Question

How are oxygen and carbon dioxide transported in human beings? How are lungs designed to maximise the area for exchange of gases?

Answer 1

 (i) Oxygen enters the human body through the nasal passage and reaches the lungs.
(ii) Numerous alveoli are present in the lungs. These alveoli are surrounded by many blood capillaries. From the alveoli, O2 is taken up by the red blood cells present in the blood capillaries.
(iii) Similarly, the CO2 from the various tissues is transported to the alveoli. (iv) This CO2 is then released through the nasal passage during exhalation. Alveoli are the sites of exchange of gases. Each lung contains 300−350 million alveoli. These alveoli increase the surface area for gaseous exchange, making the process of respiration more efficient.

Answer 2

Answer:

• The exchange of gases in the human body is called breathing which is required for respiration. Inhalation is the intake of air for the transport of oxygen to the cells of the body and exhalation is the release of air from the body for the transport of carbon dioxide from cells to outside.
• Transport of oxygen - 97% of the oxygen transport to cells and remaining 3% dissolves in the plasma during respiration. Haemoglobin pigment in RBCs transports oxygen to the cells. Oxygen molecules get attached to the iron of haemoglobin pigment and it becomes oxyhaemoglobin. This oxygenated blood is then distributed to body cells by the heart. It gives oxygen to cells and collects carbon dioxide, and becomes deoxygenated blood.
• Transport of carbon dioxide - Haemoglobin has less affinity for carbon dioxide. Hence, only 20-25% carbon dioxide transfers through blood in the form of carbamino-haemoglobin, 7% dissolve in plasma, and rest transports as bicarbonate. When blood reaches to alveoli, carbon dioxide dissociates from haemoglobin due to high partial pressure of oxygen in the presence of carbonic anhydrase enzyme. Bicarbonate also releases carbon dioxide when it reaches the alveoli. And carbon dioxide releases from the body via exhalation.
• Lungs are designed very well to maximize the area for exchange of gases. It is lined by a thin membrane. It is divided into small units, bronchi further to bronchioles. Balloon-like structures, called alveoli, are present at the end of these bronchioles that increase the surface area of lungs for the exchange of gases.

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