Melvin Calvin (1954) traced the path of carbon during photosynthesis and identified the first stable product of C3 cycle or Calvin cycle i.e., 3-phosphoglyceric acid. The techniques used for studying different steps were radioactive tracer technique using 14C chromatography and autoradiography and the material used were Chlorella and Scenedesmus. These are microscopic, unicellular algae and can be easily maintained in laboratory.