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 how the student could improve the accuracy of measuring the rate of photosynthesis in this investigation.
Show answer, mark scheme and Mentor explanation
MP1: Measure oxygen produced more precisely, e.g. collect the gas and measure volume (cm³) using a gas syringe/measuring cylinder rather than just counting bubbles
MP2: Repeat readings at each distance and calculate a mean to reduce the effect of random error
Can you spot the two exact improvements the mark scheme wants?
This question is testing whether you can identify how to make the measurement of photosynthesis more accurate. One marking point is about measuring the oxygen more precisely, for example by collecting the gas and measuring its volume in cm³ with a gas syringe or measuring cylinder instead of only counting bubbles. The other marking point is about reliability of results: repeat the readings at each distance and calculate a mean so random error has less effect.