4th Standard Science Term-III
Air We Breathe
Introduction
Our earth consists of land, water and air. All these components are very much important for the survival of all living creatures. Air is present all around us. It is very important to cause rain and for the growth of crops. It is needed for the respiration of plants and animals.
Importance of Air in Our Daily Life
1. Oxygen present in air is needed for respiration.
2. We can hear the sound only when there is air around.
3. Air helps in the dispersal of seeds for plant reproduction.
4. Monsoon and rain occurs due to the wind action.
5. Air regulates the atmospheric temperature.
Air is a Mixture
The air we breathe consists of a mixture of gases. It contains dust, water vapour and smoke. Air also contains gases like oxygen and nitrogen. Air shows the properties of all the gases present in it.
For example, air supports combustion because oxygen is present in it. While cooking using firewood, fanning air helps in burning of firewood.
Composition and components of air
The composition of air is not constant. It varies from place to place and over time. Air is not a single element; it is made up of different substances.
Nitrogen
The amount of nitrogen present in air is about 78%.
It is used to fill up food package to extend their shelf life.
Liquid nitrogen is used to store living cells.
Plants need nitrogen for their growth. We can see root nodules containing nitrogen in some plants.
Nowadays people use nitrogen gas to fill the tyres of their vehicles. Some compounds of nitrogen are used as explosives also.
Oxygen
It is one of the main components of air. The amount of oxygen present in air is about 21%. All the creatures cannot live without oxygen. The presence of oxygen can be tested with simple experiments.
Uses of oxygen
1. All living things use oxygen for breathing.
2. Oxygen is essential for burning.
3. Oxygen cylinders are used in hospitals to enable the patients to breathe when they cannot breathe normally.
4. Oxygen is used in gas welding.
Carbon dioxide
The amount of carbon dioxide present in air is only 0.03%. Though it is less in percentage its uses are more and essential. It can be tested with lime water. The lime water changes from colourless to milky.
Uses of carbon dioxide :
1. Carbon dioxide helps plants in photosynthesis.
2. It is used in fire extinguishers.
3. It is used in refrigerators as dry ice for cooling purposes.
4. It is used to make plastics and polymers.
Air has other gases like hydrogen, helium, argon etc. in small proportion. Air also contains water vapour which varies according to the environment. When we breathe, we take oxygen from air and release carbon dioxide and water vapour to air.
Air pollution
The atmosphere of earth is disturbed by human activities. This leads to environmental problems like air contamination and global warming. The air carries soot, smoke and other particles from car exhaust and power plants. These are the major contributors to air pollution.
Adverse effects of Air pollution
Global warming
This changes the climatic conditions of different regions of the world. It also causes disturbances in agriculture and food production. Melting of snow caps and increase in sea levels are the consequences of global warming.
Formation of smog
When dust particles and smoke combine with fog in the presence of sunlight, smog is formed. It reduces the visibility. It also causes many respiratory disorders and allergies.
Formation of acid rain
Sulphur dioxide and
nitrogen oxides react with water in the atmosphere producing sulphuric acid and nitric acid. These acids come down along with the rain. This is called acid rain.
Acid rain
- causes respiratory and skin disorders
- damages the leaves and affects the productivity of plants.
- enters the ground and river waters causing harm to the aquatic life.
- erodes marble and damages monuments like Taj Mahal.
Aerosol formation
When liquid or solid particles are dispersed in air, it is called aerosol. Aerosols are deposited on the leaves affecting photosynthesis.
Depletion of Ozone
The hydrocarbons such as the Chlorofluorocarbons (CFCs) destroy the ozone layer. Ozone holes allow the UV rays to reach the earth's surface. UV radiation harms wildlife, damages plants and causes skin cancer in humans.
Effects of Air pollution of human beings
Air pollution has bad impact on human health. When the pollutants increase in air, they cause irritation in the eyes, nose and throat. Air pollution can also produce wheezing, coughing and breathing problems in humans.
Some of the major effects of air pollution on human beings are :
1. Respiratory diseases. E.g. Tuberculosis
2. Cardiovascular damage.
3. Fatigue, headaches and anxiety.
4. Nervous system damage.
Steps to check air pollution
Air pollution can be reduced by the following steps.
1. Alternative source of energy (E.g. Solar energy) should be used.
2. Air filters should be used to prevent harmful gases mixing with air.
3. Smoke emission test and certification of motor vehicles must be enforced.
4. More trees should be planted to absorb carbon dioxide.
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