1. There are two types of photosystems in the thylakoid membrane
Photosystem II (PS II) functions first (the numbers reflect order of discovery) and is best at absorbing a wavelength of 680 nm
The reaction-center chlorophyll a of PS II is called P680
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2. Photosystem I (PS I) is best at absorbing a wavelength of 700 nm
The reaction-center chlorophyll a of PS I is called P700
P680 and P700 are nearly identical, but their association with different proteins results in different light-absorbing properties
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3. Linear Electron Flow
Linear electron flow involves the flow of electrons through the photosystems and other molecules embedded in the thylakoid membrane to produce ATP and NADPH using light energy
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4. Linear electron flow can be broken down into a series of steps
A photon hits a pigment and its energy is passed among pigment molecules until it excites P680
An excited electron from P680 is transferred to the primary electron acceptor (we now call it P680+)
H2O is split by enzymes, and the electrons are transferred from the hydrogen atoms to P680+, thus reducing it to P680; O2 is released as a by-product
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5. Each electron “falls” down an electron transport chain from the primary electron acceptor of PS II to PS I
Energy released by the fall drives the creation of a proton gradient across the thylakoid membrane; diffusion of H+ (protons) across the membrane drives ATP synthesis
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6. In PS I (like PS II), transferred light energy excites P700, causing it to lose an electron to an electron acceptor (we now call it P700+)
P700+ accepts an electron passed down from PS II via the electron transport chain
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7. Excited electrons “fall” down an electron transport chain from the primary electron acceptor of PS I to the protein ferredoxin (Fd)
The electrons are transferred to NADP+, reducing it to NADPH, and become available for the reactions of the Calvin cycle
This process also removes an H+ from the stroma
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8. LIGHT REACTIONS CALVIN CYCLE
Figure 8.UN02
H2O
CO2
Light
NADP+
ADP
LIGHT
REACTIONS
CALVIN
CYCLE
ATP
NADPH
Figure 8.UN02 In-text figure, light reaction schematic, p. 170 O2
[CH2O] (sugar)
© 2017 Pearson Education, Ltd.

9. P680 Light Pigment molecules Photosystem II (PS II) Primary acceptor
Figure 8.13-s1
Primary
acceptor e-
P680
Light
Figure 8.13-s1 How linear electron flow during the light reactions generates ATP and NADPH (step 1)
Pigment
molecules
Photosystem II
(PS II)
© 2017 Pearson Education, Ltd.

10. 2 H+ + P680 Light Pigment molecules Photosystem II (PS II) /2 Primary
Figure 8.13-s2
Primary
acceptor
2 H+
H2 O e- + 1 /2 O2 e- e-
P680
Light
Figure 8.13-s2 How linear electron flow during the light reactions generates ATP and NADPH (step 2)
Pigment
molecules
Photosystem II
(PS II)
© 2017 Pearson Education, Ltd.

11. Electron transport chain 2 H+ + P680 Light Pigment molecules
Figure 8.13-s3
Electron
transport
chain
Primary
acceptor Pq
2 H+
H2 O e- +
Cytochrome
complex 1 /2 O2 Pc e- e-
P680
Light
ATP
Figure 8.13-s3 How linear electron flow during the light reactions generates ATP and NADPH (step 3)
Pigment
molecules
Photosystem II
(PS II)
© 2017 Pearson Education, Ltd.

12. Photosystem I (PS I) Photosystem II (PS II)
Figure 8.13-s4
Electron
transport
chain
Primary
acceptor
Primary
acceptor Pq e-
2 H+
H2 O e- +
Cytochrome
complex 1 /2 O2 Pc e-
P700 e-
P680
Light
Light
ATP
Figure 8.13-s4 How linear electron flow during the light reactions generates ATP and NADPH (step 4)
Pigment
molecules
Photosystem I
(PS I)
Photosystem II
(PS II)
© 2017 Pearson Education, Ltd.

