The best answer is Calvin cycle.
The Calvin cycle is the main mechanism by which plants convert carbon dioxide into carbohydrates. The Calvin cycle occurs in three major stages namely the carboxylation phase, reduction phase and regeneration phase in that order.
It is in the carboxylation phase that with the help of an enzyme called RuBisCo that carbon dioxide is added to a sugar called ribulose to form a 6-carbon intermediate which is then converted to 3PGA (3-phosphoglycerate)
3PGA goes through the remaining stages to finally form G3P (glyceraldehyde3 phosphate) which is then used to make carbohydrates essential to the plant such as sucrose, glucose, starch and cellulose.
