Lesson 3 of 8

Breathing in and out

Goal: Explain breathing using volume and pressure.

Puzzles for this lesson

Breathing moves air in and out of your lungs. Muscles change the size of your chest, and the air follows, as it does in a pair of bellows.

Breathing in: the diaphragm contracts and flattens. The intercostal muscles contract and pull the ribs up and out. The chest gets bigger.
Bigger volume, lower pressure. The air outside is now at a higher pressure, so it pushes into the lungs.
Breathing out: the muscles relax. The chest gets smaller, the pressure inside rises, and air is pushed out.
Breathing is not respiration. Breathing moves air. Respiration is a chemical reaction in every cell that releases energy.

Your turn

This lesson’s activity starts here in a moment.

I can describe what the ribs and diaphragm do.I can explain why air moves in when the chest gets bigger.I can tell breathing from respiration.

This lesson on one page. Tap it to make it bigger.

Breathing Moving air into and out of the lungs

Diaphragm A sheet of muscle underneath the lungs

Ribs Bones that make a cage around the lungs

Intercostal muscles The muscles between the ribs

Respiration A chemical reaction in cells that releases energy

For teachers: AQA 3.8.3 · Pearson Edexcel 1.3 in part · Cambridge 8Bs.03