Teachers, save “1.2 The respiratory system” to assign it to your class.

Think like a Scientist 1 Make a model to explain breathing You will need: A plastic bottle, a narrow plastic tube or straw, an elastic band, scissors, two balloons, electrical tape, sticky putty, or plasticine play dough. 1 Cut the bottom off the plastic bottle. Safety: Take care not to cut yourself with the scissors or sharp edge of the cut bottle. 2. Tie a knot in the narrow end of one balloon and cut off the other end 3 Stretch the newly cut end of the balloon around the bottom of your plastic bottle. Use the electrical tape to fix the balloon in place. 4 Put a plastic tube or straw in the neck of the other balloon and fix it in place with the elastic band. Be sure not to make the elastic band so tight that it crushes the straw. The air must flow through, so blow gently through the straw to see if the balloon inflates. 5 Put the straw and the balloon into the neck of the bottle. Put the play dough around the neck of the bottle to seal the bottle. Again, make sure that you don't crush the straw. 6 a Pull on the bottom balloon and observe what happens. b Let go of the balloon. What happens?