Page 80 - Viva ICSE Science 4 : E-book

TIME TO REVISE

Circle the right answer.
1. Plants use the gas (oxygen/carbon dioxide) for photosynthesis.
2. Humans and animals need the gas (oxygen/carbon dioxide) for breathing.

3. Air (expands/shrinks) on heating.

Process of Breathing

We know that breathing is the process of taking in and giving out air. All living things
need air for their survival. Without breathing, they cannot survive. Thus, they have

special organs in their body to carry out breathing.

Plants breathe through stomata that are present on the
lower surface of their leaves. Diff erent animals have diff erent
breathing organs. Most aquatic animals breathe through

gills. Insects like ants breathe through spiracles.

Humans breathe in and breathe out air through their nose.
The act of taking in air into the lungs is called inhalation,

while the act of giving out air is called exhalation.

Air Pollution

Air pollution is the pollution of air caused when smoke and harmful gases from vehicles,
factories and other sources enter the air. Any substance that pollutes the air is called a
pollutant. Smoke, dust and harmful gases are the examples of pollutants that make our

environment dirty. They decrease the quality of air and make it unhealthy for breathing.
Besides these, germs like bacteria and viruses are also pollutants. Their presence in the

air also reduces the quality of air.

Causes of air pollution

Air pollution is caused either naturally or due to human
activities. Some natural causes of air pollution include

volcanic eruptions, dust storms and forest fi res. But
human activities are the major causes of air pollution.
It is caused by us through the use of fuels, vehicles and

electricity. Smoke released from vehicles and factories, bursting of crackers, burning of
fuels such as wood, coal, petroleum and other natural gases, spraying of insecticides and

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