A student tests lamp distances in the order 10, 20, 30 and 40 cm, using the same pondweed and solution. The solution becomes progressively depleted of carbon dioxide.
Which change would best reduce this source of bias?
Randomise distance order and increase water temperature after each gas collection period.
Randomise distance order and replace solution at a fixed carbon dioxide concentration.
Keep distance order unchanged and increase pondweed length after each gas collection period.
Keep distance order unchanged and replace solution at progressively lower carbon dioxide concentrations.
44 exam-style questions on Edexcel GCSE Biology 6.1 Photosynthesis, covering 6.1.1 Photosynthetic organisms as producers, 6.1.2a Limiting factors on the rate of photosynthesis, 6.1.2b Interactions of limiting factors on photosynthesis, and 6.1.3 Inverse square law and light intensity. Each one has a worked solution and a mark scheme showing where the marks go.