Before seventeenth century it was considered that plants take their food from the soil.
- Van Helmont (1648) concluded that all food of the plant is derived from water and not from soil.
- Stephen Hales (Father of Plant Physiology) (1727) reported that plants obtain a part of their nutrition from air and light may also play a role in this process.
- Joseph Priestley (1772) demonstrated that green plants (mint plant) purify the foul air (i.e., Phlogiston), produced by burning of candle, and convert it into pure air (i.e., Dephlogiston).
- Jan Ingen-Housz (1779) concluded by his experiment that purification of air was done by green parts of plant only and that too in the presence of sunlight. Green leaves and stalks liberate dephlogisticated air (Having \[{{O}_{2}}\]) during sunlight and phlogisticated air (Having \[C{{O}_{2}}\]) during dark.
- Jean Senebier (1782) proved that plants absorb \[C{{O}_{2}}\]and release \[{{O}_{2}}\] in presence of light. He also showed that the rate of \[{{O}_{2}}\] evolution depends upon the rate of \[C{{O}_{2}}\]consumption.
- Nicolus de Saussure (1804) showed the importance of water in the process of photosynthesis. He further showed that the amount of \[C{{O}_{2}}\]absorbed is equal to the amount of \[{{O}_{2}}\] released.
- Julius Robert Mayer (1845) proposed that light has radiant energy and this radiant energy is converted to chemical energy by plants, which serves to maintain life of the plants and also animals.
- Liebig (1845) indicated that main source of carbon in plants is \[C{{O}_{2}}.\]
- Bousingault (1860) reported that the volume of \[C{{O}_{2}}\] absorbed is equal to volume of \[{{O}_{2}}\] evolved and that \[C{{O}_{2}}\] absorption and \[{{O}_{2}}\] evolution get start immediately after the plant was exposed to sunlight.
- Julius Von Sachs (1862) demonstrated that first visible product of photosynthesis is starch. He also showed that chlorophyll is confined to the chloroplasts.
- Melvin Calvin (1954) traced the path of carbon in photosynthesis (Associated with dark reactions) and gave the \[{{C}_{3}}\] cycle (Now named Calvin cycle). He was awarded Nobel prize in 1961 for the technique to trace metabolic pathway by using radioactive isotope.
- Huber, Michel and Deisenhofer (1985) crystallised the photosynthetic reaction center from the purple photosynthetic bacterium, Rhodopseudomonas viridis. They analysed its structure by X-ray diffraction technique. In 1988 they were awarded Nobel prize in chemistry for this work.
