A student is investigating the effect of light intensity on the rate of photosynthesis in aquatic plants. The student plans to vary the distance of a light source from the plant while keeping temperature and carbon dioxide levels constant. They consider how to improve accuracy and control variables during the experiment.
Explain why controlling temperature is important in this experiment.
Show answer, mark scheme and Mentor explanation
MP1: Temperature affects the rate of photosynthesis
MP2: If temperature varies, it could change the rate independently of light intensity
Can you spot the two separate ideas the mark scheme wants here?
To secure both marks, your explanation needs to show two linked points. First, temperature affects the rate of photosynthesis. Second, if temperature changes during the experiment, the rate could change because of temperature rather than because of light intensity. This means temperature must be controlled so the effect of light intensity can be judged fairly.