The Biology Project > Biochemistry > Introduction to Photosynthesis >

Light Independent Process


The light independent process (also called dark reactions or the Calvin-Benson cycle) takes place in the stroma of the chloroplast. Carbon dioxide is modified by series of chemical reactions to form carbohydrates. The energy for these reactions comes from ATP and NADPH generated during the light dependent process.

Animation (120 K)


Carbon fixation, the incorporation of carbon dioxide into an organic molecule, is the first step of the light independent process. To form one molecule of glucose, 6 molecules of CO2 bind with Ribulose Bisphosphate (RuBP). This reaction is catalyzed by the enzyme ribulose biosphosphate carboxylase/oxidase (RUBISCO). Twelve molecules of 3-Phosphoglycerate (3PG) are the products of this reaction.

Energy from ATP and NADPH reduce the 3PG molecules to form another 3 carbon compound, glyceraldehyde-3-phosphate (G3P). Two G3P molecules are removed from the cycle and ultimately become one glucose molecule. The other 10 molecules of G3P are converted back to RuBP molecules, ready to accept CO2 and start the cycle again.


Overview | Food Web | Leaf Structure | The Chloroplast | Pigments | Oxygen

Light Dependent Process | Light Independent Process

Problem Set

The Biology Project > Biochemistry > Introduction to Photosynthesis >