1. THE CALVIN CYCLE: REDUCING CO2TO SUGAR
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2. 7.10 The Calvin cycle generates sugar within chloroplast
CO2 ATP NADPH
Input
GOAL - Reduce CO2 to produce the 3-Carbon sugar G3P.
Reactants: CO2 enter from stomata, ATP and NADPH from light reactions
A plant cell may then use G3P to make glucose and other organic molecules.
Equation for Calvin Cycle:
3 CO2 + 9 ATP + 6 NADPH
G3P + 9 ADP + 6 NADP+ + P
Calvin Cycle
Student Misconceptions and Concerns
The terms light reactions and dark reactions can lead students to conclude that each set of reactions occurs at different times of the day. However, the Calvin cycle in most plants occurs during daylight, when NADPH and ATP from the light reactions are readily available.
Teaching Tips
Glucose is not the direct product of the Calvin cycle, as might be expected from the general equation for photosynthesis. Instead, as noted in the text, G3P is the main product. Clarify the diverse uses of G3P in the production of many important plant molecules for students.
Output:
G3P
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3. 7.10 The Calvin Cycle The steps of the Calvin cycle include
carbon fixation,
reduction,
release of G3P, and
regeneration of the starting molecule ribulose bisphosphate (RuBP).
Student Misconceptions and Concerns
The terms light reactions and dark reactions can lead students to conclude that each set of reactions occurs at different times of the day. However, the Calvin cycle in most plants occurs during daylight, when NADPH and ATP from the light reactions are readily available.
Teaching Tips
Glucose is not the direct product of the Calvin cycle, as might be expected from the general equation for photosynthesis. Instead, as noted in the text, G3P is the main product. Clarify the diverse uses of G3P in the production of many important plant molecules for students.
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4. Rubisco = enzyme responsible for Carbon fixation: RuBP + CO2 2 3-PGA
Input: 3
CO2
Step Carbon fixation 1
Rubisco 1 3 P P 6 P
RuBP
3-PGA
Calvin Cycle
Figure 7.10B_s1 Details of the Calvin cycle, which takes place in the stroma of a chloroplast (step 1)
Rubisco = enzyme responsible for Carbon fixation:
RuBP + CO PGA 4

5. Step Carbon fixation Input: 3 CO2 Rubisco 3 P P 6 P RuBP 3-PGA
Figure 7.10B_s2
Step Carbon fixation 1
Input: 3
CO2
Rubisco 1 3 P P 6 P
RuBP
3-PGA
Step Reduction 2 6
ATP 6
ADP P
Calvin Cycle 2 6
NADPH 6
NADP
Figure 7.10B_s2 Details of the Calvin cycle, which takes place in the stroma of a chloroplast (step 2) 6 P
G3P 5

6. Step Release of one molecule of G3P 6 NADP 6 P 5 P G3P G3P
Figure 7.10B_s3
Step Carbon fixation 1
Input: 3
CO2
Rubisco 1 3 P P 6 P
RuBP
3-PGA
Step Reduction 2 6
ATP 6
ADP P
Calvin Cycle 2 6
NADPH
Step Release of one molecule of G3P 3 6
NADP
Figure 7.10B_s3 Details of the Calvin cycle, which takes place in the stroma of a chloroplast (step 3) 6 P 5 P
G3P
G3P 3
Glucose and other compounds
Output: 1 P
G3P 6

7. Step Release of one molecule of G3P 6 NADP 6 P 5 P G3P G3P
Figure 7.10B_s4
Step Carbon fixation 1
Input: 3
CO2
Rubisco 1 3 P P 6 P
RuBP
3-PGA
Step Reduction 2 6
ATP 3
ADP 6
ADP P
Calvin Cycle 4 2 3
ATP 6
NADPH
Step Release of one molecule of G3P 3 6
NADP
Figure 7.10B_s4 Details of the Calvin cycle, which takes place in the stroma of a chloroplast (step 4) 6 P 5 P
G3P
G3P 3
Glucose and other compounds
Step Regeneration of RuBP 4
Output: 1 P
G3P 7

8. Calvin Cycle (in stroma)
The Fate of G3P
50% of carbs made by photosynthesis are used as fuel for plants
Cellular respiration in the mitochondria!!!
G3P serves as starting material for making other organic molecules:
proteins, lipids, and cellulose.
Excess carbs stored as starch in roots, stems, etc.
CO2
RuBP
Calvin Cycle (in stroma)
3-PGA
Stroma
G3P
Cellular respiration
Figure 7.12 A summary of photosynthesis
Cellulose
Starch
Sugars
Other organic compounds 8

