Which of the following statements(s) is (are) true about respiration?
(a) During respiration, ribs move inward, the diaphragm is raised.
(b) In the alveoli, exchange of gases takes place, i.e., oxygen from alveolar air diffuses into blood and carbon dioxide from the blood into the alveolar air.
(c) Haemoglobin has a greater affinity for oxygen than carbon dioxide.
(d) Alveoli increases the surface area for the exchange of gases.

(a) and (d)
(b) and (c)
(a) and (c)
(b), (c) and (d)


The correct option is D (b), (c) and (d)
Hint: Respiration is the biochemical process that involves the production of energy by combining oxygen and glucose, resulting in the release of carbon dioxide, water, and ATP (energy).

Part 1 - Definition - Mechanism of Breathing
  • The respiratory system enables oxygen to enter the body and carbon dioxide to leave the body through breath in and breath out, respectively. 
  • To forces, the air to move from outside into the lungs, the pressure in the lungs needs to be lower than the atmospheric pressure.
  • The contraction of the diaphragm increases the volume of the thoracic chamber in the front and back. 
  • This volume is further increased by the contraction of external intercostal muscles, which lifts up the ribs and sternum.
  • While during exhalation, the diaphragm and the intercostal muscles relax, the ribs and sternum return to their normal positions.

Part 2 - Process of Gaseous exchange within Alveoli
  • There are millions of alveoli within each lung that serves as the actual site of gaseous exchange. 
  • There is an extensive network of blood capillaries and blood vessels here.
  • As the air enters our lungs through the nasal passage, the alveoli get filled with air.
  • The oxygen is taken in by the blood vessels in the alveoli. Blood contains a pigment called haemoglobin that has a great affinity for oxygen.

Part 3 - Conclusion
  • Statement (a) is incorrect as during inhalation ribs move outward and the diaphragm contracts (lowered) to increase the volume of the thoracic cavity.
  • Statement (b) is correct as alveoli are the actual site of gaseous exchange.
  • Statement (c) is correct because haemoglobin does have a greater affinity for oxygen as compared to carbon dioxide.
  • Statement (d) is also correct as the presence of these many alveoli actually increases the surface area of the lungs by many folds.

Final step:  Statements (b), (c), and (d) are true regarding respiration. Hence option D is correct answer.


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