Conversely, indirect photolysis is effected when O2 and H2 production are separated by time:
oxygenic photosynthesis activity is decreased or inhibited, whereas mitochondrial respiration remains unchanged, consuming the O2 present. Under such conditions, there is a net consumption of O2 by the cells, establishing the anaerobic conditions required to express the O2-sensitive hydrogenase and to carry out H2 production.