Why do we test each distance 3 times, and work out an average?

What is the rate of photosynthesis directly proportional to?

Which of these will increase the rate of photosynthesis?

Which of the following could best explain why a student studying bubbles of oxygen given off from pondweed obtained a result of 81 in one experiment, and 9 bubbles in a second experiment?

In an investigation on photosynthesis, why did a student add sodium hydrogencarbonate to the water?