13. Photosystem I (PS I) Photosystem II (PS II)
Figure 8.13-s5
Electron
transport
chain
Electron
transport
chain
Primary
acceptor
Primary
acceptor Fd
NADP+ Pq e-
2 H+ e-
+ H+
H2 O e- e- +
Cytochrome
complex
NADP+
reductase 1 /2 O2
NADPH Pc e-
P700 e-
P680
Light
Light
ATP
Figure 8.13-s5 How linear electron flow during the light reactions generates ATP and NADPH (step 5)
Pigment
molecules
Photosystem I
(PS I)
Photosystem II
(PS II)
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14. The energy changes of electrons during linear flow can be represented in a mechanical analogy
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15. Mill makes ATP NADPH ATP Photosystem II Photosystem I e- e- e- e- e-
Figure 8.14 e- e- e-
Mill
makes
ATP
NADPH e- e- e-
Photon
Figure 8.14 A mechanical analogy for linear electron flow during the light reactions e-
ATP
Photon
Photosystem II
Photosystem I
© 2017 Pearson Education, Ltd.

16. A Comparison of Chemiosmosis in Chloroplasts and Mitochondria
Chloroplasts and mitochondria generate ATP by chemiosmosis but use different sources of energy
Mitochondria transfer chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP
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17. Spatial organization of chemiosmosis differs between chloroplasts and mitochondria but there are also similarities
Both use the energy generated by an electron transport chain to pump protons (H+) across a membrane against their concentration gradient
Both rely on the diffusion of protons through ATP synthase to drive the synthesis of ATP
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18. In mitochondria, protons are pumped to the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix
In chloroplasts, protons are pumped into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma
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19. Electron transport chain
Figure 8.15
Mitochondrion
Chloroplast
Inter-
membrane
space H+
Diffusion
Thylakoid
space
Electron
transport
chain
Inner
membrane
Thylakoid
membrane
MITOCHONDRION
STRUCTURE
CHLOROPLAST
STRUCTURE
Figure 8.15 Comparison of chemiosmosis in mitochondria and chloroplasts
ATP
synthase
Matrix
Stroma
ADP + P i
ATP
Higher [H+] H+
Lower [H+]
© 2017 Pearson Education, Ltd.

20. Electron transport chain
Figure
MITOCHONDRION
STRUCTURE
CHLOROPLAST
STRUCTURE
Inter-
membrane
space H+
Diffusion
Thylakoid
space
Electron
transport
chain
Inner
membrane
Thylakoid
membrane
ATP
synthase
Figure Comparison of chemiosmosis in mitochondria and chloroplasts (part 1: detail)
Matrix
Stroma
ADP + P i
ATP
Higher [H+] H+
Lower [H+]
© 2017 Pearson Education, Ltd.

21. The light reactions of photosynthesis generate ATP and increase the potential energy of electrons by moving them from H2O to NADPH
ATP and NADPH are produced on the side of the thylakoid membrane facing the stroma, where the Calvin cycle takes place
The Calvin cycle uses ATP and NADPH to power the synthesis of sugar from CO2
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22. LIGHT REACTIONS CALVIN CYCLE
Figure 8.UN02
H2O
CO2
Light
NADP+
ADP
LIGHT
REACTIONS
CALVIN
CYCLE
ATP
NADPH
Figure 8.UN02 In-text figure, light reaction schematic, p. 170 O2
[CH2O] (sugar)
© 2017 Pearson Education, Ltd.

23. ½ Cytochrome complex NADP+ reductase Photosystem II Photosystem I
Figure 8.16
Cytochrome
complex
NADP+
reductase
Photosystem II
Photosystem I
Light
4 H+
Light
NADP+ + H+ Fd Pq
NADPH e- Pc e-
H2O O2
THYLAKOID SPACE
(high H+ concentration)
+2 H+
4 H+ To
Calvin
Cycle
Figure 8.16 The light reactions and chemiosmosis: the current model of the organization of the thylakoid membrane
Thylakoid
membrane
ATP
synthase
STROMA
(low H+ concentration)
ADP +
ATP P H+ i
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24. (high H+ concentration) 4 H+ +2 H+
Figure
Cytochrome
complex
Photosystem II
Photosystem I
Light
4 H+
Light Fd Pq Pc e- e-
H2O O2
THYLAKOID SPACE
(high H+ concentration)
4 H+
+2 H+
Figure The light reactions and chemiosmosis: the current model of the organization of the thylakoid membrane (part 1)
Thylakoid
membrane
ATP
synthase
STROMA
(low H+ concentration)
ADP +
ATP H+ P i
© 2017 Pearson Education, Ltd.

