CLASS X SCIENCE / OUR ENVIRONMENT.

NOTES
OUR ENVIRONMENT

1.  Biodegradable substances can be further broken down by the action of bacteria e.g. � paper, vegetables, clothes etc. On the other hand the substances which can not be further broken down by the action of bacteria are non- biodegradable substances e.g. � plastics, glass etc.

2.  All biotic and abiotic components form the ecosystem. The biotic components are all living organisms. The non-biotic components are physical factors like air, water, soil, wind etc.

3.  The food chain consists of producers, consumers and decomposers. Green plants and algae that make food by photosynthesis are producers. Organisms that depend upon producers for their food, directly or indirectly are called consumers. And microorganisms like bacteria and fungi that break down the complex organic substances in dead plant and animal into simple inorganic substances are called decomposers.

4.  The series of organisms that take part in transferring food energy from producers to consumers to decomposers is called a food chain. Food chain link with each other to form food web.

5.  Every step of food chain is called a trophic level. There are four trophic levels

       I. I trophic level � producers/autotrophs

       II. II trophic level � primary consumers/herbivores

       III. III trophic level � secondary consumers/small carnivores

       IV. IV trophic level � tertiary consumers/large carnivores

6.  Green plants convert 1% of solar energy into food energy. The flow of energy is unidirectional.

7.  Ozone is present at a very high level in the atmosphere. It blocks the UV radiation of sun. Ozone is a product of UV radiation.

8.  At high level in the atmosphere the UV rays split the oxygen molecules to form oxygen atoms. These combine with oxygen molecules to form ozone. Ozone causes skin cancer, cataract and reduces crop production.

Class X Science
NCERT Solution for Our Environment

NCERT IN-TEXT QUESTIONS SOLVED

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

Ans. Substances which can be decomposed and broken down to simpler substances by micro-organisms acting on it is called bio-degradable and those substances which cannot be acted upon by microorganisms and are not broken down into simpler substances are called non-biodegradable substances.

2.  Give any two ways in which bio-degradable substances would affect the environment.

Ans. Two ways in which bio-degradable substances would affect the environment are:

      (i) During decomposition of the substances lot of foul smell spreads in the surrounding areas.

      (ii) The place where these bio-degradable substance are present with some moisture becomes breeding ground for insects like mosquitoes, housefly which are vectors in carrying parasites that cause different diseases.

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

Ans. (i) The non-biodegradable substances get accumulated and doesn��t get decomposed hence it remains in the ecosystem and causes pollution, chokes the system of many animals and kill them.

      (ii) These substances due to accumulation cause water and soil pollution e.g., pesticides, detergents, polythene.

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

Ans. The various levels or stages in a food chain at which the transfer of food takes place is called trophic level, e.g., food chain.

            Grass → Grasshopper → frog → snake → peacock

            Grass — Producer — trophic level.

            Grasshopper — I Consumer (Herbivores) — II trophic level’.

            Frog — II Consumer (Carnivores) — II trophic level

            Snake — III Consumer (Carnivores) — III trophic level

            Peacock — IV Consumer (Carnivores) — V trophic level.

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

Ans. Decomposers breakdown the complex organic substances like plant’s and animal’s dead body and convert them into simpler inorganic substances.

            All the elements that are present in the body on which decomposers act is released back to the nature. Decomposers maintain balance in the nature and plays an important role in the environment.

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

Ans. Ozone is a molecule of oxygen with 3 atoms its formula is O3. The ultra violet radiations split oxygen into free oxygen atoms, these atoms combine with oxygen molecules to form ozone.

           Ozone Ecosystem:

           At ground level ozone is poisonous but at higher level it is very useful as it protects all living organisms from harmful UV radiations of the sun. It doesn�t allow , the ultra violet radiations to enter the surface of earth. The UV radiations cause ionizing effect that leads,� to skin cancer in human beings.

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

Ans. To reduce the. problem of waste disposal we can

           (i) Segregate the. bio-degradable waste from non-biodegradable waste before dumping it.

           (ii) Remove all materials which can be recycled and send it for recycling. e.g., paper, glass, metal, rubber.

QUESTIONS FROM NCERT TEXTBOOK

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 (a), (c) and (d).

       (d) Cake, wood and grass

Ans. (a), (c) and (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 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. (d) All of the above

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

Ans. If all the organisms in one trophic level are killed then all the organisms of next trophic level which are dependent on these are killed. Next trophic levels will no!get food to eat and the entire food chain gets disturbed. At the same time thei�organisms at the lower trophic level will reproduce and the population will increase in abundance there by , disturbing the ecosystem.

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?

Ans. The impact of removing all the organisms in a trophic level will be same. If the organisms of any trophic level be removed it will certainly damage the ecosystem.

           For example,

           Grass → Grass hopper Frog → Snake → Peacock

           In this if all grasshoppers are killed/removed frogs will strive and grass will reproduce in abundance.

           If snakes are removed then the number of frogs will increase which will disturb the entire ecosystem.

6.  What is biological magnification? Will the levels pf this magnification ,bed different at different levels of the ecosystem?

Ans. The pesticides and chemicals are absorbed by plant from the soil and enter the food chain. Being non-biodegradable they accumulate progressively at, each trophic level. As human occupy the top level of any food chain, the maximum concentration of chemicals is found in our bodies. This is called biological magnification.

