Early Experiments of Photosynthesis

Photosynthesis is a physico-chemical process. Green plants use light energy for the synthesis of organic matter like glucose. It is an enzyme regulated anabolic process. Photosynthesis is the basis of life on earth because it is the primary source of all types of  food on earth directly or indirectly. It is only a process to fix  atmospheric carbon dioxide and in turn it releases oxygen to maintain the  ecological balance. Besides carbon dioxide,

Chlorophyll, sunlight is also  required for photosynthesis .The green part of the leaf is the main site of photosynthesis.

Jan Baptista van Helmont provided a random concept that discovered the process of photosynthesis. He grew a willow tree in a weighted amount of soil. After five years, he observed that the weight of the willow tree had increased . The increase in weight of willow tree was more than his recorded data of  soil and minerals .He concluded that plant growth cannot only be due to minerals from the soil. He thought that the extra plant material had come from the water and carbon dioxide and plants accumulate some dry matter by process like photosynthesis.

Joseph Priestley demonstrated  on the basis of his experiments the essential role of oxygen in growth of green plants. He put   a mouse in a closed bell jar with a lighted candle. After that the mouse died due to  suffocation and the candle lost its light.Now he put a mint plant  in a bell jar. He observed that  neither candle will extinguish nor will the mouse die. He concluded that the carbon dioxide that was produced by animals is responsible for death of mouse and loss of light by candle. But with the mint plant, both mouse and candle remain assuming its position . He concluded that  mint plants use carbon dioxide and release oxygen. This oxygen is necessary for the burning of candles and the lives of mice. Priestley discovered Oxygen gas in 1774.

Julius Von Sachs illustrated that green parts of  plants are capable for the production of carbohydrates like glucose. That glucose  is stored in the form of reserve food  as starch. Starch is the first visible product of photosynthesis.

Theodre welhem Engelmann used a prism to split the  light into its component. In second step he placed an illuminated Cladophora placed in a suspension of aerobic bacteria. He observed  that bacteria accumulated in blue and red light of the split spectrum. He concluded that organisms use different  types of wavelengths of light on photosynthesis.

Cornelius Van Neil  stated that photosynthesis is a light dependent reaction . He  postulated that Hydrogen reduces carbon dioxide for the production of Glucose.  In greenplants water is hydrogen donor and release oxygen during photosynthesis . When he used hydrogen sulphide 

In green sulphur bacteria, 

instead of water  as hydrogen donor no Oxygen was evolved. He concluded  that oxygen  evolved by green plants comes from water  but not from carbon di oxide.