PHOTOSYNTHESIS: History of Discoveries

• Ancient Greeks: The Greeks believed that plants derived their nourishment from the soil only

Jan van Helmont (early 1600s) After careful measurements of a plant’s

water intake, and weight increase, van Helmont concludes that trees gain most of their mass from water.

British ScientistJoseph Priestly (1771)

Using a bell jar, a candle, and a plant (peppermint sprig), Priestly finds that the plant releases a substance that keeps the candle burning—a substance that we now know is oxygen.

In the experiment the peppermint sprig restored the oxygen that was originally consumed by the candle combustion.

Dutch Scientist - Jan Ingenhousz – (1779)

He proved that Priestly's experiment only happened if light available. He experimented with aquatic plants and found that they produced oxygen bubbles only in the light, and nothing in the dark. He concluded that plants need sunlight to produce oxygen.

German Scientist - Julius Robert Mayer (1845)

He concluded that plants convert light energy to chemical energy.

chemical energy

Martin Kamen & Samual Ruben (1941) (CoDiscoverers of Carbon-14 Isotope)

These American scientists used isotopes

to determine that the oxygen that was liberated from photosynthesis comes from water.

American Scientist - Melvin Calvin –(1948) He traced the chemical path that carbon

follows to form glucose. The reactions became known as the “Calvin cycle.” (a.k.a. light independent reactions)

1992 American Scientist - Rudolph Marcus He won the Nobel Prize in Chemistry for

describing the process by which electrons are transferred from one molecule to another in the electron transport chain.

In Summary…

• These scientists & others revealed the facts about photosynthesis.

• Plants transform carbon dioxide & water into carbohydrates, and release oxygen.