photosynthesis 

1. Set up a boiling tube containing 45 cm3 of sodium hydrogen carbonate solution (1%). Allow the tube to stand for a few minutes and shake to %%disperse any air bubbles%% that might form.
2. Cut a piece of the pondweed. about 8 cm long.
3. Use forceps to place the pondweed in the boiling tube carefully. Make sure that you don't damage the pondweed.
4. Position the boiling tube so %%that the pondweed is 10 cm away from the light source.%% Allow the boiling tube to stand for five minutes. %%Count the number of bubbles emerging from the cut end of the stems in one minute.%% %%Repeat%% the count five times and record your results.
5. Calculate the average number of bubbles produced per minute. Repeat the experiment at different distances away from the light source.

Variables

• Independent variable – distance from the light source/light intensity.
• Dependent variable – the number of bubbles produced per minute.
• Control variables – concentration of sodium hydrogen carbonate solution, temperature, using the same piece of Cabomba pondweed each time.

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