light independent reaction

another name for the light independent reaction?

• the calvin cycle

what are the 3 main steps in the calvin cycle?

• carbon fixation

• reduction

• regeneration

carbon fixation?

• when carbon dioxide diffuses into the leaves through the stomata, it combines with RuBP to give an unstable 6 carbon compound

• this is catalysed by enzyme- rubisco

• the unstable 6 carbon molecule rapidly splits into 2 molecules of GP

  • the combination of CO2 with RuBP is described as carbon fixation

reduction?

• the 2 molecules of GP are then reduced to triose phosphate

• this reaction is driven by energy from 2 molecules of ATP and protons from 2 molecules of reduced NADP

• one out of every 6 triose phosphate molecules is converted into hexose sugars but most continue in the calvin cycle

regeneration?

• 5 out of every 6 triose phosphate molecules are not converted into sugars- these are used to regenerate RuBP

• this reaction is driven by one molecule of ATP which is then recycled in the light-dependent reaction

  • the formation of RuBP from triose phosphate allows the calvin cycle to continue

what suibstances are triose phosphate and GP converted into?

• carbohydrates

• lipids

• amino acids

carbohydrates?

• hexose sugars (glucose) are produced from 2 molecules of triose phosphate

• hexose sugars can be joined together to form larger carbohydrates, such as starch and cellulose

lipids?

• make from glycerol and fatty acid chains

• triose phosphate molecules are used in the synthesis of glycerol

• fatty acids are synthesised from GP

amino acids?

• GP is used in the synthesis of some amino acids

why does the calvin cycle need to turn 6 times to make glucose?

• three turns of the cycle produces 6 molecules of triose phosphate, because 2 molecules of triose phosphate are made for every one CO2 molecule used

• 5 out of every 6 of these triose phosphate molecules are used to regenerate RuBP

• this means that for 3 turns of the cycle, only 1 TP is produced that is used to make a hexose sugar

• a hexose sugar has 6 carbons though, so 2 triose phosphate molecules are needed to form one hexose sugar

• this measn the cycle must turn 6 times to produce 2 molecules of triose phosphate that can be used to make one hexose sugar

• 6 turns of the cycle need 18 ATP and 12 reduced NADP from the light dependent reaction

  • this may seem inefficient, but it keeps the cycle going and makes sure there is always enough RuBP ready to combine with CO2 taken in from the atmosphere