Page 9 - 新思维科学学生用书9 样章

1 Photosynthesis and the carbon cycle

Think like a scientist

Collecting the gas produced in photosynthesis

You are going to use a plant that grows in water for this experiment. This makes it easy
to collect the gas that it releases.

You will need:
• the apparatus shown in the diagram.

If you do not have any pond water, you can use gas collecting

ordinary tap water. test tube
You can use any plant that grows under water. You
can often buy water plants in pet shops, because beaker
people like to put them into tanks with their pet fish. pond water

Method upside down
1 Set up the apparatus shown in the diagram. funnel
2 Put the apparatus in a place where the water water plant

plant will get sunlight. Leave it for at least one block to
support funnel
day.
3 When plenty of gas has collected in the top of the test tube, put your hand
into the beaker of water. Carefully remove the tube from the top of the funnel.

Keep the opening of the tube under the water, or the gas will escape!
4 With the tube still upside down, put your thumb over the end of the tube, to
keep the water and gas inside.
5 Take the tube out of the water, keeping your thumb over the end. Keep the tube

upside down.
6 Very carefully, move your thumb just a little bit, so that the water runs out of the
tube but the gas stays inside. Push a stopper into the tube, then place it – right
way up – in a test tube rack.

7 Light a splint, and then blow it out so that it is glowing but not burning.
8 Test the gas with the glowing splint. (Try not to touch the wet sides of the test
tube, or the splint will be extinguished!) If the gas contains a lot of oxygen, the
splint will relight.

Questions
1 Explain why it was best to use a water plant in this experiment.
2 Explain why it was important to leave the apparatus where it would get plenty of

sunlight.

8