Page 27 - 新思维科学学生用书9 样章

1 Photosynthesis and the carbon cycle

Think like a scientist

How do plants and animals affect carbon dioxide concentration?

In this investigation, you are going to think about two processes that you have learnt
about – respiration and photosynthesis – and how they affect the concentration of
carbon dioxide.

You will need:
• six clean test tubes, and a beaker or rack to stand them in, rubber bungs to
fit the test tubes, small pieces of perforated metal (e.g. zinc gauze) to make

platforms inside the tubes (see the diagram), some small pieces of water
plant, some small animals such as maggots (fly larvae) or woodlice, blunt
forceps (tweezers) for handling the plants and small animals, some black
paper and sticky tape, some hydrogencarbonate indicator solution.

Note
The animals did not volunteer to be part of your experiment. Treat them with care.

After the experiment is finished, put the animals back into their container, or a safe
place outside.
Hydrogencarbonate indicator solution is a liquid that changes colour depending
on the concentration of carbon dioxide. The colours are:

• purple when there is no carbon dioxide
• red when there is a low concentration of carbon dioxide
• yellow when there is a high concentration of carbon dioxide.

Method
1 Label the tubes A, B, C, D, E and F.

2 Use the pieces of perforated metal to make small platforms that can fit inside
the tubes. The platforms will stop the animals from falling into the liquid.
3 Take the platforms out of the tubes. Pour about 3 cm depth of
hydrogencarbonate indicator into each tube.

4 Put a piece of water plant into the indicator in tubes A, B, E and F.
5 Put the platforms back into the tubes. Try to make them level, with each one at
approximately the same position in each tube.

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