2.3 Gaseous exchange

Question 1

Role and structure of alveoli walls

Answer 1

Oxygen enters the blood and carbon dioxide is removed from it. Alveoli have a number of adaptations that increase the efficiency of this vital process.
Vast number of these air sacs, with the capillaries surrounding them, make a large surface area- equivalent two tennis courts.
Walls of the alveoli are very thin-one flattened cell thick, as with capillaries.
Inner surfaces of the alveoli are coated with a thin layer of water that allows oxygen to dissolve before travelling through the walls of the alveoli and capillaries.

Question 2

Diffusion gradient

Answer 2

Higher concentration of oxygen in inhaled air than there is in the blood. Oxygen diffuses into the blood and combines with the haemoglobin in the erythrocytes, forming oxyhemoglobin.

Carbon dioxide in the blood diffuses in the opposite direction, higher levels of this gas in the blood than there is in the alveoli. Exhaled air has higher levels of carbon dioxide and lower levels of oxygen than inhaled air.