How gaseous exchange takes place at blood level? (AS1)

1. The exchange takes place in the millions of alveoli in the lungs and the capillaries that envelop them.

2. Gaseous exchange occurs between alveoli and capillaries through Diffusion.

3. The exchange of oxygen and carbon dioxide takes due to the difference in their concentrations.

4. When the blood surrounding the alveoli has a lower concentration in oxygen than alveolar air, oxygen moves into the capillaries.

5. When the blood has a higher concentration of carbon dioxide than in the alveoli, it moves into the lungs from where it is exhaled.