Short Notes and Important Questions for Board Exams: Our Environment

Our Environment


• Everything that surrounds us is environment. It includes both living (biotic) and non-living (abiotic) components.
• Interaction between these biotic and abiotic components form an ecosystem.
• In an ecosystem living components depend on each other for their food which give rise to food chains and food webs in nature.
• Human activities lead to environmental problems such as depletion of ozone layer and production of huge amount of garbage.


All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem. E.g., forest, pond etc.
Types of ecosystem : It is of two types :
(a) Natural ecosystem : The ecosystem which exist in nature on its own. E.g., forest, lake, ocean.
(b) Artifical ecosystem : Man-made ecosystems are called artificial ecosystem. E.g., crop field, aquarium, garden.
Components of an ecosystem

(a) Abiotic Components : All the non-living components such as air, water, land, light, temperature etc. form the abiotic components.
(b) Biotic Components : All the living components such as plants, animals, bacteria, fungi etc. form the biotic components.

On the basis of nutrition biotic components are further divided into :
Producers : All green plants and blue-green algae can produce their own food using abiotic components (photosynthesis), hence called producers.
Consumers : Include all animals which depend on producers directly or indirectly for their food.
Consumers are further divided into :
(i) Herbivores : Plant eaters e.g., goat, deer.
(ii) Carnivores : Flash eaters e.g., tiger, crocodile.
(iii) Omnivores : Eats both plants and animals e.g., human.
(iv) Parasites: Live on the body of host and take food from it e.g., lice, cascuta.

Decomposers :

Include organisms which decompose the dead plants and animals e.g., bacteria, fungi. These help in the replenishment of natural resources.


• Food chain is a series of organisms in which one organism eats another organism as food. For e.g.,
Grass → Deer → Lion
• In a food chain various steps where transfer of energy takes place is called a trophic level.
Flow of energy between trophic levels
• Flow of energy in a food chain is unidirectional.
• Green plants capture 1% of sunlight and convert it into food energy.
10 percent law : Only 10% of energy is transferred to the next trophic level. The remaining 90% energy is used in life processes (digestion, growth, reproduction etc.) by present trophic level.

• Due to this gradual decrease in energy, food chains contain 3-4 trophic levels.



1 kJ
10 kJ
100 kJ
1000 kJ



Trophic levels Decrease in energy

Biological magnification : The concentration of harmful chemicals increases with every next trophic level in a food chain. This is called biological magnification.
• Maximum concentration of such chemicals get accumulated in human bodies as human occupy the top level in any food chain.
Food web : In nature large numbers of food chains are interconnected forming a food web.


Environmental problems : Changes in the environment affect us and our activities change the environment around us. Human activities leads to pollution, deforestation etc.

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Ozone layer

• Ozone layer is a protective blanket around the earth which absorbs most of the harmful UV (ultraviolet) radiations of the sunlight, thus protecting living beings from many health hazards such as skin cancer, cataract,
destruction of plants etc.
• Ozone (O3) layer is present at higher levels of atmosphere (i.e., stratosphere). It is a deadly poison at ground level.

Formation of ozone molecule

(i) The high energy UV radiation break down the O2 molecules into free oxygen (O) atoms

(ii) These oxygen atoms then combine with oxygen molecule (O2) to form the Ozone molecule

Depletion of ozone layer

• The decrease in the thickness of ozone layer over Antarctica was first observed in 1985 and was termed as ozone hole.
• This decrease was linked to excessive use of synthetic chemicals like chlorofluorocarbons (CFCs) which are used in refrigerators, ACs, fire-extinguishers, aerosols sprays etc.
• United Nations Environment Programme (UNEP) succeeded in forging an agreement to stop CFC production at 1986 levels (KYOTO PROTOCOL) by all countries.

Garbage disposal

Improvements in lifestyle have resulted in accumulation of large amounts of waste materials.
Garbage contains following type of materials :
(a) Biodegradable : Substances which can be decomposed by the action of micro-organisms are called biodegradable wastes.
E.g., fruit and vegetable peels, cotton, jute, dung, paper, etc.
(b) Non-biodegradable wastes : Substances which cannot be decomposed by the action of micro-organisms are called non-biodegradable wastes.
E.g., plastic, polythenes, metals, synthetic fibres, radioactive wastes,pesticides etc.
Micro-organisms release enzymes which decompose the materials but these enzymes are specific in their action that’s why enzymes cannot decompose all the materials.


Some methods of waste disposal

(a) Biogas plant : Biodegradable waste can be used in biogas plant to produce biogas and manure.

(b) Sewage treatment plant : The drain water can be cleaned in sewage treatment plant before adding it to rivers.

(c) Land fillings : The wastes are buried in low lying areas and are compacted by rolling with bulldozers.

(d) Composting : Organic wastes are filled in a compost pit and covered with a layer of soil, after about three months garbage changes to manure.
(e) Recycling : Non-biodegradable wastes are recycled to make new items.
(f) Reuse : It is a conventional technique to use an item again e.g., newspaper for making envelops.




1. Define trophic level.
2. What is the full form of CFC and UNEP ?
3. Name the radiations that are absorbed by the ozone layer.
4. Which will get more energy secondary consumers or tertiary consumers ?
5. What is the functional unit of environment ?
6. Which of the following are not biodegradable : Wool, glass, silver foil, leather.
7. Name any two parasites.
8. What is KYOTO protocol ?


1. Why are green plants called producers ?
2. Name two materials which can be recycled.
3. What will happen if we kill all the organisms of a trophic level ?
4. Why only 10% energy is transferred to the next trophic level ?

5. Which bag will you prefer for shopping and why ?
(a) Jute bag (b) Polythene bag
6. Why is ozone layer important for the existence of life on earth ?
7. What is the role of decomposers in ecosystem ?
8. Draw an energy pyramid showing different trophic level.


1. Differentiate between biodegradable waste and non-biodegradable waste.
2. How ozone molecule is formed in the atmosphere ?
3. Define consumers. What are its further divisions ?
4. Why natural ecosystem is more stable than artificial ecosystem ?
5. Why some materials are not decomposed by the action of micro-organisms ?
6. What is a food web ? Explain with example.
7. Give any two ways in which non-biodegradable wastes would affect the environment.
8. How the components of an ecosystem are dependent on each other ?


1. What are different methods for disposal of garbage ?
2. What is food chain ? Give its characteristics. Explain how energy flows through different trophic levels in a food chain.
3. Explain how harmful chemicals enter our body.

Hints to Long Answer Type Questions

1. Methods for Garbage disposal :
• Land filling
• Composting
• Recycling
• Reuse
• Biogas plant
• Sewage treatment plant

2. Food chain : Transfer of energy through various trophic level in an ecosystem.
Characteristics : (i) Unidirectional
(ii) 1% of total solar energy is absorbed by plants.
(iii) Transfer of energy through various trophic level is in accordance with 10 percent law.
3. Bio magnification

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