1. Breathing Inhaling – breathing IN

2. Breathing IN CO 2 levels rise –detected by Medulla oblongata (brain) Impulse sent to diaphragm and intercostal muscles from brain Diaphragm contracts and goes down (flat) Intercostal muscles contract and ribs move out and up

3. Volume of chest increases Pressure INSIDE the chest drops (more space) Internal pressure now less than outside pressure Air goes INTO the lungs to equalise the pressure. Oxygen enters blood by diffusion, Carbon dioxide leaves the blood by diffusion and is exhaled.

4. Breathing OUT Diaphragm RELAXES and goes UP (domed) Intercostal muscles RELAX & ribs move DOWN and IN Volume of chest decreases Pressure in the chest increases Internal pressure now HIGHER than outside pressure Air LEAVES the lungs to equalise the pressure. CO 2 leaves the body

5. Composition of Air 21 16 40.04 79 variessaturated Exhaled air is also warmer than inhaled air.

6. Do I know it? Breathing IN Which gas triggers when its levels rise –this detected by ??? Impulse sent to diaphragm and intercostal muscles from brain Which two muscles now contract? CO 2 Medulla oblongata (brain) Intercostal muscles and Diaphragam

7. Do I know it? Breathing IN When the chest volume gets bigger what happens to the internal pressure? What causes air to enter the lungs? What is percentage of oxygen in exhaled air? It drops or decreases The external pressure is now higher (or vice versa) 16%