The Light-Independent Stage

Question 0

Where does the Calvin cycle take place?

Answer 0

Stroma

Question 1

What does the Calvin cycle require in order to take place?

Answer 1

• Requires no light.
• Requires the products from the light-dependent stage.
• If no light is available the light-independent stage will not happen.

Question 2

Explain the Calvin Cycle (light-independent stage)

Answer 2

• CO2 diffuses through stomata into palisade cells and into the stroma.
• Rubisco catalyses the carboxylation of RUBP with CO2 to form the unstable 6C intermediate.
• The 6C intermediate is split into 2x3C Glycerate-3-phosphate (GP), fixing the CO2.
• The GP is reduced using reduced NADP from the light-dependent stage (reduced NADP is.oxidised back into NADP) and phosphorylated using ATP from the light-dependent stage (ATP is dephosphorylated) into ADP + Pi) –> this forms 2x3C Triose Phosphate (TP).
• 5/6 of the TP made is used to regenerate RUBP (5x3C TP {15C} –> 3x5C RUBP {15C})

• 1/6 of the TP is used to make Hexose Sugars (e.g. Glucose).
↪️ This can be changed into fructose, polymerised into starch and cellulose, and some TP is allowed to make glycerol.

• Some GP is used to make amino acids and fatty acids.

• Fatty acids + glycerol are used to make lipids
* EVERY STEP IS ENZYME CATALYSED

Question 3

What is the role of carbon dioxide in the Calvin cycle?

Answer 3

• carbon dioxide is the source of carbon and oxygen for the production of all large organic molecules