           The level of magnification will be different at different trophic levels, the maximum concentrations will be at the highest trophic level and the chemical will be less at lower trophic levels.

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

Ans. (i) As the non-biodegradable waste cannot be broken down into simpler forms hence they keep on accumulating ins nature causing pollution.

           (ii) They cause diseases.

           (iii) It also causes biological magnification.

8.  If all the waste we generate is bio-degradable, will this have no impact on the environment?

Ans. If all the waste we generate is bio-degradable and is managed in such a way that it is allowed to decompose then it will have no impact on the environment.

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

Ans. Ozone layer in the strastosphere is very helpful in shielding harmful UV rays. In absence of ozone layer heavy damage to organism may occur. It may cause diseases like skin cancer, cataract, reduced crop production etc.

           The damage is limited bye UNEP (United Nations Environment Programme), it has forged an agreement to freeze for CFC production in 1986.

           CFC– Chlorofluorocarbons used as refrigerants and in fire extinguishers.

MULTIPLE CHOICE QUESTIONS
OUR ENVIRONMENT

1.  Which of the following is a biodegradable substance?

       I.  Glass

      II.  Plants

     III.  Plastics

     IV.  Polythene

2.  Which of the following is a non-biodegradable substance?

       I.  Virgin plastic

      II.  Plastic

     III.  Plants

     IV.  Plant producers

3.  The constituents which do not form eco-system are

       I.  Biotic constituents

      II.  Plastic bags

     III.  Abiotic constituents

     IV.  All of these

4.  The functional unit of environment is

       I.  Ecosystem

      II.  Nitrogen

     III.  Carbon

     IV.  Oxygen

5.  Which of the following is an example of producers?

       I.  Plastic pens

      II.  Plastic cans

     III.  Polythene

     IV.  Green plants

6.  Which of the following is an example of herbivores?

       I.  Cow

      II.  Shark

     III.  Lion

     IV.  Tiger

7.  Which of the following is an not example of abiotic factors?

       I.  Light

      II.  Plants

     III.  Heat

     IV.  Temperature

8.  _______ is not a biodegradable pollutant.

       I.  Paper

      II.  Cotton cloth

     III.  Cotton

     IV.  DDT

9.  Which of the following is terrestrial ecosystem?

       I.  A natural forest

      II.  A lake

     III.  A pond

     IV.  An aquarium

10.  _______ is an omnivore animal.

       I.  Lion

      II.  Hawk

     III.  Jackal

     IV.  Man

11.  The formula of Ozone is _______

       I.  O3

      II.  O2

     III.  O4

     IV.  O6

12.  The number of atoms of oxygen present in ozone are

       I.  3

      II.  4

     III.  2

     IV.  1

ANSWERS

      1.   II

      2.   II

      3.   II

      4.   I

      5.   IV

      6.   I

      7.   II

      8.   IV

      9.   I

      10. IV

      11. I

      12. I

HIGH ORDER THINKING SKILLS
OUR ENVIRONMENT

1.  What is bad ozone?

2.  Differentiate between natural and artificial ecosystem.

3.  Why are plastic bags non-biodegradable?

4.  Name two decomposers and two producers.

5.  Why are pesticides considered as pollutants despite being useful to the farmers?

6.  Name two artificial eco-system.

7.  What is the role of consumers in the food chain?

8.  Give one advantage and one disadvantage of ozone.

9.  What is an ecosystem? Mention its components.

10.  Difference between biodegradable and non-biodegradable substance.

11.  Why are green plants called producers?

12.  What are the two main components of our environment?

          

Previous Year Questions
Our Environment

1.  Why are bacteria and fungi called decomposers? List any two advantages of decomposers to the environment.     (CBSE 2008)

2.  Distinguish between producers and decomposers. Classify the following as producers and decomposers: green plants, bacteria, fungi, blue-green algae.     (CBSE 2008 F)

3.  Why is the ozone layer getting depleted at the higher levels of the atmosphere?     (CBSE 2008)

4.  Name any two abiotic components of environment.     (CBSE 2009)

5.  What are the two main components of our environment?     (CBSE 2009)

6.  Which compounds are responsible for the depletion of ozone layer?     (AI CBSE 2009)

7.  Why are green plants called producers?     (AI CBSE 2009)

8.  Which disease is caused in human beings due to depletion of ozone layer?     (CBSE 2009 F)

9.  Distinguish between biodegradable and non-biodegradable substances.     (CBSE 2008)

10.  ï¿½Damage to ozone layer is a cause of concern�. Justify this statement and suggest two steps to limit this damage.     (CBSE 2008)

Test
Our Environment

Maximum time- 30 minutes

Maximum marks-25

1.  What are decomposers? Write their importance with respect to our environment.     (2)

2.  Write the causes of depletion of ozone layer. How can we prevent it?     (3)

3.  Explain the formation of ozone layer.     (2)

4.  Mention three information obtained from the energy flow diagram.     (3)

5.  What are food chains and food webs? Why are smaller food chains better?     (4)

6.  Energy flow in a food chain is unidirectional. Explain     (3)

7.  Give any three methods to reduce the problem of waste disposal.     (3)

8.  Differentiate between natural and artificial ecosystem.     (2)

9.  Write the full form of UNEP.     (1)

10.  Write the names of any two decomposers.     (2)