Class 6 Science Chapter 11 Practice Question Answers - Air Around Us

Q1: Solve the following multiple-choice questions given below: Wind does not help in the movement of which of the following?
(a) Weathercock
(b) Sailing yacht
(c) Ceiling fan
(d) Firki
Ans: (c)
A ceiling fan runs on electricity; hence, wind doesn’t help in the movement of the fan.

Q2: Explain why burning a fire in an enclosed room causes people to suffocate.
Ans: Any burning substance requires oxygen to burn and releases carbon dioxide. In a closed room, there is limited oxygen supply, and the carbon dioxide released cannot be accumulated nor expelled.As a result, in a closed room with fire, humans have less oxygen to breathe and later start inhaling the carbon dioxide released. Carbon dioxide is harmful to humans as it combines with haemoglobin present in the blood faster than oxygen. Resulting in asphyxia which proves to be fatal.

Q3: Why should we breathe through our nose and not our mouth?
Ans: The human nose has two nostrils, each coated with a dense layer of tiny nostrils and a thick layer of mucus. The tiny hairs act as filters, removing smoke particles and dust, allowing air free of dangerous airborne particles to enter our respiratory system. As our mouth lacks all these filters, it is not advised to breathe through the mouth.

Q4: Explain the reasons for the following statements:

1. A firki does not rotate in a closed area.
   
2. The arrow of the weathercock points towards a particular direction at a particular moment.
   
3. An empty glass, in fact, is not empty.
   
4. Breathing through the mouth may harm you.
   

Ans:

1. There is a lack of air movement in a closed area, which prevents firki rotation. Because of the moving air all around, a firki usually rotates when placed in an open area.
2. A weathercock is a device that indicates the direction of the wind. It is made up of an arrow that is mounted at its centre of gravity and can freely rotate around a vertical axis. As a result, the arrow points in a specific direction at a specific time to indicate the most recent direction of the wind’s movement.
3. An empty glass is not empty; it contains air. It can be demonstrated by using a simple experiment. Place an empty bottle upside down in a beaker that is filled with water. Water does not enter the bottle when pushed inverted because there is no space for the air to escape.When the bottle is tilted, the air escapes as bubbles, and the empty space is filled with water. This demonstrates that even an empty glass contains air.
4. Yes, breathing through our mouths can be harmful. The air may contain gases, water vapour, and dust particles. When we breathe in through our nostrils, the fine hair and mucus in our nose keep dust particles from entering our respiratory tract. However, if we breathe through our mouths, harmful dust particles may enter our bodies and make us sick. As a result, breathing through the mouth may be harmful.

Q5: The blanket of air surrounding the earth is known as ________.
Ans: The blanket of air surrounding the earth is known as the atmosphere.

Q6: The component of air used to make food by green plants is ___________.
Ans: The component of air used to make food by green plants is carbon dioxide.

Q7: How do plants and animals help each other in the exchange of gases in the atmosphere?
Ans: Two processes, respiration and photosynthesis, help plants and animals exchange the gases in the atmosphere. In respiration, plants and animals take in oxygen and give out carbon oxide.
Plants, during the day, take in carbon dioxide and synthesise food, giving out oxygen into the atmosphere as a byproduct. Thus, plants and animals help each other in the exchange of gases and maintain the balance of gases in the atmosphere.

Q8: What is the composition of air?
Ans: Atmospheric air comprises oxygen(21%), nitrogen(78%), carbon dioxide, water vapour and pollutants(1%) like dust and smoke.

Q9: Why does a lump of cotton wool shrink in water?
Ans: A lump of cotton wool shrinks in water as air pockets are present in the cotton. When it is dipped in water, air pockets are replaced with water, making the cotton fabric stick together. This causes the cotton wool lump to shrink in water.

Q10: Which are the five processes that require the presence of air?
Ans: Processes which require the presence of air are:

• Cloud formation
• Respiration
• Transpiration
• Winnowing
• Photosynthesis