In order to monitor the rate of photosynthesis, we can conduct an experiment using the leaf disk method.
Due to air/gas found in the the inter-cellular spaces between the leaf, the disk will float on water. When the air is evacuated from the flasks (containing the leaf and the water), the leaf will lose its CO2 causing it to sink to the bottom. Therefore, a source of CO2 has to be added to the disks so that photosynthesis can happen again. This will be supplied by a sodium bicarbonate buffer system. When placed in water, an equilibrium will occur and some of the bicarbonate will become carbon dioxide. With this, the leaf will rise up back to the surface.
Hope this helps.
