Instrumentation and methodology were developed in the areas of mass spectrometry, sensitive spectroscopy, polarography (O exchange), and techniques for irradiating photosynthetic materials with high-intensity monochromatic light. O uptake could be decreased or enhanced during photosynthesis, depending on wavelength of illumination. Photosystem I was sensitized predominantly by long-wave illumination, with suppression of respiratory uptake. A long-wave chlorophyll component (P700) was detected in the chloroplast which occurs in the low concentration of 1/100 chlorophylls. In the primary event of photosystem I, P700, upon excitation must lose an electron to an associated reaction partner. In complete photosynthesis, the P700 is re-reduced by photosystem II. In a study with a mutant of Scenedesmus, the reducing power generated in photosystem II, simultaneous with O, was not lower than +0.18 v.