Early Experiments on Photosynthesis

Table of Contents

• Introduction
• Photosynthesis Discovery – Early Experiments
• Experiment to Prove Carbon dioxide is essential for Photosynthesis
• Other Experiments

Photosynthesis is a light-dependant process that plants use to produce their own food. It is the process by which plants convert light energy into chemical energy, which can be used later for plants’ own processes. During this process, oxygen is produced as a byproduct. Photosynthesis was discovered only in 1800. To prove the existence of photosynthesis in plants, many scientists performed numerous experiments.

Let us have a detailed look at the early experiments on photosynthesis.

Also Read: What is Photosynthesis

Since photosynthesis is a light-dependant process, it only takes place in the presence of sunlight. But along with sunlight, the plant also requires water and carbon dioxide as raw materials for this process to synthesise carbohydrates. Green plants also possess a green pigment known as chlorophyll which helps in capturing light energy. All these key features of photosynthesis were revealed later during the mid-nineteenth century when numerous scientific studies were conducted on photosynthesis.

Below mentioned are the experiments that were conducted by the early scientists in support of photosynthesis.

Materials required: A healthy potted plant, a wide-mouthed glass bottle with a split cork, potassium hydroxide solution (KOH), and starch solution.

Experiment:

1. Select a healthy potted plant and place it in the darkroom for two to three days to ensure the leaves are free from starch.
2. In a wide-mouthed glass bottle, add 10-15 ml of potassium hydroxide solution and split the cork vertically.
3. Now carefully insert half part of a leaf into a glass bottle through the split cork and the other half exposed to air.
4. Place the complete unit undisturbed in sunlight for about 3 – 4 hours.
5. After 4 hours, detach the leaf from the plant and slowly remove it from the bottle and test it with the starch solution.
6. We can observe that the half part leaf which was inside the glass bottle (KOH solution) did not show any colour change, but the other half part exposed to the surroundings turned its colour to dark brown, indicating the presence of starch in it.

Conclusion: In this experiment, we can conclude that carbon dioxide is essential for photosynthesis. Both the portion of the leaf received the same amount of water, chloroplasts, and sunlight but the half part which was inside the glass bottle did not receive carbon dioxide.

After discovering the importance of carbon dioxide in photosynthesis, many experiments were conducted to understand other essential factors for this process. Joseph Priestly was one of the first scientists to perform these experiments.

Experiment by Joseph Priestley

In 1770, after a series of experiments, Joseph Priestley came to a conclusion regarding the essentiality of air for photosynthesis and also for the growth of plants.

Materials required: A bell jar, candle, rat, and a plant.

Experiment:

1. Priestley kept a burning candle and a rat together in the single bell jar.
2. After some time, the candle was extinguished, and the rat died.
3. For the second time, he kept a burning candle, a rat, and a green plant together in the bell jar.
4. He observed that neither the candle got extinguished nor did the rat die.

Conclusion: Based on his observations, Priestley concluded that in the first case, the air in the bell jar got polluted by the candle and rat. However, in the second case, the plant reinstated the air that was spoiled by the candle and the rat.

But it took another few years to reveal what was exactly released by the plant to keep the rat alive and the candle burning.

Jan Ingenhousz: He proved that sunlight is essential for the photosynthesis process during which carbon dioxide is used and oxygen is produced.

Jean Senebier: He demonstrated that during photosynthesis, carbon dioxide in the air is absorbed, and oxygen is released by the plant.

Julius Robert Mayer: Mayer proposed the idea that light energy is being converted into chemical energy during photosynthesis.

Julius Von Sachs: He discovered that the photosynthesis process leads to the production of glucose molecules.

T.W.Engelmann: Engelmann was the scientist who discovered the importance of chlorophyll in photosynthesis.

Cornelius van Niel: He introduced the chemical equation of the photosynthesis process when he revealed that the oxygen released by plants at the end of photosynthesis comes from water and not from carbon dioxide.

Also Read: Photosynthesis in Higher Plants

To learn more about the photosynthesis discovery and early experiments on photosynthesis, keep visiting BYJU’S website or download BYJU’S app for further reference.