Calvin cycle
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What are the products from the light INDEPENDANT reaction that are used in this reaction
Reduced NADP and ATP
Why is the light independent reaction not truly independant
It uses products from the light dependant reaction as reactants reaction so without light this cycle will run out
Where does the calvin cycle take place
In the stroma of chloroplasts
Fixation of carbon dioxide (First step)
Carbon dioxide combines with the 5-carbon chain called ribulose bisphosphate (RuBP) in a reaction catalysed by RuBisCo This results in an unstable intermediate which is quickly split into two 3 carbon chains molecules called glycerate 3-phosphate (GP)
Second step (Reduction of GP)
Both molecules of GP are reduced using energy from 2 ATP and 2 reduced NADP as the reducing agent. They are reduced into 2x 3 Triose phosphate
Third step (Regeneration of RuBP)
One carbon atom out of both of the two Triose Phosphate molecules is used for making useful organic substances (Glucose, Sucrose, Cellulose, Starch, glycerol etc) The other 5 carbon atoms are converted back into RuBP using energy from ATP
Exam tip
while the specification uses abbreviations for GP and RuBP, it does not use an abbreviation for triose phosphate, which is often abbreviated in textbooks and notes to TP; be sure to always write triose phosphate in full the first time you use the term in an exam 🌞
How many turns are needed to make a hexose sugar?
1 turn = 2 Triose Phosphate molecules 3 Turns = 6 triose phosphate molecules However only 1 carbon atom is used for useful organic substances each time and hexose has six carbons therefore: The calvin cycle must undergo 6 turns to make 6 carbons useful for organic substances In these 6 turns it requires 18 ATP molecules and 12 reduced NADP