Floating Leaf Disk- Brad Williamson
This lab tangibly demonstrates the abstract concept of photosynthesis to students. Normally, disks punched out of leaves (with a hole punch) would float. When the air spaces are infiltrated with a sodium bicarbonate solution, the overall density of the leaf disks increase and they sink. Bicarbonate ion serves as the carbon source for photosynthesis. As photosynthesis proceeds, oxygen is released into the interior of the leaf, which changes the buoyancy- causing the disks to rise. Since cellular respiration is taking place at the same time and consuming oxygen, the rate that the disks rise is an indirect measurement of the net rate of photosynthesis.