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6.2 describe the experiments, using paper chromatography, that Calvin carried out to deduce the products of photosynthesis
describe the experiments, using paper chromatography, that Calvin carried out to deduce the products of photosynthesis
- The experiments carried out by Calvin and his co-workers involved an illuminated “lollipop” in which Chlorella (unicellular photosynthetic algae) was placed. The “lollipop” was a flattened glass vessel, the shape of a large lollipop on a stick, wide but thin. The algae were given a pulse of radioactive carbon dioxide (14CO2), injected into a stream of air containing non-radioactive CO2 for a suitable period.
- Samples of the Chlorella were then released at intervals (3, 5, 10 seconds and then 15 second periods) into boiling alcohol to stop the progress of 14C at different moments in the metabolic pathway for the synthesis of glucose. Compounds that the radioactive carbon had reached at a particular moment were determined by two dimensional paper chromatography and autoradiography.
- Each sample was separated using paper chromatography (see 9.9 Biochemistry: 3. The discovery of the chloroplast as the site of photosynthesis) and the components identified. Placing the chromatogram over a sheet of X-ray film identified those that contained the 14C. The radioactivity exposed the film and so the movement of the 14C could be traced (linked to various compounds over time).