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Chapter Review:

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• Substances that are broken down by the biological processes are said to be biodegradable.
• Substances that are not broken down by biological processes are said to be non-biodegradable.
• Ecosystem is a structural and functional unit of the biosphere consisting of a community of living beings and the physical environment; both interacting exchanging materials between them.
• The abiotic component of an ecosystem is a community of Physical environment.
• The biotic component of an ecosystem is a community of living organisms.
• These are the organisms which are able to systhesise their food. They are mainly green plants.Therefore, all green plants are called producers. They are also called autotrophs.
• They are organisms which consume other organisms or their products as their food. The consumers depend upon producers for their food directly or indirectly. They get their food either by eating other organisms or their products.
• These are organisms (animals) which get their food by eating the
  producers (or plants) directly. Herbivores are also called first order
  consumers.
• These are organisms (animals) which consume other animals.
  Therefore, carnivores feed on the flesh of harbivores. These are also called primary carnivores or second order consumers.
• The organisms which feed on both plants and animals are called
  omnivores.
• Which break down the complex organic compounds present in dead organisms like plants and their products into a simpler substance. These are called reducers.
• The network of various food chains which are interconnected at various tropic levels is called food web.
• One organism consumes another organism to transfer food energy is called a food chain. In a food chain, unidirectional transfer of energy takes place.
• Energy is used and conveyed from one trophic level to another is a food chain. This is called flow of energy.
• According to ten percent law only ten percent of the energy entering a particular trophic level is stored and the remaining is lost during energy transfer.
• Chemicals like DDT are widely used to kill pests.

Text-book Questions

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Page no. 257 

Q1. Why are some substances biodegradable and some non-biodegradable?

Ans: Non-biodegradable substances are those which are decomposed by small organisms into simpler substances in a biological process. In contrast, non-biodegradable substances remain for a long time. They do not know how to decompose and they are harmful.

Q2. Give any two ways in which biodegradable substances would affect the environment.

Ans: (i) The decomposition of organic matter makes the atmosphere smelly.

(ii) Some toxic gases are produced during their decomposition such as - CO₂, it pollutes the environment.

Q3. Give any two ways in which non-biodegradable substances would affect the environment.

Ans: (i) Non-biodegradable substances remain in the environment for a long time due to not being decomposed, hence polluting the environment.

(ii) They are spreading dirt on the earth. These are also affecting the sewerage system. Example - plastic bags.

Page no. 261

Q1. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.

Ans: The chain of organisms participating at various biological levels forms the food chain.

Each of its stages forms a trophic level.

Grass - worm - frog - snake - vulture

(a) Grass is the first trophic level of the food chain. It prepares its own food.

(b) The worm is the second trophic level of the food chain.

(c) Frog is the third trophic level and it eats grass.

(d) Snake is the fourth host of this chain.

(e) Vulture is the fifth and end host level of this chain.

Q2. What is the role of decomposers in the ecosystem?

Ans: Micro-organisms like bacteria and fungi etc. scavenge the residue. These organisms convert complex organic substances into simple inorganic substances. These substances are absorbed by the soil, so these micro-organisms help in recycling and protect the environment from dirt.

Page no. 264 

Q1. What is ozone and how does it affect any ecosystem?

Ans: Three atoms of oxygen combine to form one molecule of ozone O3. The ozone layer is in the upper surface of the atmosphere, it absorbs the harmful ultraviolet radiations of the sun. Therefore, ozone protects us from many diseases like skin cancer, ulcers etc.

Q2. How can you help in reducing the problem of waste disposal? Give any two methods.

Ans: (i) We should use organic matter instead of inorganic material. We should use paper or jute bags instead of plastic bags.

(ii) Organic waste should be disposed of in a place where it can be ready for recycling.

NCERT Solutions Exercise

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Q1. 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. Grass, wood and plastic.

Q2. 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. Grass, goat and human.

Q3. Which of the following are environment-friendly practices?

(a) Carrying cloth-bags to put purchases in while shopping.

(b) 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. All of the above.

Q4. 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 transfer of food energy tothe next trophic level will stop this will cause a break in the food chain resulting in esosystem imbalance.

Q5. Will the impact of removing all the organisms 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, the impact of removing all the arganisms in a trophic level be different for different trophic levels. If all the produced are killed. If will cause death or migration of the primary consumers in the ecosystem. 

Q6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?

Ans. Progressive increase in the concentration of non-biodegradable substance in a food chain is called biological magnification. The level of these harmful substence will go on increasing food onne trophic level.

Q7. What are the problems caused by the non-biodegradable wastes that we generate?

Ans: The non-biodegradable waste produced by us pollutes the environment. They do not decompose. Hence the problem of on-key disposal also comes. This creates many problems.

(i) Decrease the members of the ecosystem.

(ii) increase the biomagnification by creating it.

(iii) Water, land and air pollute.

Q8. If all the waste we generate is biodegradable, will this have no impact on the environment?

Ans: Biodegradable waste pollutes the environment only for a limited period of time. After this, it gets destroyed when it is destroyed and is also useful in recycling. After their decomposition, odor and toxic gases are generated in the atmosphere.

Q9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?

Ans: The ozone layer O3 protects us from the harmful ultraviolet radiations of the sun. Due to its damage, it causes skin diseases and skin cancer by reaching the radiations to the earth. So this is a matter of concern for us. Chlorofluorocarbons, which are used in refrigerators and fire extinguishers, are damaging ozone. To limit this damage, we should minimize the use of chlorofluorocarbons and chemical substances. 

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