C₄ cycle is

The C₄ cycle is an Adjunct to the Calvin cycle.
C₄ carbon fixation is one of three known photosynthetic processes of carbon fixation in plants.
The CO₂ in C₄ cycle is fixed by RuBisCo to produce phosphoglycerate (PGA) while the pyruvate is transported back to the mesophyll cell, together with about half of the phosphoglycerate.
This PGA is chemically reduced in the mesophyll and diffuses back to the bundle sheath where it enters the conversion phase of the Calvin cycle.