The light-dependent reactions take place in the membranous sections of the chloroplast - thylakoids (granae/lamellae) - which offer a large surface area to absorb light energy. Do not confuse NADP with NAD which is a similar molecule involved in respiration. The main function of these reactions is to provide a source of ATP and reduced NADP, which are used to reduce CO2 in the light independent reactions. There are two photosystems consisting of chlorophyll and associated molecules.