GCSE Biology: Gas Exchange in the alveolus

Gas Exchange in the alveolus

Source

Gas Inhaled (%) Exhaled (%)
Oxygen
Carbon Dioxide
Nitrogen
Water Vapour
21
0.04
78
Varies
16
4
78
Saturated

When we breath in, the intercostal muscles contract to move the ribs upwards and outwards. The diaphragm contracts and moves downwards. The volume inside the chest increases. This causes air to rush into your lungs and your lungs to inflate.

When we breath out, the intercostal muscles relax to move the ribs downwards and inwards. The diaphragm relaxes and moved downwards. The volume inside the chest decreases. This causes air to rush out of the lungs and they deflate.