9. Photosynthesis and Cellular Respiration Form a Cycle!!
sun
ATP produced by light reactions is ONLY used by Calvin cycle - never leaves chloroplast!
Photosynthesis
(chloroplasts)
photoautotrophs
glucose sugar
CO2 +
H2O + O2
Respiration
(mitochondria)
Student Misconceptions and Concerns
Some students do not realize that plant cells also have mitochondria. Instead, they assume that the chloroplasts are sufficient for the plant cell’s needs. As noted in the text, nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria).
Teaching Tips
1. Challenge students to explain how the energy in beef is ultimately derived from the sun.
2. The authors note that G3P is also used to produce cellulose, the most abundant organic molecule in a plant and probably on the surface of the Earth!
Heterotrophs and autotrophs
ATP
USED FOR CELLULAR WORK!!
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10. Factors Affecting the Rate of Photosynthesis

11. Photorespiration decreases energy yields in plants!!
Photorespiration = Reduced energy yields due to high O2 levels!!
Under water stress or dehydration,
Stomata close due to decreased turgor pressure of guard cells
Gas exchange reduced -- O2 levels increase, CO2 levels decrease
Rubisco adds O2 to RuBP instead of CO2
This process is called photorespiration because it occurs in the light, consumes O2, releases CO2, wastes ATP resources!!!
Teaching Tips
1. If you can find examples of C3, C4, and CAM plants, consider bringing them to class. Referring to living plants helps students understand these abstract concepts. Nice photographs can serve as a substitute.
2. Relate the properties of C3 and C4 plants to the regions of the country where each is grown. Students might generally understand that crops have specific requirements, but may not specifically relate these physiological differences to their geographic sites of production or specific evolutionary histories.
Photorespiration decreases energy yields in plants!!
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12. Typical Plants are C3 Plants - Fix CO2 by Rubisco forming 3-PGA
C3 plants are more affected by Photorespiration!

13. Fig. 6.15a

14. Alternative methods of Carbon Fixation to Prevent Photorespiration
C4 plants have evolved a means of
Limiting water loss while optimizing the Calvin cycle.
C4 plants first fix CO2 into a four-carbon compound.
Mesophyll cell
CO2
4-C compound
Bundle- sheath cell
CO2
Calvin Cycle
Teaching Tips
1. If you can find examples of C3, C4, and CAM plants, consider bringing them to class. Referring to living plants helps students understand these abstract concepts. Nice photographs can serve as a substitute.
2. Relate the properties of C3 and C4 plants to the regions of the country where each is grown. Students might generally understand that crops have specific requirements, but may not specifically relate these physiological differences to their geographic sites of production or specific evolutionary histories.
3-C sugar
C4 plant
Sugarcane
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15. Fig. 6.15a

16. Adaptations to Prevent Photorespiration, cont’d
CAM plants conserve water by opening their stomata and admitting CO2 only at night.
CO2 is fixed into a four-carbon compound,
which banks CO2 at night and
releases it to the Calvin cycle during the day.
CO2
Night
4-C compound
CO2
Calvin Cycle
Teaching Tips
1. If you can find examples of C3, C4, and CAM plants, consider bringing them to class. Referring to living plants helps students understand these abstract concepts. Nice photographs can serve as a substitute.
2. Relate the properties of C3 and C4 plants to the regions of the country where each is grown. Students might generally understand that crops have specific requirements, but may not specifically relate these physiological differences to their geographic sites of production or specific evolutionary histories.
3-C sugar
Day
CAM plant
Pineapple
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17. You should now be able to
Define autotrophs, heterotrophs, producers, and photoautotrophs.
Describe the structure of chloroplasts and their location in a leaf.
Explain how plants produce oxygen.
Describe the role of redox reactions in photosynthesis and cellular respiration.
Compare the reactants and products of the light reactions and the Calvin cycle.
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18. You should now be able to
Describe the properties and functions of the different photosynthetic pigments.
Explain how photosystems capture solar energy.
Explain how the electron transport chain and chemiosmosis generate ATP, NADPH, and oxygen in the light reactions.
Compare photophosphorylation and oxidative phosphorylation.
Describe the reactants and products of the Calvin cycle.
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19. You should now be able to
Compare the mechanisms that C3, C4, and CAM plants use to obtain and use carbon dioxide.
Review the overall process of the light reactions and the Calvin cycle, noting the products, reactants, and locations of every major step.
Describe the greenhouse effect.
Explain how the ozone layer forms, how human activities have damaged it, and the consequences of the destruction of the ozone layer.
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