Page 28 - 新思维科学学生用书9 样章

1.3 The carbon cycle

Continued

6 Carefully place animals on the platforms in tubes C, D, E and F and fit the bungs.

perforated metal
platform small
animals
hydrogencarbonate
indicator

water plant
A B C D E F
Tube A: Tube B: Tube C: Tube D: Tube E: Tube F:
water plant water plant maggots maggots water plant water plant
and maggots and maggots
7 Record the colour of the hydrogencarbonate indicator in each tube.
8 Now wrap black paper around tubes A, C and E, so that no light can get in.

9 Leave all the tubes in the same place for at least 30 minutes. (It is even better if
you can set your experiment up in the morning, and then check it in the
afternoon.) While you are waiting:

• write down your prediction of the results you expect to find.
• draw a results chart, ready to fill in.
10 Return to your tubes and take off the black paper. Record the colour of the
indicator in each tube.

Questions
1 Use the colours of the indicator to record how much carbon dioxide is present
in each of the six tubes.

2 All organisms respire all the time. In which tubes were organisms respiring?
3 Plants also photosynthesise when they have light. In which tubes were plants
photosynthesising?
4 In the light, plants photosynthesise faster than they respire.

a In which tubes would you expect carbon dioxide to be used?
b In which tubes would you expect carbon dioxide to be given out?
5 Use your answers to the questions above to explain your results. (If your results
do not match what you expect, try to suggest why they do not.)

6 Suggest why you were asked to put a little platform into each tube, even if there
were no animals to put onto it.

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