Most of the enzymes that catalyze the reactions of CO2 fixation are in the stroma of the chloroplast, where those reactions take place. These enzymes use the energy in ATP and NADPH to reduce CO2 to carbohydrates. Therefore, with some exceptions, CO2 fixation occurs only in the light, when ATP and NADPH are being generated.
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The Calvin cycle describes the chemical steps that produce carbohydrates from carbon dioxide in the stroma of the chloroplast.
Light affects photosynthetic carbon fixation.