Assimilatory power in photosynthesis refers to ATP and NADPH2 , which are produced during light reaction of photosynthesis and are used during dark phase for assimilating CO2 to produce organic substance. Carbon assimilation occurs in stroma or matrix of chloroplast by two ways (i) Calvin cycle and (ii) Hatch and Slack pathway. ATP (Adenosine triphosphate) is a nucleotide that is of fundamental importance as a carrier of chemical energy in all living organisms. NADPH2 is reduced NADP+ which acts as hydrogen donor.