Saturday, 29 March 2014

CBSE Class 10th Science | Chapter 15. Our Environment | Solved Exercises

In Text Questions | Page 257 |Chapter 15. Our Environment | CBSE Class 10th Science

Question 1. Why are some substances biodegradable and some non-biodegradable?

Answer. Some substances can be acted upon by the micro organisms and broken down into simple substances. Such substances are called biodegradable.
Some substances are inert and cannot be acted upon by the microorganisms and do not breakdown into simple substances. Such substances are called non- biodegradable.


Question 2. Give any two ways in which biodegradable substances would affect the environment.

Answer. Biodegradable substances affect the environment in the following ways:
  1. These substances are decomposed by the action of microorganisms. This causes fowl smell.
  2. During the process of decaying of biodegradable substances, various types of gases are released which cause air pollution.


Question 3. Give any two ways in which non-biodegradable substances would affect the environment

Answer. The non-biodegradable substances affect the environment in the following ways:
  1. They persist in the environment for a long time and thus damage the environment.
  2. Such substances cause land pollution and water pollution.


Intext Questions |Page 261 |Chapter 15. Our Environment | CBSE Class 10th Science |

Question 1. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.

Answer. There are various series of organisms feeding on one another. These series of organisms taking part in various biotic levels form food chain. The steps or levels of the food chain are called trophic levels.
 There are various series of organisms feeding on one another. These series of organisms taking part in various biotic levels form food chain. The steps or levels of the food chain are called trophic levels.

The autotrophs or the producers are at the first trophic level. The herbivores or the primary consumers come at the second, small carnivores or the secondary consumers at the third and larger carnivores or the tertiary consumers form the fourth trophic level 

An example of food chain: Grass-->Deer-->Lion.
Various trophics levels:
  1. The grass , which is  autotroph or the producer, comes at the first trophic level . It fix up the solar energy and make it available for deer as primary consumer.
  2. Dear as a herbivore or  primary consumers of grass comes at  the second trophic level
  3. Lion, which is Top Carnivore, comes at Fourth trophic level. It consumes dear at second trophic level ( or others at  third trophic level).


Question 2. What is the role of decomposers in the ecosystem?.

Answer. Decomposers are called natural cleaning agent. They act on biodegradable substances and break them into simple substances. In this way, decomposers create a balance in the environment and play an important role in ecosystem.

Intext Questions | Page 264 |Chapter 15. Our Environment | CBSE Class 10th Science |

Question 1. What is ozone and how does it affect any ecosystem?

Answer. Ozone is a molecule formed by three atoms of oxygen. Ozone is formed by the reaction of three molecules of oxygen is presence of ultraviolet (UV) rays.
UV
3O2------>2O3

Ozone performs an essential function. It shields the surface of the earth from ultraviolet radiation of the sun If this radiation enters in the atmosphere, it could cause various disorders. So, ozone protects the ecosystem from damaging.

Question 2. How can you help in reducing the problem of waste disposal? Give any two methods.

Answer.
  1. There are two types of wastes; biodegradable and non-biodegradable. We should consume more and more substances that generate biodegradable wastes.
  2. Biodegradable wastes so generated, should be sent to solid waste management plants where it may be used either for compost production or making fuel bricks. Non-biodegradable waste should be segregated and then be sent to factories for recycling of products.


Solved Exercises  


Question 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

Answer. (c) Fruit-peels, cake and lime-juice (d) Cake, wood and grass.

Question 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

Answer. (b) Grass, goat and human.

Question 3. 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

Answer. (d) All of the above

Question 4. What will happen if we kill all the organisms in one trophic level?

Answer. Each and every trophic level depends for its energy needs on its previous trophic level. If all organisms of any of the trophic levels in a food chain are damaged, the organisms of other trophic levels will also be destroyed because energy flow is stopped from one trophic level to other trophic level.

The length and complexity of food chains vary greatly. Each organism at some irophic iLevel, is generally eaten by two or more other kinds of organisms of other tropic level. Which in turn are eaten by several other organisms. So instead of a straight line food chain, the relationship can be shown as a series of branching lines called a food web


Question 5. 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?

Answer. No, the impact of removing all the organisms in a trophic level is same for different trophic levels. The removal of organisms of any trophic level is damaging and it causes various disorder in ecosystem.

Question 6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?

Answer. When any harmful chemical like DDT enters in a food chain, its concen-tration increases gradually at each trophic level. This phenomenon is called biological magnification.
The levels of this magnification will be different at different levels of the ecosystem.

Question 7. What are the problems caused by the non-biodegradable wastes that we generate?

Answer. The non-biodegradable wastes persist in the environment for a long time and causes various problems.
Non-biodegradable wastes cause:
  1. Water pollution so that water becomes unfit for drinking.
  2. They cause land pollution and due to it land loses it beauty.
  3. They cause stoppage of flow of water in drains.
  4. They also cause air pollution and make the air poisonous.
Different compunds takes different time to biodegrade in a marine environment


Question 8. If all the waste we generate is biodegradable, will this have no impact on the environment?

Answer. The biodegradable wastes do not persist for a long time in the environment. However, they also cause harmful affects but these effects are only for sometime.These wastes can be converted into useful substances and broken into simple substances by the action of microorganism. So, there will be impact of biodegradable waste but for a short time.

Question 9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?

Answer. Enlargement of ozone hole will cause more ultraviolet rays to reach on the earth's surface. This is very harmful for us, animals and microorganisms in the following ways.
  1. Ultraviolet radiation may cause skin disease, especially skin cancer.
  2. plant life will be disturbed due to retarded growth and destruction of pigments.
  3. UV rays may kill microorganism, decomposers and other useful microbes. It may lead to ecological imbalance.

Steps to prevent damage of ozone layer:
  1. Judicious use of aerosol spray propellants such as fluorocarbon and chlorofluorocarbons which cause depletion or hole in ozone layer.
  2. Limited use of supersonic plains.
  3. Control over large scale nuclear explosions.


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Things to remember..
  • The various components of an ecosystem are interdependent.
  • Each step or level of the food chain forms a trophic level.
  • The producers make the energy from sunlight available to the rest of the ecosystem.
  • The autotrophs or the producers are at the first trophic level. They fix up the solar energy and make it available for heterotrophs or the consumers.
  • The herbivores or the primary consumers come at the second, small carnivores or the secondary consumers at the third and larger carnivores or the tertiary consumers form the fourth trophic level.
  • There is a loss of energy as we go from one trophic level to the next, this limits the number of trophic levels in a food-chain.
  • There are generally a greater number of individuals at the lower trophic levels of an ecosystem, the greatest number is of the producers.
  • Human activities have an impact on the environment.
  • The use of chemicals like CFCs has endangered the ozone layer. Since the ozone layer protects against the ultraviolet radiation from the Sun, this could damage the environment.
  • The waste we generate may be biodegradable or non-biodegradable.
  • The disposal of the waste we generate is causing serious environmental problems.
  • In nature, different materials biodegrade at different rates, and a number of factors are important in the rate of degradation of organic compounds. To be able to work effectively, most microorganisms that assist the biodegradation need light, water and oxygen. Temperature is also an important factor in determining the rate of biodegradation. This is because microorganisms tend to reproduce faster in warmer conditions. The rate of degradation of many soluble organic compounds is limited by bioavailability when the compounds have a strong affinity for surfaces in the environment
  • Different compounds takes different time to biodegrade in a marine environment.

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