25. (high H+ concentration) 4 H+
Figure
Cytochrome
complex
NADP+
reductase
Photosystem I
Light
NADP+ + H+ Fd
NADPH Pc
THYLAKOID SPACE
(high H+ concentration)
4 H+ To
Calvin
Cycle
Figure The light reactions and chemiosmosis: the current model of the organization of the thylakoid membrane (part 2)
ATP
synthase
ADP
STROMA
(low H+ concentration) +
ATP H+
P i
© 2017 Pearson Education, Ltd.

26. Concept 8.3: The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar
The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules enter and leave the cycle
Unlike the citric acid cycle, the Calvin cycle is anabolic
It builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH
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27. The Calvin cycle has three phases
Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde 3-phospate (G3P)
For net synthesis of one G3P, the cycle must take place three times, fixing three molecules of CO2
The Calvin cycle has three phases
Carbon fixation
Reduction
Regeneration of the CO2 acceptor
© 2017 Pearson Education, Ltd. 27

28. CALVIN CYCLE LIGHT REACTIONS
Figure 8.UN03
H2O
CO2
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
Figure 8.UN03 In-text figure, Calvin cycle schematic, p. 174
NADPH O2
[CH2O] (sugar)
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29. The product is 3-phosphoglycerate
Phase 1, carbon fixation, involves the incorporation of the CO2 molecules into ribulose bisphosphate (RuBP) using the enzyme rubisco
The product is 3-phosphoglycerate
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30. 3 CO2, entering one per cycle
Figure 8.17-s1
Input:
3 CO2, entering one per cycle
Phase 1: Carbon fixation
Rubisco 3 P P 3 P P 6 P
RuBP
3-Phosphoglycerate
Calvin
Cycle
Figure 8.17-s1 The Calvin cycle (step 1)
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31. Phase 2, reduction, involves the reduction and phosphorylation of 3-phosphoglycerate to G3P
Six ATP and six NADPH are required to produce six molecules of G3P, but only one exits the cycle for use by the cell
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32. 3 CO2, entering one per cycle
Figure 8.17-s2
Input:
3 CO2, entering one per cycle
Phase 1: Carbon fixation
Rubisco 3 P P 3 P P 6 P
RuBP
3-Phosphoglycerate 6
ATP
6 ADP
Calvin
Cycle
6 P P
1,3-Bisphosphoglycerate
6 NADPH
6 NADP+ 6 P
Figure 8.17-s2 The Calvin cycle (step 2) i 6 P
G3P
Phase 2:
Reduction
Glucose and
other organic
compounds
Output: 1 P
G3P
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33. Three additional ATP are required to power this step
Phase 3, regeneration, involves the rearrangement of the five remaining molecules of G3P to regenerate the initial CO2 receptor, RuBP
Three additional ATP are required to power this step
© 2017 Pearson Education, Ltd. 33

34. 3 CO2, entering one per cycle
Figure 8.17-s3
Input:
3 CO2, entering one per cycle
Phase 1: Carbon fixation
Rubisco 3 P P 3 P P 6 P
RuBP
3-Phosphoglycerate 6
ATP
6 ADP
3 ADP
Calvin
Cycle
6 P P 3
ATP
1,3-Bisphosphoglycerate
6 NADPH
Phase 3:
Regeneration
of RuBP
6 NADP+ 6 P
Figure 8.17-s3 The Calvin cycle (step 3) i 5 P
G3P 6 P
G3P
Phase 2:
Reduction
Glucose and
other organic
compounds
Output: 1 P
G3P
© 2017 Pearson Education, Ltd.

