Energy > control

It is fairly easy to show that plants produce oxygen and starch in photosynthesis. At age 14–16 students may have collected the gas given off by pond weed (for example Elodea) and tested leaves for starch.

This procedure offers a method for measuring the rate of photosynthesis which depends directly on the rate of uptake of carbon dioxide by the photosynthetic organism. Hydrogencarbonate indicator changes colour with pH, which is determined by the concentration of carbon dioxide in solution.