5.6.7 The Light-Independent Stage

Question 1

What is the light independent stage?

Answer 1

3- Calvin cycle
- Produces starch, sucrose and cellulose
- Takes place in darkness, doesn’t need light
- Needs NADP and ATP from light dependent stage

3 main steps
- Ribulose bisphosphate becomes carboxylated as it combines with CO2
- Catalysed by rubisco
- 6C intermediate forms, unstable
- So splits into 2 3C intermediates called glycerate-3-phosphate (GP)
- CO2 has now been fixated
- GP reduced to TP using hydrogens from reduced NADP using ATP
- 1/6 of TP used to create useful molecules for plant
- 5/6 of TP used to regenerate RUBP, requiring ATP
- Rubisco bisphosphate is regenerated from TP in reactions using ATP