3.1.1d) The mechanism of ventilation of mammals

Question 1

Inspiration - breathing in

Answer 1

Energy-using process
The intercostal muscles contract and pull the rib cage up and out
The diaphragm contracts causing it to flatten
The chest cavity gets larger causing pressure in the lungs to fall
Air moves into the lungs from the higher outside pressure

Question 2

Expiration - breathing out

Answer 2

Passive process
The intercostal muscles relax and so the rib cage returns to normal
The diaphragm relaxes pushing it up
The chest cavity gets smaller and so pressure in the lungs increases
Air flows out of the lungs