THORAX ABDOMEN AND PELVIS

Detailed explanation-1: -The acinus is the structure in the lung where gas exchange occurs. The sac-like structure of the alveoli increases their surface area.

Detailed explanation-2: -Broad surface area-there are several alveoli in the lungs with a form that raises the surface area more. A wide diffusion gradient means that the concentration of oxygen in the alveoli is greater than in the capillaries, meaning that oxygen is transported from the alveoli to the blood.

Detailed explanation-3: -(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.