The Calvin Cycle
• The light independent reaction is also known as the Calvin Cycle
• The reaction takes place in the stroma of the chloroplast
• The product is triose phosphate using Carbon dioxide and ribulose bisphosphate (a 5-carbon compound)
• Triose phosphate is used in the production of glucose and other organic molecules
• The cycle requires both H+ ions and electrons

1) Formation of glycate 3-phosphate
• CO2 enters through the stomata of the leaf and diffuses into the stroma of the chloroplast
• In the stroma, the CO2 is combined with ribulose bisphosphate (RuBP)
• The enzyme rubisco catalyses the reaction
• The product is an unstable 6 carbon compound which quickly breaks down into 2 molecules of 3 carbon compounds called glycate 3-phosphate (GP)

RuBP + CO2 – Rubisco  unstable 6 carbon compound  2GP

2) Formation of triose phosphate
• Hydrolysing ATP provides the required energy to reduce glycate 3-phospate (GP) to a different 3-carbon compound, triose phosphate (TP)
• The reaction requires a H+ which comes from the reduced NADP
• Reduced NADP is recycled to form NADP
• Some of the triose phosphate is converted into useful organic compounds such as glucose whilst the rest of it continues in the Calvin cycle to regenerate RuBP

3) Regeneration of ribulose bisphosphate
• For every 6 molecules of TP produced, 5 of them are not used to make a useful organic compound but rather to regenerate the RuBP
• Regenerating RuBP requires all of the ATP produced via the light dependent reaction