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Unit 19: Biology Part 2 Page 99 of 137

Activities and Experiments

Lesson 4: Respiratory & Excretory Systems

Experiment: Oxygen All Around

We breathe in the air that is around us. In order for respiration to work,
there must be oxygen in this air. But can we prove that there actually is
oxygen in the air around us? This experiment will do exactly that.

Materials:

 Small amount of water
 Pan
 Candle

1. Place a small amount of water in the bottom of a pan. The bottom
of the pan should be covered.
2. Light a candle and carefully place it in the water on the bottom of
the pan.

3. Cover the lit candle with the glass and observe what happens.

What’s happening: Fire needs fuel, heat, and oxygen. The candle was

getting oxygen from the air around it – the same air we breathe. When the
candle had no more oxygen, the flame went out.

Experiment: How Long Can You Hold Your Breath?

Although you normally breathe without thinking about it, you can, of course,
hold your breath. Your brain will not allow you to hold your breath longer

than is safe.

Materials:

 Plastic bag
 Pen
 Paper

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