light independent reaction (Calvin cycle)

where does light independent reaction take place?

stroma

stages of calvin cycle

-carbon fixation

-reduction of glycerate 3-phosphate

-regeneration of ribulose bisphosphate

carbon fixation

-Carbon dioxide combines with ribulose bisphosphate (RuBP)

-this forms an unstable 6 carbon compounds which splits into two glycerate 3-phosphate (GP)

-this is catalysed by the enzyme ribulose bisphosphate carboxylase (RuBisCO)

reduction of glycerate 3-phosphate

-GP is reduced into triose phosphate

-ATP provides energy

-Reduced NADP provides hydrogen

-this regenerates NADP (used in the light-dependent reaction again)

regeneration of ribulose bisphosphate

-most TP is used to regenerate RuBP and the rest of the TP is used to produce organic compounds

→five out of every six TP molecules produced are used to regenerate RuBP. This regeneration requires ATP

How many full turns of the Calvin Cycle are required to produce one glucose molecule (hexose sugar)?

6

Why does the Calvin cycle require six turns to create a single hexose sugar?

Each turn of the Calvin cycle fixes one CO₂ molecule

One TP molecule contains 3 carbon atoms

A hexose sugar contains 6 carbon atoms so two TP molecules are required to form one hexose sugar

The cycle requires 6 turns to produce 2 TP that can be used to make one glucose molecule.

how many TP molecules are produced in 6 turns of the Calvin cycle?

How many are removed to produce glucose?

How many are used to regenerate RuBP?

-12 (Each turn produces 2 TP→6 turns × 2 TP per turn = 12 TP)

-2 [2 out of every 12 TP molecules]

-10 [10 out of every 12 TP molecules are used]

TP is used to make (4):

-carbohydrates

-lipids

-amino acids

-regenerate RuBP

examples of carbohydrates made

-sucrose, starch and cellulose→ made by joining hexose sugars together

[larger carbohydrates]

role of ATP in Calvin cycle (2)

-provides energy to reduce GP into TP

-provides energy for the regeneration of RuBP

how many ATP are needed to make one hexose sugar?

how many reduced NADP are needed to make one hexose sugar?

-18

-12

does Calvin cycle require light energy?

it does not directly require light energy.

what happens when its dark? (4)

-The Calvin cycle does not directly require light, but it cannot run for long in the dark.

-light dependent reaction stops so no ATP and reduced NADP are produced

-this means GP cannot be reduced to TP and RuBP cannot be regenerated

-the Calvin cycle stops as it depends on ATP and reduced NADP