Floating Spinach Disks Photosynthesis Demonstration

Watch spinach leaf disks rise  and fall in a baking soda solution in response to photosynthesis. The leaf disks intake carbon dioxide from a baking soda solution and sink to the bottom of a cup of water. When exposed to light, the disks use carbon dioxide and water to produce oxygen and glucose. Oxygen released from the leaves forms tiny bubbles that cause the leaves to float. Photosynthesis Demonstration Materials You can use other leaves for this project besides spinach. Ivy leaves or pokeweed or any smooth-leaf plant work. Avoid fuzzy leaves or areas of leaves that have large veins. fresh spinach leavessingle hole punch or a hard plastic strawbaking soda (sodium bicarbonate)liquid dishwashing detergentplastic syringe (no needle, 10  ccs or larger)clear cup or glasslight source (bright sunlight works or you can use an artificial light) Procedure Prepare a bicarbonate solution by mixing 6.3 grams (about 1/8 teaspoon) baking soda in 300 milliliters of water. The bicarbonate solution acts as a source of dissolved carbon dioxide for photosynthesis.In a separate container, dilute a detergent solution by stirring a drop of dishwashing liquid in about 200 milliliters of water.Fill a cup partly full with the baking soda solution. Add a drop of the detergent solution to this cup. If the solution forms suds, add more baking soda solution until you stop seeing bubbles.Use the hole punch or straw to punch ten to 20 disks from your leaves. Avoid the edges of the leaves or major veins. You want smooth, flat disks.Remove the plunger from the syringe and add the leaf disks.Replace the plunger and slowly depress it to expel as much air as you can without crushing the leaves.Dip the syringe in the baking soda/detergent solution and draw in about 3 ccs of liquid. Tap the syringe to suspend the leaves in the solution.Push the plunger to expel e xcess air, then place your finger over the end of the syringe and pull back on the plunger to create a vacuum.While maintaining the vacuum, swirl the leaf disks in the syringe. After 10 seconds, remove your finger (release the vacuum).You may wish to repeat the vacuum procedure two to three more times to ensure the leaves take up carbon dioxide from the baking soda solution. The disks should sink to the bottom of the syringe when they are ready for the demonstration. If the disks do not sink, use fresh disks and a solution with a higher concentration of baking soda and a bit more detergent.Pour the spinach leaf discs into the cup of baking soda/detergent solution. Dislodge any disks that stick to the side of the container. Initially, the disks should sink to the bottom of the cup.Expose the cup to light. As the leaves produce oxygen, bubbles forming on the surface of the disks will cause them to rise. If you remove the light source from the cup, the leaves eventually will sink.If yo u return the disks to the light, what happens? You can experiment with the intensity and duration of the light and its wavelength. If you would like to set up a control cup, for comparison, prepare a cup containing water with diluted detergent and spinach leaf disks that have not been infiltrated with carbon dioxide.