Assertion (A) : Within the chloroplast, membranes are sites for light reactions while biosynthetic pathways occur in stroma
Reason (R) : Thylakoids contain photopigments and trap light energy;RuBiSCo enzyme is present in stroma.

There is a clear division of labor within the chloroplast. The membrane system, (thylakoids-grana) is responsible for trapping the light energy and also for the synthesis of ATP and NADPH. In stroma, (the liquid phase) enzymatic reactions synthesize sugar, which in turn forms starch.