Sunday 4 November 2012

CBSE class 6 - Science - CH 15 - Air Around Us

Air Around Us
Class 6 Science Air Around Us
Air Balloon
NCERT Solution and Q & A

Q1: What is the composition of air?
Answer: Air is a mixture gases, water vapours and dust particles. Largely it consists of:
  1. Nitrogen (79%)
  2. Oxygen (20%)
  3. Carbon Di-Oxide (1%)
  4. Other gases like Helium, Hydrogen etc.
  5. Water Vapours
  6. Dust particles

Q2: What are the important properties of air?

Answer: Important properties of air are:
  1. Air occupies space.
  2. Air is present every where including water and soil.
  3. Air is transparent.
  4. Air is colourless.
  5. Air is essential for life on earth.

Q3: Which gas in the atmosphere is essential for respiration?
Answer:  Oxygen is essential for living organisms.

Q4: How will you prove that air supports burning?

Answer: Place a burning candle in a tray. Cover it with a glass jar. To make it air-tight, fill tray with water. After sometime, burning candle dims and goes off. Water level also rises up in the jar. It shows air support burning.

air supports burning

Explanation: During burning, oxygen is consumed and carbon-dioxide is released. After sometime no oxygen is left inside the jar and flame goes out. Once the candle goes off, the temperature surrounding the candle cools down and volume of air (carbon dioxide) decreases. Thus water rises up little in the jar.

air is dissolved in waterQ5: How will you show that air is dissolved in water?

Answer: Take some water in a glass vessel or beaker. Heat it slowly on a tripod stand. Well before the water begins to boil, look carefully at the inner surface of the vessel. These bubbles come from the air
dissolved in water.

Q6: Why does a lump of cotton wool shrink in water?

Answer: Air is present in the cotton wool. When dipped in water, air present in wool escape and it shrinks.

Q7: Fill in the blanks:

1.  The layer of air around the earth is known as _atmosphere_.

2. The component of air used by green plants to make their food, is _carbon dioxide__.

3. Air occupies _space_.

4. Aquatic animals use _dissolved_ air in water for respiration.

Q8: List five activities that are possible due to the presence of air.

  1. Animals use air for respiration.
  2. Plants use air to prepare their food. (photosynthesis)
  3. Power generation by wind mills.
  4. Burning of fuels and substances.
  5. Air helps in the scattering of seeds and pollens of plants. (pollination).
  6. Air helps in the movements of sailing yachts, gliders, parachutes and aeroplanes.

Q9: How do plants and animals help each other in the exchange of gases in the atmosphere?

Answer:  There is the interdependence of plants and animals. Both plants and animals respire i.e. they inhale oxygen and gives out carbon dioxide in the atmosphere. Plants take carbon dioxide from the atmosphere and prepare food. This is called photosynthesis. During this process, plants give out oxygen to the atmosphere. Therefore plants and animals help each other in the exchange of gases in the atmosphere.

Q10:Why do why earthworms come out of the soil, only during heavy rains?

Answer: Most of the small organisms like earth worms, rodents live inside the soil. They usually live in burrows and holes in the soil. These burrows also make spaces available for air to move in and out of the soil. However, when it rains heavily, water fills up all the spaces occupied by the air in the soil. In this situation, animals living in the soil have to come out for respiration.

Q11: What is the use of Nitrogen?

Answer: Nitrogen is used in protein synthesis. Nitrogen is an important constituent of amino-acids which manufacture proteins, Proteins are required by living organisms to grown and repair their body parts.

Q12: How Oxygen is removed from the atmosphere?

  1. Through combustion or burning of substances,
  2. Through respiration by living beings.
  3. Rusting of iron.


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