The atmospheric carbon dioxide is captured by an enzyme called RuBisCo that catalyses the reaction between CO2 and ATP and NADPH.
3 CO2 + 9 ATP + 6 NADPH + 6 H+ → C3H6O3-phosphate + 9 ADP + 8 Pi + 6 NADP+ + 3 H2O
ā3-carbon phosphate sugar is formed that combines to form starch and carbohydrates.