Undoubtedly, the process of photosynthesis is one of the most important processes for life on Earth. It is the fundamental base for our food chain. To review, plants use the sun’s light to create the energy they need to grow, which provides energy for herbivores, who then in turn become a source of energy for carnivores. Photosynthesis is the base for all of this to occur. In the NGSS this is a high school and middle school standard, but the subject of photosynthesis is often brought up in 4th and 5th grade classrooms.
Such a fundamental process is important for students to understand, both the process and its place in our energy chain. The trouble with teaching photosynthesis is that it is fundamentally an invisible phenomenon and cannot be seen. This activity will help educators turn the invisible visible so that students of all ages can see photosynthesis in action. All of the materials are common household objects. Chances are that you might have everything you need already in your kitchen to run this demonstration.
To start, take a large clear container, about 1 liter in size, and fill it with 750 mL of water. Add some baking soda to the water and allow it to dissolve. This step will create some carbon dioxide in the water which is needed for photosynthesis to occur.
Next, take some spinach leaves and create small pieces of leaves for this activity. The best way to do this is actually with an office hole punch, but you can do this with a kitchen knife as well. Cut or punch about a dozen pieces of spinach and put them into the container with the water. They will sink to the bottom of the container as they are missing one key element for photosynthesis, light.
Putting your water and leaf containing mixture under light will give the leaf pieces the final material needed to start photosynthesis. Under bright light, the leaf pieces will be able to take water and carbon dioxide and convert them into sugar and oxygen. The equation for photosynthesis that shows this is:
6CO2 + 6H2O → C6H12O6 + 6O2
The equation shows exactly what is occurring in the container; six molecules of carbon dioxide are reacting with six molecules of water to create six molecules of water and one molecule of sugar. The sugar is essential to the plant, this is the energy that it uses to repair damaged leaves and grow new branches and leaves and even fruits.
As the leaf pieces gather light, they will begin to create oxygen which will be visible in two different ways: You will see little bubbles in the container and you will see the leaf pieces begin to float. As the oxygen is created, some of the bubbles release from the leaf, and other oxygen bubbles stay attached to the leaf, giving it the buoyancy needed to float to the water’s surface. The more light hits the leaf pieces, the more oxygen is created.
As you watch this demonstration there are a few experimental variables you can change to see what happens. Since light is a crucial part of photosynthesis, you can turn off the light to see what happens to the leaf pieces if they do not have light. You can also adjust the amount of carbon dioxide present in the first step or the amount of light given to the leaf pieces. Finally, try different green leaf pieces to see how they photosynthesize.