1. Also known as the dark reaction
The Calvin Cycle
Also known as the dark reaction

2. The Dark Reaction
Calvin cycle – a cycle that uses ATP and NADPH, from the light reaction, to make glucose, without the use of light energy.

3. Carbon Fixation by the Calvin Cycle
From the light reaction, NADPH, ATP and oxygen was produced.
Carbon fixation: C is bonded, or fixed, into an organic compound
Calvin cycle has 3 major steps occurring in the stroma

4. Carbon dioxide diffuses into the stroma from the surrounding cytosol
Step One
Carbon dioxide diffuses into the stroma from the surrounding cytosol
An enzyme combines CO2 with RuBP, a 5 carbon molecule
The 6 carbon molecules splits into two 3-C molecules called PGA

6. Step Two PGA is converted into another 3-C molecule called PGAL
Each PGA gains a phosphate from a molecule of ATP
This compound receives a proton (H+) from NADPH, then releases the phosphate group.
The resulting NADP+, ADP and phosphate go back to the light reaction

8. So RuBP actually begins and ends the Calvin Cycle.
Step Three
Most of the PGAL is converted back to RuBP by using up a phosphate from ATP, making ADP
So RuBP actually begins and ends the Calvin Cycle.

10. Where’d that other Carbon go
Some PGAL and other molecules made in the Calvin cycle are used to make amino acids, lipids, and carbohydrates.
Carbohydrates include glucose, fructose, sucrose, glycogen, starch, and cellulose.

12. For 3 turns, 9 molecules of ATP and 6 molecules of NADPH are used.
How Many?
PGAL is a 3-C molecule, and one turn of the Calvin cycle fixes one carbon, so it takes 3 turns of the cycle to make 1 PGAL.
For 3 turns, 9 molecules of ATP and 6 molecules of NADPH are used.

13. Equations CO2 + H2O + light energy  (CH2O) + O2

14. light-independent reactions in stroma of chloroplast
light-dependent reactions at thylakoids of chloroplast
light
LIGHT-DEPENDENT REACTIONS
6O2
CO2 into leaf
O2 out
12H2O
ADP + Pi
ATP
NADP+
NADPH
PGA
CALVIN-BENSON CYCLE
PGAL
6CO2
6H2O
RuBP P
C6H12O6
(phosphorylated glucose)
end product (e.g. sucrose, starch, cellulose)
Fig. 6.17, p. 127

15. Rate of Photosynthesis
Rate is affected by the environment
As light intensity increases, the rate increases then levels off.
As temperature increases, the rate increases, hits a peak, then declines.
As CO2 levels increase, the rate increases then levels off

16. Conclusion and Dark Reaction Chart
Location – Stroma, fluid in the chloroplast surrounding the Thylakoid membranes
Function – produce carbohydrates, (glucose)
Reactants – Carbon Dioxide, RuBP, ATP and NADPH+
Products – Glucose, ADP and NADP-