This lab activity demonstrates the process of photosynthesis through the production of oxygen in a plant leaf. The activity calls for fresh spinach leaves, but other leaf types may be tried.The technique is a leaf disk assay. Leaf disks are created, the air is evacuated from the disks by applying pressure and the disks are added to a cup of water.They sink. Then the disks are exposed to light and sodium bicarbonate. As photosynthesis occurs the leaf rises.