How Priestley Ingenhousz and Sachs Proved Photosynthesis
Photosynthesis is a process by which plants produce their food. It is a photochemical process in which the light energy is absorbed by the plants and is converted into chemical energy to produce oxygen. This process was followed by the plants for ages. But it’s discovery and identification were done only in 1800 and several scientists conducted many different types of experiments to prove the existence of photosynthesis.
Photosynthesis Discovery – Early Experiments
The process of photosynthesis is carried by some of the required raw materials like water, carbon dioxide, and cellular components like plastids. Plants make use of these raw materials to synthesize carbohydrates in the presence of sunlight. These key features of photosynthesis were revealed during the mid-nineteenth century.
Some of the experiments that were conducted by the early scientists to explore photosynthesis in a better way are -
Experiment to Prove the Importance of Carbon Dioxide in Photosynthesis
Materials Required: A healthy potted plant, a wide-mouthed glass bottle with a split cork, potassium hydroxide solution (KOH), and starch solution.
Experiment:
Take a healthy potted plant and keep it in the darkroom for two to three days to ensure leaves are free from starch.
In a wide-mouthed glass bottle add 10-15 ml of potassium hydroxide solution and split the cork vertically.
Now minutely, insert half part of a leaf into a glass bottle through the split cork and the other half exposed to air.
Place the complete unit undisturbed in sunlight for about 3 – 4 hours.
Remove the leaf after 4 hours from the plant and slowly remove it out from the bottle and test it with the starch solution.
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 surroundings became dark brown indicating the presence of starch in it.
Conclusion: In this experiment, we can conclude that carbon dioxide is essential for photosynthesis. Both portions of 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.
Later, many improvised experiments were conducted by scientists to analyze the essential components for photosynthesis. Joseph Priestley (1733-1804) was the first scientist amongst others to carry out these experiments.
Experiment by Joseph Priestley
After conducting a series of experiments in 1770, Joseph Priestley concluded that the essentiality of air for photosynthesis and also for the growth of plants.
Materials Required: A candle, rat, a bell jar, and a plant.
Experiment:
Firstly, a burning candle and a rat were kept together in the single bell jar.
After some time, the candle extinguished and the rat died.
For the second time, he kept a burning candle, rat, and a green plant all together in the bell jar.
He observed that neither the candle got extinguished, nor did the rat die.
Conclusion: Based on his observations, the scientist Priestley concluded that in the first case, the air in the bell jar got polluted by the candle and the existence of the rat. However, in the second case, the plant restored the air that was spoiled by the candle and the rat. But this function of the plants was not revealed quite soon by scientists.
Other Experiments
Scientist Jan Ingenhousz also conducted experiments using the same set-up but the twist was the presence of sunlight that was highlighted as being an essential product for plants to refresh the air that was polluted by the candle or rat.
Jean Senebier came to a conclusion which said that plants absorb carbon dioxide and release oxygen during photosynthesis.
Julius Robert Mayer demonstrated that plants convert light energy into chemical energy.
Later, Julius von Sachs revealed that glucose was produced by plants.
T.W Engelmann discovered the role of chlorophylls and Cornelius van Niel uncovered that the release of oxygen by plants is from water (H2O), not from carbon dioxide. He also gave the general photosynthesis equation.
An outline was drawn for the process of photosynthesis by scientists. They concluded that light is essential for photosynthesis, and plants use carbon dioxide and water for the preparation of glucose (carbohydrate), where water molecules are the hydrogen donors and oxygen (O2) is the by-product of this biological process.
FAQs on Early Experiments on Photosynthesis and Their Discoveries
1. What were the early experiments on photosynthesis?
Early experiments on photosynthesis were scientific investigations that demonstrated how plants produce food using light, carbon dioxide, and water. Key early experiments include:
- Jan Baptista van Helmont’s experiment showing plant mass comes mainly from water.
- Joseph Priestley’s experiment proving plants restore air made impure by burning candles.
- Jan Ingenhousz’s experiment showing light is essential for oxygen release.
- Julius von Sachs’ experiment demonstrating starch formation in green parts of plants.
2. What did Jan Baptista van Helmont discover about photosynthesis?
Jan Baptista van Helmont discovered that plant growth largely depends on water rather than soil mass. In his classic willow tree experiment:
- He planted a sapling in a weighed amount of soil.
- After 5 years, the plant gained significant weight.
- The soil weight changed very little.
3. How did Joseph Priestley contribute to the discovery of photosynthesis?
Joseph Priestley showed that plants can restore air that has been made impure by burning candles. In his experiment:
- A candle placed in a closed jar went out.
- A mouse in a sealed jar died.
- When a green plant was added, the candle could burn again.
4. What did Jan Ingenhousz prove about light and photosynthesis?
Jan Ingenhousz proved that light is necessary for photosynthesis to occur. He observed that:
- Green plants released bubbles only in the presence of sunlight.
- No oxygen was released in the dark.
- Only green parts of the plant produced oxygen.
5. What was the role of Julius von Sachs in understanding photosynthesis?
Julius von Sachs demonstrated that photosynthesis produces starch in green parts of plants. His experiment involved:
- Exposing a leaf to sunlight.
- Testing it with iodine solution.
- Observing blue-black coloration in light-exposed areas.
6. How was the role of chlorophyll discovered in early photosynthesis experiments?
The role of chlorophyll was discovered when scientists observed that only green parts of plants carry out photosynthesis. Experiments showed that:
- Non-green areas of variegated leaves did not produce starch.
- Green areas containing chlorophyll tested positive for starch.
7. What is the importance of the variegated leaf experiment in photosynthesis?
The variegated leaf experiment proved that chlorophyll is necessary for photosynthesis. In this experiment:
- A variegated leaf (with green and non-green regions) was exposed to light.
- The leaf was tested with iodine for starch.
- Only the green regions turned blue-black.
8. How did scientists prove that carbon dioxide is required for photosynthesis?
Scientists proved that carbon dioxide is required for photosynthesis using experiments that removed CO₂ from the environment. In a classic setup:
- A plant was placed in a sealed jar with potassium hydroxide (KOH) to absorb CO₂.
- Another plant was kept in normal air as a control.
- The CO₂-deprived plant did not form starch.
9. What did early experiments reveal about the products of photosynthesis?
Early experiments revealed that the main products of photosynthesis are oxygen and carbohydrates. Evidence showed that:
- Oxygen is released in the presence of light.
- Starch accumulates in green leaves.
10. Why are early experiments on photosynthesis important in biology?
Early experiments on photosynthesis are important because they established the scientific basis of how plants make food and release oxygen. These experiments:
- Identified the role of light, water, and carbon dioxide.
- Proved that oxygen is a by-product.
- Showed that photosynthesis occurs in chlorophyll-containing tissues.
