Air – Maharashtra Board Class 8 Solutions for General Science (English Medium)
Air contains oxygen, nitrogen, carbon dioxide, water vapour and some inert gases.
Proportion of constituents of air:
- Nitrogen – 78%
- Oxygen – 21%
- Other gases – 1%
Plants use carbon dioxide during photosynthesis.
The conversion of atmospheric nitrogen into compounds such as ammonia and nitrates which can be used by living things is called nitrogen fixation. This can occur by both biological and atmospheric factors.
- Bacteria found in the root nodules of leguminous plants help in nitrogen fixation.
- During lightning, atmospheric nitrogen and oxygen combine to form nitric oxide which is oxidised again to form nitrogen dioxide.
The Government and the public have taken up the task of controlling atmospheric pollution. Some of the necessary measures which need to be taken are
- A law has been enacted making it mandatory to treat chemical waste before letting it out of a factory.
- Efforts should be made to make changes in chemical processes which may avoid the generation of harmful substances.
- Precautions should be taken to prevent concentration of harmful chemical substances.
- Industries should be installed with high chimneys and should be established away from cities.
- Engines of motor vehicles should be serviced properly to avoid pollution.
- More trees should be grown to reduce air pollution.
ill-effects of pollution:
- It leads to respiratory diseases, cancer of the intestines, high blood pressure, eye disorders and disorders of the urinary bladder.
- Capacity of milk production in animals decreases.
- There is a fall of rate of photosynthesis.
- Plants are also affected like there is an increased fall of leaves and absence of fruiting.
Functions of an observatory:
- An observatory records observations of atmospheric factors such as temperature, pressure, velocity of winds and humidity.
- It forecasts the weather based on the changes observed in various atmospheric factors.
The proportion of carbon dioxide in the air has risen which may even rise more in the future. This leads to increase in the atmospheric temperature. The rising proportion of carbon dioxide increases the threat from the greenhouse effect.
Nitrogen is utilised by living organisms as it is an important constituent of proteins. It is released back in the atmosphere by excretion, burning and decay of living things. So, its proportion remains constant in air.
Carbon dioxide dissolves sparingly in water and has to be dissolved in water under pressure. So when a bottle of an aerated drink is opened, the pressure is released and the carbon dioxide gas gushes out in a stream of bubbles.
- Oxygen does not burn, but supports burning.
- Some deliquescent substances absorb water vapour from the air.
- It is mandatory to treat chemical waste before letting them out.
- Solid carbon dioxide is also called dry ice.
|a. Potassium chlorate||4. Oxygen|
|b. Micro-organisms||5. Nitrogen fixation|
|c. Greenhouse effect||3. Carbon dioxide|
|d. Fertilizers||2. Nitrogen|
|e. Manganese dioxide||1. Catalyst|
a. Water vapour
b. Carbon dioxide
e. Nitrogen dioxide