CBSE Class 10 Answered

The nasal cavity conditions the air to to be received by the areas of the respiratory tract and nose. Owing to the large surface area provided by the conchae, the air passing through the nasal cavity is warmed or cooled to within 1 degree of body temperature. Cilia and mucus along the inside wall of the nasal cavity trap and remove dust and pathogens from the air as it flows through the nasal cavity.

Breathing is largely driven by the muscular diaphragm at the bottom of the thorax. Contraction of the diaphragm pulls the bottom of the cavity in which the lung is enclosed downward, increasing volume and thus decreasing pressure, causing air to flow into the airways. During normal breathing, expiration is passive and no muscles are contracted (the diaphragm relaxes).

The alveoli greatly increase the surface area of respiration. There are some 300 million alveoli in two adult lungs. These provide a surface area of some 160 m² .

The alveoli provide a surface where actual exchange of gases take place during respiration. The blood brings carbon dioxide from the rest of the body for release into the alveoli and the oxygen in the alveolar air is taken up by blood in the alveolar blood vessels to be transported to all cells in the body.