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How Plants Feed : Question 1
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The following experiment was set up to investigate how a pondweed breathes in the light and in the dark.

 

pondweed

 

Note: The carbon dioxide indicator is a coloured liquid which does not harm the plant. It can have three colours:

 

Purple or violet = No carbon dioxide
Red = A little carbon dioxide
Yellow = A lot of carbon dioxide

 

At the beginning of the experiment the carbon dioxide indicator was red. All three tubes were left in the light for a few hours. Then the colour of the indicator liquid was recorded.

 

1. Why was the aluminium foil wrapped around tube B?

 

2. Why were the tubes filled to the top with liquid and stoppered with rubber bungs?

 

3. Tube C had no plant in it, just indicator liquid. Why was it important to include this tube in the experiment?

 

4. Colour the tubes in the diagram opposite in the colours you think they should have after a few hours.

 

Pond Weed

5. What does this experiment tell you about the way green plants, such as the pondweed, exchange gases in the light and in the dark?