CO2 is the main raw material for making sugar. The amount of CO2 in the atmosphere is 0.04%. 1% of this CO2 is used in photosynthesis. Chemical reactions of water and CO2 occur in chloroplasts to produce sugars. The rate of photosynthesis increases when the amount of CO2 increases up to a certain limit. However, if the amount of CO2 is high, photosynthesis stops.