8.3 Photosynthesis

Developments in scientific research follow improvements in apparatus—sources of 14C and autoradiography enabled Calvin to elucidate the pathways of carbon fixation.

At the beginning of the 20th-century, the scientific understanding of photosynthesis was centred on the combination of Carbon Dioxide with chlorophyll to produce formaldehyde as an intermediate before being converted to a carbohydrate (Benson). This view predominated up to the discovery of radioactive Carbon-14 by Kamen and Benson in 1940 (Benson).

In 1945, C14 became readily available to researchers in the US. A young researcher in California, Melvin Calvin, was told by a senior scientist at the University of California-Berkley that he should start to do something interesting with it. So began a research focus that led to the Nobel Prize in Chemistry in 1961 “for his research on the carbon dioxide assimilation in plants” (“Melvin Calvin-Facts”).

The shape of the apparatus Calvin used led to it being called the “lollipop” experiment. The central “lollipop” contained a suspension of algae, to which was introduced the radioactive carbon.  Periodically, a sample of the algae was released into the tube below (the stick of the lollipop) where it was immediately killed by a solution of alcohol.  The compounds could then be analysed through chromatography.  By using the radioactively labelling isotope of carbon, it was possible to trace the path the isotope took and by analysing the intermediate compounds the researchers were able to determine what happened to the carbon – where was it absorbed and what was it used for? The series of experiments helped identify the sequence of carbon compounds produced in the Calvin Cycle and also disproved the idea that chlorophyl fixes carbon.

Lollipop PS
The “Lollipop” apparatus (The Bancroft Library)

These experiments were carried out be many individuals over a period of nearly 15 years and in some ways it seems unfair that Calvin tends to receive all the credit (as well as a solo Nobel Prize). A personal report by Andrew Benson (available here) gives a good idea of the collaborative nature of this process.


Benson, A. Following the path of carbon in photosynthesis: a personal story. Photosynthesis Research. 73: 29–49, 2002. Web. April 20, 2016.

Calvin, Melvin. “The Path of Carbon in Photosynthesis.” Nobel Lectures, 1964, pp. 618–644., http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1961/calvin-lecture.pdf. Web. 30, Jan. 2018

“Calvin’s Lollipop Experiment.” The Bancroft Library, The University of Berkeley, California, bancroft.berkeley.edu/Exhibits/Biotech/Images/3-9lg.jpg. Web. Jan 30, 2018.

“Melvin Calvin – Facts”. Nobelprize.org. Nobel Media AB 2014. Web. 19 Apr 2016.



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