Our Environment sec_1

1. Environment : The physical, chemical and ‘ biological conditions of the region in which an organism lives is called its Environment. It includes air, light, soil, temperature, water and the presence or absence of other organisms, i.e., the conditions for development or growth.
Environment has three main components, viz :
(a) Physical surroundings [soil, air and water bodies]
(b) Living organisms [plants, animals, decomposers (bacteria and fungi)]
(c) Meteorological factors (or climatic factors) . [sunlight, temperature, rainfall, humidity, pressure and wind speed].

2. Physical environment: It is also called as abiotic or non-living environment. It includes :

1. Soil, water bodies and air on the surface of the earth.
2. Meteorological factors.

Physical environment is essential for :

(a) Supply of nutrient elements to the living beings.

(b) Providing space to the organisms for living.

(c) Controlling weather of a place.

3. Biotic (or biological) environment : It includes :

1. Plants.
2. Animals (including human beings).
3. Decomposers (bacteria and.fungi).

Other important constituent of biotic environment includes : Kites and vultures as they feed on dead organisms and act as scavengers (cleansing agents) of the environment.

4. Ecosystem : A community of organisms, interacting with each other, plus the environment in which they

live and with which they also interact. The examples of ecosystem are : a pond ; a desert; a forest; a lake ; a river ; a mountain ; the sea.

All the above ecosystems are made-up of two main components.

5. Autotrophs (Producers) and Heterotrophs (consumers):

6. Food chain: The sequence of living organisms in a . community in which one organism.e^ts other and is

itself eaten by another organism to transfer energy is called a food chain. It is also defined as, “chain of organisms, existing in any natural community, through which energy is transferred”.

7. Ozone layer : Ozone (O3) is a molecule formed by three atoms of oxygen unlike oxygen which is required for respiration by aerobic forms, ozone is a deadly poison. However, at the higher levels of the atmosphere,

ozone performs an essential function. It shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings.

Ozone at the higher levels of the atmosphere is a product of UV radiation, acting on oxygen (O2) molecule. The higher energy UV radiations split apart some molecular

oxygen (02) into free oxygen (O) atoms. These atoms then combine with the molecular oxygen to form ozone as shown:

Depletion of ozone layer: Ozone layer gets depleted – due to the use of chemicals called aerosol, spray propellants like chlorofluorocarbons. Depletion of ‘ ozone layer would cause skin cancer in men and animals and severe damage to the plants.

8. Biological magnification : It means accumulation of non-biodegradable chemicals (like pesticides) in the living organisms (like plants, animals, including man) in a food chain. “The increase in concentration of harmful chemicals in the body of living organisms at each trophic level of a food chain is called biological magnification”.

9. Biodegradable wastes and Non-biodegradable wastes:

10. A generalised food chain:

11. Food web: A food web is a network of food chains which establish a network of relationships between various species. Food web showing 8 interlinked food chains.

13. The flow of energy between various components of the environment:

1. Green plants capture about 1 % of the energy and convert it into food energy.
2. About f % of the food eaten is turned into the body of an organism and made available for the next level of consumers.
3. About 10% of organic matter is present at each step and reaches the next level of consumers.
4. Since so little energy is available for the next level of consumers, food chains generally consist of only three or four steps. The loss of energy at each step is so great that very little usable energy remains after four trophic levels.
5. There are generally a greater number of individuals at the lower trophic levels of an ecosystem, the greatest number is of the producers.