping. Switching off unnecessary lights and fans
(c) Walking to school instead of getting your mother to drop you on her scooter.
(d) All of the above
Ans. (d) All of the above
4. What will happen if we kill all the organism in one trophic level?
Ans. If we kill all the organisms in one trophic level, then the next trophic levels will not get food to eat and the entire food chain gets disturbed,. At the same time the population of organisms at the lower trophic level will increase in abundance causing imbalance in nature.
5. Will the impact of removing all the organism in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Ans. Yes Removal of any organism will have different effect but it will cause an ill effect on the survival of that ecosystem.
6. What is biological magnification? Will the levels of this magnification be different at different levels of ecosystem?
Ans. The accumulation of harmful chemicals in the body of living organism at different trophic levels in a food chain is called biological’ magnification. Yes, the concentration of these harmful chemicals will be different at different trophic levels. It will be maximum at the last trophic level which is mostly the top carnivores.
7. What are the problems caused by the non- biodegradable wastes that we generate?
Ans. (i) Biological magnification
(ii) They cause bio magnifications and increase pollution
(iii) They make environment unclean
(iv) They kill useful micro – organisms, thereby reducing the fertility of soil.
8. If all the waste we generate is biodegradable, will this have no impact on the environment? Ans. Even the biodegradable wastes cause the environmental pollution. Accumulation of biodegradable wastes are responsible for:
(i) The excess of domestic sewage and nitrates from fertilizers cause excessive growth of phytoplankton’s called algal bloom, which in turn kills the aquatic animals.
(ii) The heaps of biodegradable solid wastes destroy the natural beauty of the landscape and make the surroundings unhygienic.
(iii) The decay and decomposition of such wastes produces foul gases and causes air pollution.
9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Ans. Refer Q-26 (Page No: 178)
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