To show that carbon dioxide concentration effects the rate of photosynthesis
Materials and Equipment

Water bath at fixed temperature (25oC)

Cold, boiled water (to remove all CO2)


Test tube

Bench lamp at fixed distance


Sodium hydrogen carbonate 


1 Set up the apparatus as shown in the diagram.
2 Add 5cm3 sodium hydrogen carbonate to the water in the test tube with the pondweed.
3 Position the lamp at a fixed distance from the beaker (about 20 cm)
4 Allow the pondweed to settle for about ten minutes.
5 Record the number of bubbles of oxygen produced per minute from the pondweed. (This will give an indication of the rate of photosynthesis)
6 Repeat and get the average.
7 Add a further 5cm3 sodium hydrogen carbonate to the test tube.
8 Repeat steps 4 to 6 and continue to do so, adding an extra 5cm3 of sodium hydrogen carbonate each time. Stop when there is no further increase in the rate of release of bubbles.

Record your results as follows