1. Calvin Cycle Also know as Calvin – Benson Cycle
Light Independent Reactions
(Dark Reactions – not a good term as it implies this only occurs at night)

2. ELECTRON TRANSPORT CHAIN
The production of ATP AND NADPH the light reaction of photosynthesis
Thylakoid compartment (high H+)
Light
Light
Thylakoid membrane
Antenna molecules
Stroma (low H+)
ELECTRON TRANSPORT CHAIN
PHOTOSYSTEM II
PHOTOSYSTEM I
ATP SYNTHASE
Figure 7.9

3. ATP and NADPH power sugar synthesis in the Calvin cycle
The Calvin cycle occurs in the chloroplast’s stroma
This is where carbon fixation takes place and sugar is manufactured
INPUT
CALVIN CYCLE
Figure 7.10A
OUTPUT:

4. Details of the Calvin cycle
INPUT: 3
In a reaction catalyzed by rubisco, 3 molecules of CO2 are fixed.
CO2
Step Carbon fixation. 1 1 3 P P 6 P
RuBP
3-PGA 6
ATP
3 ADP
Step Energy consumption 2
6 ADP + P 3
ATP
CALVIN CYCLE 2 6 4
NADPH
6 NADP+
Step Release of one molecule of G3P. 3 5 P 6 P
G3P
G3P 3
Step Regeneration of RuBP. 4
Glucose and other compounds
OUTPUT: 1 P
G3P
Figure 7.10B

5. Step 1 Carbon Fixation
CO2 is incorporated (fixed) into a five-carbon sugar named ribulose bisphosphate (RuBP).
The enzyme that does this is RuBP carboxylase or rubisco.
The most abundant protein on Earth.

6. Step 2 Energy consumption
ATP and NADPH2 (from the light reaction) are used to make the three-carbon precursor that will be used to make glucose and other sugars.

7. Step 3 Glucose
For every three molecules of CO2 that enter the cycle, the net output is one molecule of glyceraldehyde 3-phosphate (G3P)
Used to make Glucose

8. Step 4 Regeneration of RuBP
ATP is used to regenerate RuBP from G3P

9. Energy cost of Calvin Cycle
For each G3P synthesized, the cycle spends:
9 ATP
6 NADPH2.
Both are made in the light reaction

10. http://highered. mcgraw-hill

11. Review: Photosynthesis uses light energy to make food molecules
A summary of the chemical processes of photo-synthesis
Chloroplast
Light
Photosystem II Electron transport chains Photosystem I
CALVIN CYCLE
Stroma
Electrons
Cellular respiration
Cellulose
Starch
Other organic compounds
LIGHT REACTIONS
CALVIN CYCLE
Figure 7.11

12. Many plants make more sugar than they need
The excess is stored in roots, tubers, and fruits
These are a major source of food for heterotrophs

13. C4 and CAM plants have special adaptations that save water
Most plants are C3 plants, which take CO2 directly from the air and use it in the Calvin cycle
In these types of plants, stomata on the leaf surface close when the weather is hot
This causes a drop in CO2 and an increase in O2 in the leaf
Photorespiration may then occur
No sugar or ATP

14. Photorespiration in a C3 plant
CALVIN CYCLE
2-C compound
Figure 7.12A

15. Some plants have special adaptations that enable them to save water
Special cells in C4 plants—corn and sugarcane—incorporate CO2 into a four-carbon molecule
This molecule can then donate CO2 to the Calvin cycle
4-C compound
CALVIN CYCLE
3-C sugar
Figure 7.12B

16. The CAM plants—pineapples, most cacti, and succulents—employ a different mechanism
They open their stomata at night and make a four-carbon compound
It is used as a CO2 source by the same cell during the day
4-C compound
Night
Day
CALVIN CYCLE
3-C sugar
Figure 7.12C

17. PHOTOSYNTHESIS, SOLAR RADIATION, AND EARTH’S ATMOSPHERE
Due to the increased burning of fossil fuels, atmospheric CO2 is increasing
CO2 warms Earth’s surface by trapping heat in the atmosphere
This is called the greenhouse effect

18. Sunlight
ATMOSPHERE
Radiant heat trapped by CO2 and other gases
Figure 7.13A & B

19. Because photosynthesis removes CO2 from the atmosphere, it moderates the greenhouse effect
Unfortunately, deforestation may cause a decline in global photosynthesis

20. Mario Molino received a Nobel Prize in 1995 for his work on the ozone layer
His research focuses on how certain pollutants (greenhouse gases) damage that layer
Figure 7.14A

21. Sunlight
ATMOSPHERE
Radiant heat trapped by CO2 and other gases
Figure 7.13A & B

22. Because photosynthesis removes CO2 from the atmosphere, it moderates the greenhouse effect
Unfortunately, deforestation may cause a decline in global photosynthesis

23. 7.14 Talking About Science: Mario Molina talks about Earth’s protective ozone layer
Mario Molino received a Nobel Prize in 1995 for his work on the ozone layer
His research focuses on how certain pollutants (greenhouse gases) damage that layer
Figure 7.14A

24. The O2 in the atmosphere results from photosynthesis
Solar radiation converts O2 high in the atmosphere to ozone (O3)
Ozone shields organisms on the Earth’s surface from the damaging effects of UV radiation

25. Industrial chemicals called CFCs have hastened ozone breakdown, causing dangerous thinning of the ozone layer
International restrictions on these chemicals are allowing recovery
Sunlight
Southern tip of South America
Antarctica
Figure 7.14B