NADP is a co enzyme which acts as a hydrogen carrier. The role of NADP is to carry the hydrogen atom from the light dependent stage, which comes from the water molecule ( water molecule splits to form H+ , 2electrons & oxygen, which is a waste gas). NADP carries this hydrogen atom n gets reduced. the reducing power of reduced NADPH reduces the 3 Carbon acid tht has the grp ( -COOH )...to a 3 Carbon sugar that has an aldehyde group ( -CHO ) known as Glyceraldehyde phosphate, which is a triose phosphate. This is the first carbohydrate in photosynthesis. The reason for the conversion of GP to TP is because TP contains more chemical energy.