A 2-week or longer investigation for grades 9-12.
The photosynthesis investigation can be adapted to a variety of levels, depending on which resources fit the students.
Leaves are the primary photosynthetic organs in plants. Much of the internal volume of a leaf consists of air spaces that are necessary for gas exchange. The principle of leaf disk flotation is to remove the air from these intercellular spaces, a process called infiltration, and replace it with a bicarbonate solution that serves as a source of CO2. As photosynthesis occurs, O2 is produced which forms ever increasing bubbles trapped in the spaces. As more and more oxygen is produced, the leaf disks become buoyant and eventually float. The rate of flotation is an indirect measure of the rate of photosynthesis.
Leaf disk floatation experiments require only low cost, simple materials.