In the Real World
History and Photosynthesis
In the 1600s, Jan Van Helmont made a reasonable hypothesis. He gathered that, in order for a tree to grow and gain mass, it must obtain food from somewhere else. He carefully weighed a tree and the soil that the he wanted to plant the tree in. Time passed, and the tree grew. After five years, he reweighed the tree, which had grown quite large, and then…wait for it…he weighed the soil. To his surprise, the soil weighed basically the same amount every day. Jan concluded that the tree must have gained the nutrients from the water that he had added over the years.
Jan was partially correct: water, as well as carbon dioxide and light, are required for photosynthesis. About 100 years later, another Jan, Jan Ingen-Housz, demonstrated that plants, well actually, only the green parts like the stems and leaves, could manufacture oxygen by using the Sun’s light and not its heat. Furthermore, Jan #2 proposed the novel idea that plants used carbon dioxide (CO2) while producing oxygen (O2).1 Then, in 1881, Theodor Engelmann discovered that photosynthesis occurs in the chloroplast.
Until the 1930s, the O2 produced from photosynthesis was believed to originate from CO2. L.B. Niel, a graduate student at Stanford University at the time, hypothesized that the O2 produced during photosynthesis came from H2O rather than from CO2. It was all well and good to suggest something like that, but it was not an easy hypothesis to test. The key was that scientists had to be able to distinguish whether the O2 came from CO2 or H2O. In 1941, two scientists named Samuel Ruben and Martin Kamen did just that and showed that the O2 released during photosynthesis came from H2O. How did they do it? We know; the suspense is killing you. They made use of isotopes, or chemical elements that have the same number of protons as the regular element, but a different number of neutrons. These two geniuses also discovered 14C, an isotope of carbon, which has since been extensively used to carbon date fossils and ancient artifacts.
Since then, photosynthesis has remained an active area of research. Overall, ten Nobel Prizes in Chemistry have been given for work related to photosynthesis. Robert Huber and colleagues won the Nobel Prize in 1988 for uncovering the structure of the photosynthetic center, a discovery that Robert Huber describes as "switching on the light" of photosynthesis.6 Discovering the structure of the photosynthetic machinery gave scientists better insight into how these photosynthetic reactions were actually occurring.
Four years later, R.A. Marcus won a Nobel Prize for his work on the electron transport chain. He described his work:
"The lay person may not recognize, as I did not recognize in mathematics until I spent a year or more at a mathematical institute, that the beauty which a scientist can experience after deriving a simple equation or executing an incisive experiment is as real as that which the artist may experience in creating a work of art. I believe, too, that there are many analogies between the sport of skiing, which I dearly love, and doing theoretical work in science—the challenge and sense of excitement when the slope is a little more difficult than one feels comfortable with, or the boredom if too easy, or the probable disaster if too difficult."
- Rudolph A. Marcus
A Nobel Timeline
Here is a list of all the people who have been lucky enough to receive a Nobel Prize (forget the fame...you get $1.4 million dollars!) for work directly related to photosynthesis:
1915: Richard Martin Wilstätter "for his researches on plant pigments, especially chlorophyll"
1930: Hans Fischer "for his researches into the constitution of haemin and chlorophyll and especially for his synthesis of haemin"
1937: Paul Karrer "for his investigations on carotenoids, flavins and vitamins A and B2" and Walter Haworth "for his investigations on carbohydrates and vitamin C"
1938: Richard Kuhn "for his work on carotenoids and vitamins"
1961: Melvin Calvin "for his research on the carbon dioxide assimilation in plants"
1965: Robert Burns Woodward "for his outstanding achievements in the art of organic synthesis"
1978: Peter Mitchell "for his contribution to the understanding of biological energy transfer through the formulation of the chemiosmotic theory"
1988: Harmut Michel, Robert Huber, and Johann Deisenhofer "for the determination of the three-dimensional structure of a photosynthetic reaction centre"
1992: Rudolph Marcus "for his contributions to the theory of electron transfer reactions in chemical systems"
1997: Paul Boyer, John Walker, and Jens Skou "for their elucidation of the enzymatic mechanism underlying the synthesis of adenosine triphosphate (ATP)"
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