Samuel investigated how light intensity affects photosynthesis and respiration in algae beads.
He placed 5 cm3 of orange hydrogencarbonate indicator solution into each of three test tubes, labelled X, Y, and Z.
All three test tubes were left in a water bath for two hours.
Hydrogencarbonate indicator solution is orange in normal levels of carbon dioxide. It turns red as the carbon dioxide levels decrease, and yellow as the carbon dioxide levels increase.
The results at the end of the experiment are shown below:
| Test tube | Colour of indicator at start | Colour of indicator at end |
|---|---|---|
| X | orange | yellow |
| Y | orange | orange |
| Z | orange | red |
Explain the colour change observed in test tube Z.
Explain the purpose of test tube Y.
Samuel set up a fourth test tube, tube W, containing algae beads in the indicator solution, and placed it in very dim light. After two hours, the colour of the indicator solution in this test tube remained orange. Explain why.
Samuel carried out another experiment to investigate the effect of light intensity on the rate of photosynthesis in a water plant.
Suggest how he could vary his independent variable.
Suggest how he could measure his dependent variable.
Suggest how he could ensure that his results were reliable.
