Dark reaction in photosynthesis is called so because
Biosynthetic phase catalyses assimilation of CO2 to carbohydrates. The reactions are known as carbon reactions. They occur in the stroma of chloroplasts. The reactions do not require light. Instead assimilatory power (ATP and NADPH) produced during photochemical phase is used in fixation and reduction of CO2. All the enzymes required for the process are present in the matrix or stroma of the chloroplast.