Write about the main chemical changes which occur
during photosynthesis in light and dark reactions.

Dear student
Light reactions of photosynthesis directly depends on light. The pigments absorb light energy to produce ATP and NADPH. It includes, Light absorption Water splitting Oxygen release Formation of ATP and NADPH, which is then used in the biosynthetic phase. 

Dark reaction or light independent reaction of photosynthesis utilize ATP and NADPH produced from light reactions are used for synthesising the carbohydrate (glucose). CO2 is fixed to form CO2 fixation product. The reaction involved in the biosynthetic phase takes place in the stroma of chloroplasts.

Regards