Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between the air in the alveoli and blood in the capillaries around them. (5 marks)

The lungs have million of alveoli which increases the surface area, therefore increasing the rate of diffusion of oxygen into the lungs. The alveoli are very thin walled, which reduces the diffusion pathway of oxygen therefore slowing it to diffuse through quickly. The lungs are also well ventilated, which means fresh air with plenty of oxygen is continuously introduced into the alveoli - maintaining a diffusion gradient, which allows the oxygen to diffuse from the air into the alveoli quickly.