light-independent stage

Cards (11)

  • Phase 1
    • CO2 enters leaf through stomata and diffuses into stroma of chloroplasts
    • combines with RuBP, a 5 carbon compound
    • this unstable 6-carbon compound quickly breaks down into 2 molecules of a 3-carbon compound called glycerate 3-phosphate
    • the enzyme RuBisCO catalyses the reaction between the two
  • phase 2
    • ATP from light-dependent reaction provides energy to turn the 3-carbon GP into a different 3-carbon compound called triose phosphate (TP)
    • reaction requires H+ ions which come from reduced NADP. Reduced NADP is recycled to NADP
    • TP converted into many useful organic compounds such as glucose
  • phase 3
    • 5 out of every 6 molecules of TP used to regenerate RuBP
    • regenerating RuBP takes rest of the ATP produced by light-dependent reaction
  • calvin cycle
    • RuBP = 5 carbons
    • GP = 3 carbons
    • triose phosphate (TP) = 3 carbons
    • Hexose = 6 carbons
  • where in the chloroplast does the light-independent reaction take place?

    stroma
  • why the amount of GP increases after a photosynthesising plant has been in darkness for a short time 

    • GP cannot be converted to triose phosphate since this requires ATP/ reduced NADP
  • describe the role of water in the light-dependent reaction of photosynthesis
    • provides protons (H+ ions) for reduction of NADP
  • turns in calvin cycle to make hexose
    • calvin cycle needs 6 turns to make one hexose sugar
    • 3 turns of cycle makes 6 molecules of TP - 2 molecules of TP are mae for every one CO2 used
    • 5 out of 6 of these TP molecules use to regenerate RuBP
    • for 3 turns, only one TP produced thats used to make hexose sugar
    • hexose has 6 carbons, 2 TP molecules are needed to make 1 hexose
    • cycle must turn 6 times to produce 2 TP molecules to make 1 hexose
    • 6 turns of cycle need 18 ATP and 12 Reduced NADP from light dependent reaction
  • calvin cycle steps
    1. CO2 combines with CO2 acceptor, a 5 carbon compound called ribulose biphosphate (RuBP). this is catalysed by enzyme RuBisCO
    2. RuBP by accepting carboxyl group becomes carboxylated, forming unstable 6 carbon compound
    3. product of reaction is 2 molecules of 3 carbon compound GP. CO2 now fixed
    4. GP reduced, using hydrogens from reduced NADP, to TP.
  • calvin cycle only runs during the day