Introduction: Photosynthesis in a Beaker

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6H2O + 6CO2 + Light Energy ----------> C6H12O6 + 6O2

This is one of the equations that are most important for our existence on earth. This equation is the representation of the chemical reaction that takes place during photosynthesis in plants.

Basically, photosynthesis is the process by which plants convert the sun's light into energy. Photosynthesis is one of the most important processes on this planet; it is the foundation for the entire food chain and provides humans with breathable air.

In this project, we will conduct a simple experiment using spinach leaves to demonstrate that, in the presence of light and carbon dioxide, leaves produce gas bubbles. While we cannot prove in this experiment that these bubbles are oxygen without a gas probe, but when we investigate further and perform this experiment in the absence of baking soda(sodium bicarbonate), which provides carbon dioxide, no bubbles are released.

Supplies

  1. A clear drinking glass or 500ml beaker
  2. A saucer plate or a petri dish
  3. 10 ml syringe without needle
  4. Bowl
  5. Spoon
  6. Liquid dish
  7. Fresh Spinach leaves
  8. Baking soda

Step 1: Preparation

Cut 10-15 small pieces of spinach leaves and put them in the saucer/petri dish.

Pour some water into the bowl and add few drops of liquid dish soap to it. Stir the solution gently to prepare a liquid soap solution.

Mix 2-3 grams of baking soda (Sodium bicarbonate) and 1.5 cups of water into the beaker.

Step 2: Procedure

With the help of the spoon, pour some liquid soap solution into the beaker. Stir the solution to mix it well.

Remove the plunger from the syringe and drop the spinach pieces inside. Replace the plunger back and push the plunger almost to the bottom but make sure not to crush the leaves.

Now, draw 7 ml of the soda-soap solution from the beaker. The leaves will float in the solution.

Hold/point the syringe upward. Tap the syringe to release any trapped air bubble between the leaf pieces and gently push the plunger to expel air from the syringe.

Blocking the tip of the syringe with the thumb, draw the plunger back slightly, creating a partial vacuum. Hold the plunger for 3 seconds before releasing it. Repeat this until all the leaves sunk to the bottom of the solution in the syringe. This action forces the liquid into the interior of the leaf expelling air out of the leaves.

Next, pour the content of the syringe into the beaker. Try to keep the disks from sticking to each other or the sides of the cups and let them sit properly. Remove any floating leave from the beaker.

Place the beaker/glass cup in an open place with ample sunlight.

Step 3: Results

In the sunlight, after few minutes we'll notice tiny bubbles forming around the edges of the leaf pieces. As time passes more and more bubbles forms around the leaves, which causes the leaves to rise up to the top of the solution and float.

Step 4: ​Explanation

In simple terms, during photosynthesis, plants take in carbon dioxide (CO2) and water (H2O) from the air and soil and convert them to glucose and oxygen, in the presence of sunlight and chlorophyll. The plant then releases the oxygen back into the air, and stores energy in the form of glucose molecules.

Now, in our setup, all the components necessary for photosynthesis are present. Chlorophyll is already present in the spinach leaves, the solution provides water, and baking soda provides dissolved carbon dioxide. So when we place the beaker in sunlight, the setup receives the light energy which initiates the chemical reaction.

The air bubbles that we observe around and under the leaves are actually oxygen(O2) gas produced as a byproduct of the chemical reaction. Over time this accumulation of oxygen bubbles around the leaves causes the leaves to float to the top of the solution.

Step 5: Investigating Further

Encourage students to change the factors that affect photosynthesis and check how long does it take for the leaves to float under different conditions.

Here are some probing questions you may ask students to keep the ball rolling.

  1. Why does the suction help the leaves to sink?
  2. Why it takes longer for the first leaf to float?
  3. How does the change in concentration of soap and baking soda solution affect the rate of photosynthesis?
  4. What will be the rate of photosynthesis, if we perform this experiment with normal water(without adding soap-soda solution).
  5. After all(or most) leaves have floated to the top of the solution, what will happen if we keep the beaker in a dark room?
  6. How does the intensity of light affect the rate of photosynthesis?
  7. Does the experiment work if we keep the beaker under artificial light instead of sunlight?

Students may also plot the "Number Of Floating Leaves vs Time(minutes)" graph to check and compare their results under different conditions.