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Unit 19: Biology Part 2 Page 100 of 137

1. Hold your breath, with your nose plugged, and count how long you can
do it
2. Record your time.
3. Breathe into a plastic bag for one minute.
4. Hold your breath again and count how long you can do it now.

What’s happening: You should have found that you could hold your breath
less time after breathing into the bag. As you breathed into the bag, there
was more carbon dioxide in the bag, meaning there was less oxygen going
into your body with each breath. With less oxygen, you can hold your
breath for less time.

Experiment: A Diaphragm’s Duty

When you breathe in, the diaphragm muscle contacts, making more space in
the chest, which allows air to come in. When you breathe out, the opposite
happens. In this activity, you will create a model diaphragm to demonstrate

this important job.

Materials:

 2 pieces of straw (2 inches)
 Scissors
 Small balloon

 Large balloon
 Rubber bands
 Rubber cement or glue

1. Take a piece of straw about 5 cm (2 inches) long and cut a small triangle
in the center. The cut-out should only be on one side of the triangle.

2. Place a small balloon over each end of the straw and secure it with a
small rubber band.

3. Blow into the triangle cut-out to make sure that air will go into each
balloon.
4. Bend the straw in the middle of the hole.
5. Take a second piece of straw and cut a V-shape on the end. Fit the

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