- occurs in the alveoli and takes place by diffusion
- the alveloli are surrounded by capillaries so oxygen and carbon dioxide diffuse between the air in the alveoli and the blood in the capillaries
- there is a high concentration of oxygen in the alveoli and a low concentration of oxygen in the blood so oxygen diffuses from the alveoli into the blood
- there is a high concentration of carbon dioxide in the blood and a low concentration in the alveoli, so carbon dioxide diffuses from the blood into the alveoli
- both oxygen and carbon dioxide carry haemoglobin
- haemoglobin carries oxygen to be exchanged at the working muscle and carbon dioxide to be exchnaged at the lung
As the blood passes through the capillaries in the alveoli, oxygen diffuses into it and carbon dioxide diffuses out of it.
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