An account of the author's life and scientific research is presented. Two main lines of research have been pursued: (1) Studies on the physiological aspect of photosynthesis started from experiments with crops under field conditions and then extended to the study of photosynthesis in nature; and (2) studies on the mechanism of photophosphorylation and related problems which began with the measurement of quantum requirement of photophosphorylation. This work led to the discovery of the 'high energy state' of phosphorylation and many other interesting findings. In recent years, efforts have been made to study the operation and regulation of photosynthetic apparatus with a view to link the above-mentioned lines of research together.