(a) Explain how, the air we breathe in gets cleaned while passing through the nasal passage. (b) Why do the walls of trachea not collapse when there is less air in it? (c) How are oxygen and carbon dioxide exchanged in our body during respiration? (d) How are lungs designed in human beings to maximize the exchange of gases?

• The nasal passage plays a vital role in the purification of Nasal passage contains mucus and hair in it. The hair prevents the dust particles entering the respiratory tract and mucus also plays in preventing the fine particles of dust from entering into the track.
• The walls of the trachea do not collapse when there is less air in it because the trachea is supported by rings of soft bones called cartilage.
• The alveoli of lungs play a major role in the exchange of The oxygenated air diffuses from the alveoli into the blood. When the blood is circulated in different parts of the body, the oxygen is

carried to all cells and tissues through this blood. This oxygen is combined with the digested food and releases energy in the cell. Carbon dioxide which is produced as a waste product during respiration is diffused into the blood. Blood brings back the carbon dioxide into alveoli and then it is exhaled through nostrils passing through trachea.

• The human lungs have been designed to maximize the exchange of

There are millions of alveoli in the lungs. The presence of millions of alveoli in the lungs provide a very large area for the exchange of gases. The availability of large surface area maximizes the exchange of gases.