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Solved Examples on Breathing and Exchange of Gases

Question1: Intercostal muscles occur in [CBSE PMT’2008]

(a) abdomen

(b) thigh

(c) ribs

(d) diaphragm

Answer: a


At high altitude, the body undergoes numerous changes in order to increase oxygen delivery to cells and improve the efficiency of oxygen usage. The early changes include increased breathing rate and increased red blood cell production.

Question2: Which of the following statements is not true? [Kerela PMT’2008]

(a) The partial pressure of oxygen in deoxygenated blood is 40 mm Hg

(b) The partial pressure of oxygen in oxygenated blood is 95mm Hg

(c) The partial pressure of oxygen in the alveolar air is 104 mm Hg

(d) The partial pressure of carbon dioxide in deoxygenated blood is 95 mm Hg

Answer: a


During inspiration (breathing in) the pressure of air falls in the thorax because of increase in its volume which is brought about by contraction of diaphragm and Inspiratory muscles. Since lungs are situated in the thorax, therefore a fall of pressure in thorax also lowers the pressure inside lungs, due to which air from outside rushes into the lungs through nostrils, trachea and bronchi.

Question3: In ancient times, a man dies immediately although there was no injury to brain, kidney, stomach and heart. The probable cause of death may be [CPMT’2008]

(a) Coagulation of RBC

(b) Digestion stopped

(c) Diaphragm got punctured

(d) Larynx got punctured

Answer: b


If a person first inspires with his maximum effort and then expires also with maximum effort, the volume of air breathed out is called the vital capacity. An athlete requires more oxygen during exercise on a regular basis. This gradual effort of an athlete to meet his oxygen demand ultimately increases the vital capacity.

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