Light Independent Photosynthesis

Question 1

What is the light independent reaction for?

Answer 1

Occurs when there is no light, and uses products of cyclic photophosphorylation (reduced NADP, ATP) and carbon dioxide to make glucose.
Process depends on the supply of the products and won’t occur if there isn’t enough.
This is done through the CALVIN CYCLE.

Question 2

Where does the reaction occur?

Answer 2

Stroma of chloroplast.

Question 3

What happens in carbon fixation?

Answer 3

Carbon dioxide combines with ribulose biphosphate (RuBP) using RUBISCO(carboxylated)
This forms an unstable 6C compound intermediate which breaks down to form 2 molecules of GLYCERATE-3-PHOSPHATE (GP)
6C is unstable so its excess energy causes it to split and carbon is fixed.

Question 4

What happens in reduction?

Answer 4

GP is reduced to form 2 molecules of GLYCERALDEHYDE PHOSPHATE (GALP) using reduced NADP (gives H ions) and ATP. .

GALP can be used as a raw material in the production of amino acids, monosaccharides and other molecules.

Question 5

What happens in regeneration?

Answer 5

RuBP needs to be regenerated to continue the Calvin cycle, using ATP.

Question 6

What are the products of both reactions?

Answer 6

LDR - half an oxygen molecule, ATP and reduced NADP
LIR - two GALP molecules, oxidised NADP and ADP (reduced to be used again in the LDR)