Class 10 Science Chapter 13 Our Environment NCERT Notes

Chapter 13 Our Environment Class 10 Science CBSE NCERT Notes

Everything that surrounds us is environment. It includes both living (biotic) and non-living (abiotic) components.

An environment has four components: biosphere, atmosphere, hydrosphere and lithosphere

Eco System – What are its Components?

All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem.

An ecosystem is a self-sustaining, structural and functional unit of biosphere. It is an open system in terms of energy and a closed system as far as flow of minerals is concerned. A pond, lake, river, forest, desert, even a man-made aquarium and a crop field are examples of ecosystems.

An ecosystem consists of biotic components comprising of living organisms and abiotic components comprising of physical factors like temperature, rainfall, wind, soil and minerals.

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: It include all animals which depend on producers directly or indirectly for their food.

Consumers are further divided into:

Herbivores: Plant eaters for example, goat, deer.
Carnivores: Flash eaters for example, tiger, crocodile.
Omnivores: Eats both plants and animals for example, human.
Parasites: Live on the body of host and take food from it, for example, lice, cascuta.

Decomposers or saprophytes: It include organisms which decompose the dead plants and animals for example, bacteria, fungi. These help in the replenishment of natural resources.

Food Chains and Webs

Food chain is a series of organisms in which one organism eats another organism as food. The flow of energy in a food chain is unidirectional. A simple food chain operating in a grassland can be shown as:
Grass → Deer → Lion.

The various links or steps representing organisms in a food chain at which the transfer of food (and energy) takes place are called trophic levels.

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 lost as heat to the environment. Some amount goes into digestion and in doing work and the rest goes towards growth and reproduction.

An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers.

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

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

The network of interconnected food chains is called a food web.

Environmental problems

The sum total of all the factors that make our surroundings is called the environment. Human activities have damaged the balance of this environment leading to problems like global warming, soil erosion, floods, etc.

The environmental problems are pollution, soil erosion, deforestation, thinning of ozone layer, global warming, depletion of natural resources, extinction of plant and animal species, formation of salt deserts, waste accumulation, etc.

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

The high energy UV radiations break down the O, molecules into free oxygen (O) atoms.

These oxygen atoms then combine with oxygen (O2) molecule 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.

In 1987, the United Nations Environment Programme (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels.

Managing the Garbage we Produce

Improvements in lifestyle have resulted in accumulation of large amounts of waste materials.
Garbage contains following type of materials:

Biodegradable: Substances which can be decomposed by the action of micro-organisms are called biodegradable wastes. For example, fruit and vegetable peels, cotton, jute, dung, paper, etc.

Non-biodegradable wastes: Substances which cannot be decomposed by the action of micro-organisms are called non-biodegradable wastes. For example, plastic, polythene, 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

Most urban solid wastes can be burnt to make land fills.
Wastes like plastics, metals, etc., may be recycled.
Plastic wastes may be molten and mixed with asphalt to produce road making material.
Many domestic wastes like vegetable refuse can be composted and effectively used as manure.
Incineration: It is a waste treatment process that are described as thermal treatment, it converts the waste into ash mainly it is used to transforms medical wastes.