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How are lungs designed in human beings to maximize the area of exchange of gases?
A) Presence of a huge number of alveoli.
B) Presence of a huge number of alveoli which possess a network of capillaries over their surface.
C) Presence of a huge number of alveoli which possess a network of capillaries over their surface, functioning a respiratory surface.
D) None of these.

Answer Verified Verified
Hint: Lungs play a major role in the respiratory system. A pair of lungs are designed in humans in such a way that they are lined by a thin membrane where the smaller tubes called bronchioles a balloon-like structure and the surface area for the exchange of gases have been increased by the alveoli and network of blood capillaries.

Complete Answer:
- The exchange of gases can take place on the surface which is provided by the alveoli. The walls of the alveoli are supplied with an extensive network of blood vessels.
- So lungs maximize the area for a gaseous exchange through the presence of large numbers of alveoli which are richly supplied with blood.
- To make a gas exchange in lungs the alveoli are adapted to happen easily and efficiently.
- The lungs are really given a big surface area by them. Just one cell thick and they have thin walls that are moist. There are a lot of tiny blood vessels which are called capillaries.
- In the lungs, the presence of alveoli with shape can further increase the surface area and cause a large surface area.
- A short diffusion distance of alveolar walls is one cell thick providing gases a thin wall.
- Gases dissolve in the moisture helping them to pass across the gas exchange surface of moist walls.

Hence, option B: The presence of a huge number of alveoli which possess a network of capillaries over their surface is the correct answer.

Note: The primary function of the lungs involves the transfer of oxygen from inhaled air into the blood and the transfer of carbon dioxide from the blood into the exhaled air. To increase the density of gas exchange surface alveoli are formed on the acinar airway tree, thus facilitating the diffusion of oxygen to and into the capillaries.
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