why the leaf discs rise when photosynthesis takes place
9.4.2.2 Cycles & Energy Flow overall density of the lead disk increases and the leaf disk sinks. When sodium bicarbonate is added to the water, the bicarbonate ion acts as a carbon source for photosynthesis causing the leaf disks to sink. As photosynthesis proceeds, oxygen is released into the interior of the leaf, which changes its buoyancy causing the disk to rise.