In Pursuit of a Pathway (1843–1918)
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The first attempts at reconstructing the mechanism of photosynthesis were made by nineteenth-century German chemists, including such eminent figures as Justus Liebig, Adolf Baeyer and Emil Erlenmeyer. None of them worked on photosynthesis for a long time—the period is characterised by “research opportunism”: most players provided only a single paper, from their respective background, and then returned to their original research area. This situation led to a striking pluralism of alternatives, which is somewhat surprising, given the deplorable state of methods and the lack of empirical data about cell processes. Closer analysis reveals that most of these models relied on an extensive transfer of knowledge from inorganic chemistry to photosynthesis (which was heavily criticised by plant scientists). Highly popular was the import of “modules”: that is, sequences of reaction steps to some specific effect, such as the reduction of carbon dioxide, were integrated in new model suggestions. This pluralism was a reaction to the complexity of the question and a strategy to keep the field as open as possible. The chapter closes with the 1918 model presented by Richard Willstätter and Arthur Stoll, which successfully merged the most promising modules and became the standard for many years to come. Photosynthesis, henceforth, was conceived of as the splitting of carbon dioxide in a complex binding with chlorophyll molecules and the subsequent reduction of the remaining carbon moiety via formaldehyde.