One molecule of CO2 enters a mesophyll cell via a stoma.

The CO2 that just entered the cell then reacts with PEP in the enzyme PEP carboxylase. The PEP is a 3 carbon molecule, and fixing one CO2 molecule onto it will synthesize the 4 carbon molecule, oxaloacetate.

PEP Carboxylase has no affinity for oxygen, so it will not react with it even if the oxygen is present in the cell.

Using the products of the light dependent reactions, NADPH and H+, Oxaloacetate is converted to Malate, which is also a 4 carbon molecule. This process releases NADP+ back to the light dependent reactions. This reaction is catalyzed by the enzyme malate dehydrogenase.

The Malate enters a bundle-sheath cell via a tube called plasmodesmata. This tube connects bundle-sheath and mesophyll cells.

Once in the bundle-sheath cell, the malate splits into one molecule of carbon dioxide and one molecule of pyruvate, a 3 carbon molecule. In the process, malate reduces NADP+ to NADPH with the portion left after the carbon dioxide breaks off. The carbon dioxide then enters the Calvin Cycle to complete the light independent reactions. The Calvin Cycle uses the CO₂ and refixes it using the Rubisco Enzyme. This produces 1 G3P molecule per turn, so needs 2 cycles to synthesize one molecule of glucose.

The Pyruvate is transported into the mesophyll cell via a second plasmodesmata.

The Pyruvate reacts with a molecule of ATP and an inorganic phosphate group to regenerate PEP and release Adenosine Monophosphate (AMP) and two inorganic phosphate groups as products. This reaction is catalyzed by the enzyme, phosphopyruvic dikinase.