photosynthesis takes place in the mesophyllcells, but carbon fixation (and opening of stomata) takes place at night and the Calvin cycle happens during the day
The carbon fixation occurs in the stroma, which is the colourless fluid that bathes the grana inside the chloroplast. It is in the stroma that the biochemical reactions of reduction take place, one of them beingcarbon fixation. This is a light-independent reaction that is part of Calvin cycle. The stroma is where the enzymes that catalyse these reactions can be found.
