Light Independent Reaction - Calvin Cycle

Question 1

What are the stages of the light independent reaction? (Calvin cycle)

Answer 1

The Calvin cycle occurs in the STROMA
* This is where carbon is “fixed”/incorporated into organic molecules using COz as the raw material
* CO2 diffuses into the leaf via the stomata, across the spaces of the spongy mesophyll, into the mesophyll cells, then into the chloroplast stroma
: The co lapsed eternepto freule alad pup filose bishosphate)
* An unstable 6C molecule is formed
* This immediately splits into 2 X GP (Glycerate-3-phosphate)
* Then, the useful products from the light dependent stage are needed for the next
step
* The GP is converted into 2 X TP (triose phosphate)
The reduced NADP acts as a “reducing agent” & donates hydrogen atoms
The ATP acts as an energy source
* TP is a 3C sugar (the whole point of PHS is to make sugars!!)
* 5/6 of the TP has to be used to regenerate the RUBP, to keep the cycle going
* 1/6 of the TP can be used to make other carbohydrates e.g. glucose, sucrose (disacc), starch & cellulose (polysacc’s)
* TP is also used to make glycerol, fatty acids and amino acids - lots of crucial substances for the plant.

Question 2

What are the 3 main stages of the Calvin cycle?

Answer 2

Fixation - carbon dioxide is fixed (incorporated into an organic molecule) in the first step.
* Reduction - GP is reduced to TP by the addition of hydrogen from reduced NADP using energy supplied by ATP.
* Regeneration - RuBP is regenerated from the recycled TP.