- Books Name
- Science Made Easy Science Book
- Science Made Easy
- CBSE Class 9
→ Air is a mixture of different gases.
→ Air contains oxygen which is essential to living organisms for respiration. So it is called breath o
→ An increase in the content of harmful substance (pollutants) in the air like carbon dioxide, carb
monoxide, oxides of sulphur, nitrogen, fluoride, lead, nickel, arsenic and dust particles etc. causes a
Air pollution can cause:
• In humans: Respiratory and renal problems, high blood pressure, eye irritation, cancer.
• In plants: Reduced growth, degeneration of chlorophyll, mottling (patches/spots of colour) of
Water: A wonder Liquid
→ The most unusual natural compound found on earth and which fulfills almost various demands
different living things.
→ About three-fourth of the earth surface is 75% are covered with water.
→ It is present underground, a very large area on the surface (sea, ocean etc.) and also in the form
of water vapour in the atmosphere.
Necessity of Water for all Organisms
→ It maintains a uniform temperature of the body.
→ All cellular processes take place in a water medium.
→ All the reactions that take place within our body and within our cells occur between substances
that are dissolved in water.
→ Water forms the habitat of many plants and animals.
→ When water becomes unfit for drinking and other uses, then water is said to be polluted.
Causes of Water Pollution
→ Dumping of wastes from the industries into water bodies.
→ Washing of clothes near water bodies.
→ Spraying chemical in water field.
→ Dumping household wastes into the water bodies.
→ Soil is the portion of the earth surface consisting of disintegrated rock and decaying organic
material. It provides the support for many plants and animals.
Creation of Soil: Various Factors
→ The sun heats up rocks during the day so that they expand. At night these rocks cool down and
→ Since all parts of the rocks do not expand and contract at the same rate, this results in the
formation of cracks and ultimately the huge rocks breaks up into smaller pieces.
→ Fast flowing water carries big and small particles of rock downstream. These rocks rub against
other rocks and the resultant abrasion causes the rocks to wear down into smaller particles.
→ Wind carries sand from one place to another.
→ Lichen (A slow growing plant)
→ Lichen, moss also grow on surface of rocks. While growing, they release certain substances tha
cause the rock surface to powder down and form a thin layer of soil.
→ Carrying away of upper fertile layer of soil by rain, wind, human activities and wrong agricultura
practice is called soil erosion.
Causes of soil erosion
→ Over grazing of land.
→ Removal of top soil by wind and water.
→ Due to lack of trees the upper layer of soil is eroded by air and water.
→ Leaving land uncultivated for long time.