35. Evolution of Alternative Mechanisms of Carbon Fixation in Hot, Arid Climates
Adaptation to dehydration is a problem for land plants, sometimes requiring trade-offs with other metabolic processes, especially photosynthesis
On hot, dry days, plants close stomata, which conserves H2O but also limits photosynthesis
The closing of stomata reduces access to CO2 and causes O2 to build up
These conditions favor an apparently wasteful process called photorespiration
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36. In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a three-carbon compound (3-phosphoglycerate)
In photorespiration, rubisco adds O2 instead of CO2 in the Calvin cycle, producing a two-carbon compound
Photorespiration decreases photosynthetic output by consuming ATP, O2, and organic fuel and releasing CO2 without producing any ATP or sugar
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37. Photorespiration may be an evolutionary relic because rubisco first evolved at a time when the atmosphere had far less O2 and more CO2
Photorespiration limits damaging products of light reactions that build up in the absence of the Calvin cycle
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38. C4 Plants
C4 plants minimize the cost of photorespiration by incorporating CO2 into a four-carbon compound
An enzyme in the mesophyll cells has a high affinity for CO2 and can fix carbon even when CO2 concentrations are low
These four-carbon compounds are exported to bundle-sheath cells, where they release CO2 that is then used in the Calvin cycle
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39. Sugarcane CO2 C4 Mesophyll Organic cell acid CO2 Bundle- sheath cell
Figure 8.18a
Sugarcane
CO2 C4
Mesophyll
cell
Organic
acid
CO2
Figure 8.18a C4 and CAM photosynthesis compared
Bundle-
sheath
cell
Calvin
Cycle
Sugar
(a) Spatial separation of steps
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40. Figure
Figure C4 and CAM photosynthesis compared (part 1: C4, sugarcane)
Sugarcane
© 2017 Pearson Education, Ltd.

41. CAM Plants
Some plants, including pineapples and many cacti and succulents, use crassulacean acid metabolism (CAM) to fix carbon
CAM plants open their stomata at night, incorporating CO2 into organic acids
Stomata close during the day, and CO2 is released from organic acids and used in the Calvin cycle
© 2017 Pearson Education, Ltd. 41

42. Pineapple CO2 CAM Organic acid Night CO2 Day Calvin Cycle Sugar
Figure 8.18b
Pineapple
CO2
CAM
Organic
acid
Night
CO2
Figure 8.18b C4 and CAM photosynthesis compared
Day
Calvin
Cycle
Sugar
(b) Temporal separation of steps
© 2017 Pearson Education, Ltd.

43. Figure
Figure C4 and CAM photosynthesis compared (part 2: CAM, pineapple)
Pineapple
© 2017 Pearson Education, Ltd.

44. The C4 and CAM pathways are similar in that they both incorporate carbon dioxide into organic intermediates before entering the Calvin cycle
In C4 plants, carbon fixation and the Calvin cycle occur in different cells
In CAM plants, these processes occur in the same cells, but at different times of the day
© 2017 Pearson Education, Ltd. 44

45. Calvin Cycle Calvin Cycle
Figure 8.18
Sugarcane
Pineapple
CO2
CO2 C4
CAM
Mesophyll
cell
Organic
acid
Organic
acid
Night
CO2
CO2
Figure 8.18 C4 and CAM photosynthesis compared
Bundle-
sheath
cell
Day
Calvin
Cycle
Calvin
Cycle
Sugar
Sugar
(a) Spatial separation of steps
(b) Temporal separation of steps
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46. The Importance of Photosynthesis: A Review
The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compounds
Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells
Plants store excess sugar as starch in the chloroplasts and in structures such as roots, tubers, seeds, and fruits
In addition to food production, photosynthesis produces the O2 in our atmosphere
© 2017 Pearson Education, Ltd. 46

47. Electron transport chain
Figure 8.19 O2
CO2
Mesophyll
cell
Sucrose
(export)
Chloroplast
H2O
H2O
CO2
Light
NADP+
ADP
3-Phosphoglycerate
LIGHT
REACTIONS:
Photosystem II
Electron transport chain
Photosystem I +
P i
CALVIN
CYCLE
RuBP
ATP
G3P
NADPH
Starch
(storage)
Figure 8.19 A review of photosynthesis O2
Sucrose (export)
LIGHT REACTIONS
CALVIN CYCLE REACTIONS
Are carried out by molecules in the thylakoid membranes
Convert light energy to the chemical energy of ATP and NADPH
Split H2O and release O2
Take place in the stroma
Use ATP and NADPH to convert CO2 to the sugar G3P
Return ADP, inorganic phosphate, and NADP+ to the light reactions
H2O
© 2017 Pearson Education, Ltd.

48. Electron transport chain
Figure
H2O
CO2
Light
NADP+
ADP
3-Phosphoglycerate
LIGHT
REACTIONS:
Photosystem II
Electron transport chain
Photosystem I +
P i
CALVIN
CYCLE
RuBP
ATP
G3P
Figure A review of photosynthesis (part 1: chloroplast)
Starch
(storage)
NADPH O2
Sucrose (export)
© 2017 Pearson Education, Ltd.

