Our Environment Class 10 Notes Science Chapter 15


1. Introduction

(i) The environment includes our physical surroundings like air (or atmosphere), water bodies, soil (land) and all the organisms such as plants, animals, human beings and micro-organisms like bacteria and fungi (called decomposers).

(ii) The disposal of waste should be done in a scientific way. There are different methods of waste disposal. The method to be used depends on the nature of the waste. Some of the important modes of waste disposal are:
(a) Recycling (b) Preparation of compost
(c) Incineration (d) Landfill
(e) Sewage treatment

2. Classification of waste:

The waste materials produced by the various activities of man and animals are poisonous to some extent and can be divided into two main groups :

(i) Biodegradable waste: It is a type of waste, typically originating from plant or animal sources, which may be degraded by other living organisms, e.g., wood, paper, natural products etc.
(ii) Non-biodegradable waste: It is a type of waste, which remains in the environment without getting decomposed by any natural agents and also causing harm to the environment.
e.g., metals, plastics, polybags etc.

3. Ecosystem:

An ecosystem is a self-contained unit of living things (plants, animals and decomposers), and their non-living environment (soil, air and water). e.g. a forest, a pond, a lake, a greenland etc.

4. Components of ecosystem:

There are two components of an ecosystem:
(i) Biotic component: Biotic components are the living things that shape an ecosystem, e.g., plants, animals etc. It includes the following types of organisms:

  • (a) Producer: Producers are either a green plant or bacterium, which is a part of the first level of a food chain.
  • (b) Consumer: Consumers are organisms of an ecological food chain which receive energy by consuming other organisms, e.g., heterotrophs which include animal, fungi and bacteria.
  • (c) Decomposer/saprophyte: The micro-organisms which break down the complex organic compounds present in dead organisms like dead plants and animals and their products like faeces, urine, etc. into simpler substances are called decomposers.

(ii) Abiotic component: They are non-living chemical or physical parts of the environment that affect living organism and functioning of ecosystem, e.g., air, temperature etc.

5. Planktons:

Planktons are very minute or microscopic organisms, freely floating on the surface of water in a pond, lake, river or ocean. Planktons are of two types:
(a) Phytoplanktons: The microscopic aquatic plants freely floating on the surface of water are called phytoplanktons.
(b) Zooplanktons: The microscopic aquatic animals freely floating on water are called zooplanktons. The freely-floating protozoa are an example of zooplankton.

6. Food chain and Food web:

(i) Food chain: The sequence of living organisms in a community in which one organism consumes another organism to transfer food energy is called a food chain.

  • A food chain is unidirectional where transfer of energy takes place in only one direction.
  • In aquatic ecosystem of the biosphere, like fresh water ponds, lakes or sea, the food chain starts with microscopic free floating plants (phytoplankton)
  • The various steps in a food chain at which the transfer of food (or energy) takes place are called trophic levels.

(ii) Food web: The inter-connected food chains operating in an ecosystem which establish a network of relationships between various species, is called a food web.
(iii) Ten percent law: Ten percent law states that only 10 percent of the energy entering a particular trophic level of organisms is available for transfer to the next higher trophic level.
(iv) Biological magnification: The increase in concentration of harmful
chemical substances like pesticides, in the body of living organisms at each trophic level of a food chain is called biological magnification.

7. How do our activities affect the environment?
(i) Global warming: The addition of certain pollutants like the carbon dioxide gases increases the temperature of the earth. The reduction in the forest cover also contributes to the heating of earth. This is called global warming.
(ii) Ozone layer formation and its importance:
(a) Ozone forms a kind of layer in the stratoshpere, where it is more concentrated than anywhere else. It is formed by three atoms of oxygen. Ozone, is a deadly poison. Ozone and oxygen molecules in the stratosphere absorb ultraviolet light from the sun, providing a shield that prevents radiation from passing to the Earth’s surface.
(b) Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (02) molecule. The higher energy UV
radiations split apart some molecular oxygen (02) into free oxygen (O)atoms.
(c) The depletion of ozone layer is due to CFCs (chlorofluorocarbons).
(d) The ozone layer absorbs the harmful UV radiations and presents it to reach the earth’s surface.
(e) Apart from that the ozone layer present in the lower atmosphere also absorbs different pollutants from the air.

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