Chapter Notes and Summary
• Air is present everywhere. It cannot be seen. However, it can be felt.
• Moving air is called wind.
• Air occupies empty space.
• Composition of air : Nitrogen and oxygen together constitute 99% of air.
• An object can be burnt only in presence of oxygen.
• About four-fifth of air is nitrogen. It does not support burning.
• Plants prepare their food in presence of carbon dioxide during process of photosynthesis.
• During photosynthesis, oxygen is released. Hence, it goes replenished in atmosphere.
• Animals take oxygen and produce carbon dioxide during process of respiration.
• Aquatic animals use air dissolved in water for respiration.
• Dust and smoke are also present in air.
• Smoke is released from vehicles and from burning.
• Traffic policemen wear a mask in order to filter out smoke, that is harmful.
• Dust and smoke can be seen as a streak of light when sunlight enters a dark room through a slit.
• Air also contains water vapour.
• Windmill generates electricity, when wind turns its fan rapidly. Windmills are also used to draw water from wells and to run flour mills.
• Air helps in flight of birds and insects and in movement of sailing yachts, gliders, aeroplane and paper aeroplane, etc.
• Garbage : garbage collected in garbage trucks are disposed in low lying open areas known as landfills.
This does not allow any segregation of useful and non-useful components.
• To deal with garbage, useful and non-useful components are separated.
• useful components (that rot completely) include fruit or vegetable peels, paper bags, dried leaves, etc. They must be dumped in green bins.
• non-useful components (that do not rot) include aluminium wrappers, glass pieces, old shoes, plastic bags,
etc. They must be dumped in blue bins.
• Composting : rotting and conversion of plant and animal waste into manure is known as composting.
• Materials such as plastic cannot be converted to less harmful substance by composting.
• method of preparing compost with help of red worms is known as vermicomposting.
• Recycle of materials : Some materials such as newspaper, notebooks, envelopes, etc. can be easily recycled to form useful products. Some other materials such as plastic can cause health hazards and environment problem.
Therefore, use of plastics should be minimized.
• Dealing with garbage :
(a) Minimise use of plastic bags.
(b) Use jute or paper bags.
(c) Never burn plastic bags and dried leaves.
(d) Use vermicomposting to deal with domestic waste.
(e) Do not waste paper.
Chapter Notes and Summary