How are the alveoli designed to maximise the exchange of gases?
The alveoli are designed to maximise the exchange of gases by providing a very large surface area. If the alveolar surface were spread out, it would cover about 80 m², which makes the exchange of gases highly efficient.
The walls of the alveoli contain an extensive network of blood-vessels. This network allows blood to bring carbon dioxide from the body for release into the alveoli and transport oxygen from the alveolar air to the rest of the body.
Furthermore, the lungs always contain a residual volume of air during the breathing cycle. This ensures there is sufficient time for oxygen to be absorbed and for carbon dioxide to be released.
Explanation
The answer correctly identifies the three specific design features mentioned in the textbook context: the large surface area (80 m²), the extensive network of blood vessels, and the presence of residual volume. These points directly address how the structure facilitates efficient gas exchange.