Historical Events in Photosynthesis

Photosynthesis was worked out gradually, across more than three centuries, and each generation of scientists corrected or extended the previous one's picture. Van Helmont (1648) grew a willow tree in a weighed pot for five years and found the tree had gained a huge amount of weight while the soil lost only about 2 ounces - he wrongly concluded that water alone built the tree, but he was the first to show that soil is not the main source of plant substance. Stephen Hales (1727), later called the Father of Plant Physiology, proposed that plants draw nourishment from air and light, not only from soil. Joseph Priestley (1772) used candle, mouse and mint-plant experiments to show that vegetation "purifies" air that had been fouled by burning or breathing, and Jan Ingenhousz (1779) confirmed that this purifying effect - oxygen release - only happens in light, not in darkness. Lavoisier (1783) identified and named the two gases involved, oxygen (the purifying gas released in light) and carbon dioxide (the noxious gas from burning). De Saussure (1804) established how essential water is to the process, and Dutrochet (1837) established chlorophyll's central role. Von Mayer (1845) framed photosynthesis correctly for the first time as solar energy being converted into the chemical energy of organic matter, while Liebig (1845), in the same year, showed that a plant's organic matter is built from CO2. Julius von Sachs (1854) discovered that starch is photosynthesis's first visible product and pinpointed chlorophyll's location inside chloroplasts. Engelmann (1888) was the first to plot an action spectrum of photosynthesis. Blackman (1905) proposed the Law of Limiting Factors (elaborated in section 13.17). Warburg (1920) established the green alga Chlorella as a standard experimental organism for photosynthesis research. Van Niel (1931), working with purple and green sulphur bacteria, showed that the oxygen released during photolysis comes from water, not from CO2, and wrote a generalised equation, 2H2A + CO2 to (CH2O)n + H2O + 2A, that covers both plants (where A = O, from water) and sulphur bacteria (where A = S, from H2S, so sulphur rather than oxygen is released). Emerson and Arnold (1932) used flashing-light experiments to demonstrate that photosynthesis genuinely has separate light and dark phases. Robert Hill (1937) showed that isolated chloroplasts, given a suitable electron acceptor, evolve oxygen and reduce that acceptor in light even with no CO2 present (section 13.7.3). Ruben and Kamen (1941) used radioactive 18O-labelled water to prove definitively that the oxygen evolved in photosynthesis originates from water. Arnon, Allen and Whatley (1954) used radioactive 14CO2 to show that isolated chloroplasts alone can fix CO2. Melvin Calvin (1954-57), together with Andrew Benson, used the same radioactive-tracer approach to trace the path of carb …