Final answer:
CO2 and H2O are stored in the stroma of the chloroplast before being used in photosynthesis.
Step-by-step explanation:
Before CO2 and H2O are used in photosynthesis, they are stored in the stroma of the chloroplast. The stroma is the liquid-filled space surrounding the thylakoid membranes, where the light-independent reactions of photosynthesis take place. The thylakoid membranes, on the other hand, are responsible for the light-dependent reactions of photosynthesis.