Oxygen is a gas which readily dissolves in water. The lungs contain many tiny passages called bronchioles which all end in tiny grape-like sacs called alveoli . The inside of the alveoli is moist and oxygen readily dissolves into solution. The alveoli have a good blood supply. The blood entering the lungs contains little or no oxygen.
Oxygen diffuses across to equalise the concentrations into the blood.
The presence of alveoli increases the surface area of the lungs available for gas exchange to something resembling the size of a football pitch. Diffusion is the passive movement of liquid or gas particles from an area of high concentration to an area of low concentration. Drag these parts of the breathing system to the correct description. This question works in the same way as Question 1. Question 3 Put this sequence of events into the correct order so that inhalation occurs.