Photosynthesis - (Jun Wu)

YouTube Video

YouTube Video

Overview of activity:

It is designed for 9th to 12th graders. The principle of photosynthesis will be studied. It needs about 50 minutes.



  • Students will know that oxygen is one of the reactants for photosynthesis and carbon dioxide is one of the products of photosynthesis.


Standards: (biology/life, science content standards for grades nine to twelve)

1. a. Students know cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings.

The plasma membrane consists of two layers of lipid molecules organized


1. c. Students know how prokaryotic cells, eukaryotic cells (including those from plants and animals), and viruses differ in complexity and general structure.


1. f. Students know usable energy is captured from sunlight by chloroplasts and is stored through the synthesis of sugar from carbon dioxide.



  • young spinach leaves
  • straw
  • one 100 ml beaker and one 500ml beaker
  • 5 ml sodium bicarbonate/detergent solution
  • water
  • plastic 10-cc syringe
  • light source
  • stopwatch



    1. Use the straw to punch five disks from a spinach leaf.
    2. Fill one 100ml beaker halfway with the sodium bicarbonate / detergent solution. Fill the 500ml beaker with water.
    3. Remove the plunger from the syringe and place the spinach leaf disks into the syringe. Insert the plunger and draw 5ml of the sodium bicarbonate / detergent solution into the syringe.
    4. Hold the syringe so that the tip is pointing upwards. Push on the plunger to sqirt out any air in the syringe.
    5. Place your finger on the tip of the syringe and withdraw the plunger to form a vacuum, but be careful not to pull the plunger all the way out of the syringe. Shake the syringe a few times while your finger is on the tip.
    6. Take your finger off the tip of the syringe. This causes the leaf disks to sink to the bottom of the syringe.
    7. Place your finger over the tip of the syringe and turn it so the tip is pointing down. Carefully remove the plunger and pour the contents of the syringe into the beaker of water.

Place the beaker with leaf disks under the light source and immediately start the stopwatch. Record the time it takes for each leaf disk to float to the top of the water.

Students’ prior knowledge:

        Students know about chemical reactions. Students need to know that photosynthesis is a type of chemical reaction happening in a plant cell (chloroplast). Photosynthesis will be affected by light.



  1. Why did the leaf disk sink after you created a vacuum in the syringe?
  2. Why did the leaf disk go back up to float in the water after you put the leaf disk in water under a light source?
Norman Herr,
Nov 15, 2010, 9:35 PM