49. CALVIN CYCLE REACTIONS
Figure
LIGHT REACTIONS
CALVIN CYCLE REACTIONS
Are carried out by molecules in the thylakoid membranes
Convert light energy to the chemical energy of ATP and NADPH
Split H2O and release O2
Take place in the stroma
Use ATP and NADPH to convert CO2 to the sugar G3P
Return ADP, inorganic phosphate, and NADP+ to the light reactions
Figure A review of photosynthesis (part 2: light reactions vs calvin cycle)
© 2017 Pearson Education, Ltd.

50. Photosynthesis is one of many important processes conducted by a working plant cell
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51. MAKE CONNECTIONS: The Working Cell
Figure 8.20
MAKE CONNECTIONS: The Working Cell
Movement Across Cell Membranes
(Chapter 5)
DNA
Nucleus
mRNA
Nuclear
pore
Energy Transformations in the Cell:
Photosynthesis and Cellular
Respiration (Chapters 6-8)
Rough endoplasmic
reticulum (ER)
Protein
Protein
in vesicle
mRNA
Vacuole
Ribosome
Vesicle
forming
Photosynthesis
in chloroplast
CO2
Golgi
apparatus
H2O
Protein
ATP
Organic
molecules
Transport
pump
Plasma
membrane
ATP O2
Cellular respiration
in mitochondrion
ATP
Figure 8.20 Make connections: the working cell
ATP
Flow of Genetic
Information in the Cell:
DNA → RNA → Protein
(Chapters 3–5)
Cell wall O2
CO2
H2O
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52. Flow of Genetic Information in the Cell:
Figure
DNA
Nucleus
mRNA
Nuclear
pore
Rough endoplasmic
reticulum (ER)
Protein
Protein
in vesicle
Figure Make connections: the working cell (part 1)
mRNA
Ribosome
Flow of Genetic Information in the Cell:
DNA → RNA → Protein (Chapters 3-5)
© 2017 Pearson Education, Ltd.

53. Flow of Genetic Information in the Cell:
Figure
Vesicle
forming
Golgi
apparatus
Protein
Plasma
membrane
Figure Make connections: the working cell (part 2)
Cell wall
Flow of Genetic Information in the Cell:
DNA → RNA → Protein (Chapters 3-5)
© 2017 Pearson Education, Ltd.

54. Energy Transformations in the Cell: Photosynthesis
Figure
Photosynthesis
in chloroplast
CO2
H2O
ATP
Transport
pump
Organic
molecules
ATP O2
Cellular respiration
in mitochondrion
ATP
ATP
Movement Across Cell
Membranes
(Chapter 5)
Figure Make connections: the working cell (part 3)
Energy Transformations
in the Cell: Photosynthesis
and Cellular Respiration
(Chapters 6-8) O2
CO2
H2O
© 2017 Pearson Education, Ltd.

55. Figure 8.UN04-1
Figure 8.UN04-1 Skills exercise: making scatter plots with regression lines (part 1)
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56. by invasive velvetleaf plants
Figure 8.UN04-2
Corn plant surrounded
by invasive velvetleaf
plants
Figure 8.UN04-2 Skills exercise: making scatter plots with regression lines (part 2)
© 2017 Pearson Education, Ltd.

57. Electron transport chain Primary acceptor Electron transport Fd chain
Figure 8.UN05
Electron transport
chain
Primary
acceptor
Electron transport
chain Fd
Primary
acceptor
NADP+
NADP+
reductase
+ H+
H2O Pq
NADPH O2
Cytochrome
complex Pc
Figure 8.UN05 Summary of key concepts: linear electron flow
Photosystem I
ATP
Photosystem II
© 2017 Pearson Education, Ltd.

58. Calvin Cycle Regeneration of CO2 acceptor
Figure 8.UN06
3 CO2
Carbon fixation
3 x 5C
6 x 3C
Calvin
Cycle
Regeneration of
CO2 acceptor
Figure 8.UN06 Summary of key concepts: the Calvin cycle
5 x 3C
Reduction
1 G3P (3C)
© 2017 Pearson Education, Ltd.

59. Figure 8.UN07
pH 4
pH 7
pH 4
pH 8
Figure 8.UN07 Test your understanding, question 9 (thylakoids and pH)
ATP
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60. Figure 8.UN08 Test your understanding, question 14 (“watermelon snow”)
© 2017 Pearson Education, Ltd.