5.6.4 light-independent stage

Question 1

where does the light-independent stage happen

Answer 1

stroma of chloroplasts

Question 2

how is the calvin cycle dependent on the light-dependent stage of photosynthesis

Answer 2

ATP & hydrogen are required to reduce carbon dioxide & synthesise large complex organic molecules

Question 3

5 steps of the calvin cycle (light-independent stage of photosynthesis)

Answer 3

1. carbon dioxide combines with ribulose bisphosphate (RuBP)
   - catalysed by RuBisCO
2. RuBP becomes carboxylated forming unstable intermediate 6C compound which immediately breaks down
3. product is 2 molecules of 3C compound, GP (glycerate-3-phosphate)
   - carbon dioxide has been fixed
4. GP reduced, with 2 hydrogens from NADPH (light-dependent stage), to triose phosphate (TP)
   - energy from ATP (light-dependent stage) used at rate of 2 ATP for every carbon dioxide fixed in stage 3
5. in 10 of every 12 TP molecules, atoms rearranged to generate 6 molecules of RuBP
   - requires phosphate groups (from ATP)
   - chloroplasts contain low levels of RuBP as constantly converted to GP, but constantly regenerated
   - remaining 2 of 12 TP are product

Question 4

how many turns of calvin cycle is necessary to produce 2 molecules of TP to make one molecules of glucose

Answer 4

6

Question 5

why does calvin cycle only run in daylight

Answer 5

products (ATP & NADPH) from light-dependent stage constantly needed for calvin cycle

Question 6

uses of triose phosphate (TP)

Answer 6

1. some TP molecules synthesise organise compounds, eg:
   - some glucose converted to sucrose, starch & cellulose
   - some TP synthesises amino acids, fatty acids & glycerol
2. rest of TP recycled to regenerate RuBP