Class 9 Science

Natural Resources

Resources which are obtained from nature are called natural resources. Examples: Air, water, soil, wood, etc.


The sum of all ecosystems on the earth is called biosphere. Biosphere is the narrow zone where atmosphere, hydrosphere and lithosphere meet.

In terms of flow of matter, biosphere is a closed system. This means there is minimal flow of matter in biosphere.

In terms of flow of energy, biosphere is an open system. This means the flow of energy is optimum in biosphere. The flow energy in biosphere begins with photosynthesis.

Biotic Components: Living things constitute the biotic component of the biosphere.

Abiotic Components: The air, the water and the soil form the non-living or a biotic component of the biosphere. The air is called the atmosphere, the water is hydrosphere and the soil is called lithosphere.


Air is a mixture of many gases like nitrogen, oxygen, carbon dioxide and water vapour.

Role of the Atmosphere in Climate Control

Atmosphere covers the Earth, like a blanket. We know that air is a bad conductor of heat. Thus, air prevents the earth from becoming too hot. Air also prevents solar radiation from escaping the earth. Thus, it prevents the earth from becoming too cold during night.

Wind: The Moving Air

Earth’s surface gets different amount of heat from the sun at different places. This causes uneven heating of the earth’s surface. Heating of the earth’s surface creates convection currents in air. Convection currents cause movement of air.

Earth's surface near the equator heats up more than on higher latitudes. This causes warm air near equator move upwards. After that, cooler air from surrounding latitudes move towards the equator. This initiates the process of wind movement on earth.

Air Pollution

Addition of harmful substances in air so that the air becomes unfit for living beings is called air pollution.

Primary Pollutant

If a pollutant is directly emitted from a process, it is called a primary pollutant. Examples; carbon dioxide from vehicle exhaust, ash from volcano, etc.

Secondary Pollutant

If a pollutant if formed after interaction or reaction of primary pollutants, it is called secondary pollutant. Example: ground level ozone, smog, etc.


Heating of water bodies during the day causes evaporation of water. Water vapor rises in the air. Once the water vapor goes up to a height, it cools down to form clouds. Formation of clouds is facilitated by some particles which act as the ‘nucleus’ around which water droplets coalesce to make cloud. Further condensation of vapor results in precipitation.


Importance of Water

All cellular processes take place in a water medium. All the reactions that take place within our body and within the cells occur between substances that are dissolved in water. Substances are also transported from one part of the body to the other in a dissolved form. Hence, organisms need to maintain the level of water within their bodies in order to stay alive.

Water Pollution

Contamination of water bodies to make it harmful for organisms is called water pollution.

We use the term water-pollution to cover the following effects:


The top layer of the earth’s crust which is loosely bound is called soil.

Formation of soil:


See Answer

1: (b) Water, 2: (a) Atmosphere, 3: (c) Carbon dioxide, 4: (d) Ozone at ground level, 5: (a) Water, 6: (a) Sun, 7: (b) Moss, 8: (d) Oxygen, 9: (c) Both a and b, 10: (a) Troposphere