Carbon dioxide diffuses into the cell leaf through the stomata, and diffuses into the water surrounding the mesophyll cell walls (main site of photosynthesis-packed with many chloroplasts). From here, the carbon dioxide then diffuses through the mesophyll cell wall and cell membranes, and through the chloroplast cell membrane into the stroma (chloroplast cyptoplasm). The carbon dioxide combines with a 5 carbon-compound RuBP (ribulose biphopshate) to produce 2 x 3 carbon compound GP (glycerate 3 phosphate). This process is catalysed by the enzyme RuBisco. Reduced NADP from the light dependent reaction is used to reduce (gain of protons) GP to TP (triose phosphate) using energy supplied by ATP. Majority of the TP is used to produce glucose, amino acids etc. However, the majority of TP is converted back into RuBP.