1. Chapter 10
Photosynthesis

2. The Process That Feeds the Biosphere
Photosynthesis is the process that converts solar energy into chemical energy
Directly or indirectly, photosynthesis nourishes almost the entire living world
Photosynthesis occurs in plants, algae, certain other protists, and some prokaryotes
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3. Autotrophs (producers) sustain themselves without eating anything derived from other organisms
Heterotrophs (consumers) obtain their organic material from other organisms
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4. Chloroplasts: The Sites of Photosynthesis in Plants
Their green color is from chlorophyll, the green pigment within chloroplasts
Gas exchange occurs through the stomata
Found mainly in mesophyll cells (interior tissue)
A typical mesophyll cell has 30–40 chloroplasts
Chlorophyll is in the membranes of thylakoids ; thylakoids stacked in columns = grana
Chloroplasts also contain stroma, a dense fluid
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5. Stroma Thylakoid space Thylakoid Fig. 10-3a Leaf cross section Vein
Mesophyll
Stomata
CO2 O2
Chloroplast
Mesophyll cell
Figure 10.3 Zooming in on the location of photosynthesis in a plant
Stroma
Thylakoid
space
Thylakoid
5 µm

6. Tracking Atoms Through Photosynthesis:
Photosynthesis can be summarized as the following equation:
6 CO H2O + Light energy  C6H12O6 + 6 O2 + 6 H2O
Photosynthesis is a redox process in which H2O is oxidized and CO2 is reduced
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7. The Two Stages of Photosynthesis: A Preview
Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part)
The light reactions (in the thylakoids):
Split H2O
Release O2
Reduce NADP+ to NADPH
Generate ATP from ADP by photophosphorylation
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8. The Calvin cycle (in the stroma)
Inputs: CO2, ATP and NADPH
Products: Glucose
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

9. i CO2 Light NADP+ ADP Calvin Cycle Light Reactions ATP NADPH
Fig
H2O
CO2
Light
NADP+
ADP + P i
Calvin
Cycle
Light
Reactions
ATP
Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
NADPH
Chloroplast
[CH2O]
(sugar) O2

10. Like other electromagnetic energy, light travels in waves
The Nature of Sunlight
Light is a form of electromagnetic energy, also called electromagnetic radiation
Like other electromagnetic energy, light travels in waves
Wavelength is the distance between crests of waves
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11. 1 m (109 nm) 10–5 nm 10–3 nm 1 nm 103 nm 106 nm 103 m Micro- waves
Fig. 10-6
1 m
(109 nm)
10–5 nm
10–3 nm
1 nm
103 nm
106 nm
103 m
Gamma
rays
Micro-
waves
Radio
waves
X-rays UV
Infrared
Visible light
Figure 10.6 The electromagnetic spectrum
380
450
500
550
600
650
700
750 nm
Shorter wavelength
Longer wavelength
Higher energy
Lower energy

12. Photosynthetic Pigments: The Light Receptors
Pigments = absorb visible light
Different pigments absorb different wavelengths
Wavelengths that are not absorbed are reflected or transmitted
Leaves appear green because chlorophyll reflects and transmits green light
Chlorophyll a = main photosynthetic pigment
Chlorophyll b = accessory pigments
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13. Light Reflected light Chloroplast Absorbed Granum light Transmitted
Fig. 10-7
Light
Reflected
light
Chloroplast
Figure 10.7 Why leaves are green: interaction of light with chloroplasts
Absorbed
light
Granum
Transmitted
light

14. A Photosystem: A Reaction-Center Complex Associated with Light-Harvesting Complexes
A photosystem consists of a reaction-center complex (a type of protein complex) surrounded by light-harvesting complexes
The light-harvesting complexes (pigment molecules bound to proteins) funnel the energy of photons to the reaction center
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15. When a pigment absorbs light, it goes from a ground state to an excited state, which is unstable
A primary electron acceptor in the reaction center accepts an excited electron from chlorophyll a
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

16. (INTERIOR OF THYLAKOID)
Fig
Photosystem
STROMA
Photon
Primary
electron
acceptor
Light-harvesting
complexes
Reaction-center
complex e–
Thylakoid membrane
Figure How a photosystem harvests light
Pigment
molecules
Transfer
of energy
Special pair of
chlorophyll a
molecules
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)

17. 2 photosystems in the thylakoid membrane
Photosystem II (PS II) functions first and is best at absorbing a wavelength of 680 nm
The reaction-center chlorophyll a of PS II is called P680
Photosystem I (PS I) is best at absorbing a wavelength of 700 nm
The reaction-center chlorophyll a of PS I is called P700
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18. Linear Electron Flow
During the light reactions, there are two possible routes for electron flow: cyclic and linear
Linear electron flow, the primary pathway, involves both photosystems and produces ATP and NADPH using light energy
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19. Diffusion of H+ (protons) across the membrane drives ATP synthesis
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

20. Fig
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
- H2O is split by enzymes and O2 is released as a by-product of this reaction
Primary
acceptor 2
H2O e–
2 H+ + O2 3
1/2 e– e–
P680 1
Light
Figure How linear electron flow during the light reactions generates ATP and NADPH
Pigment
molecules
Photosystem II
(PS II)

21. In PS I (like PS II), transferred light energy excites P700, which loses an electron to an electron acceptor
P700+ (P700 that is missing an electron) accepts an electron passed down from PS II via the electron transport chain
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22. Electron transport chain
Fig
Primary
acceptor
Primary
acceptor 4
Electron transport chain Pq e– 2
H2O e–
Cytochrome
complex
2 H+ + 3
1/2 O2 Pc e– e–
P700 5
P680
Light 1
Light 6
ATP
Figure How linear electron flow during the light reactions generates ATP and NADPH
Pigment
molecules
Photosystem I
(PS I)
Photosystem II
(PS II)

23. The electrons are then transferred to NADP+ and reduce it to NADPH
Each electron “falls” down an electron transport chain from the primary electron acceptor of PS I to the protein ferredoxin (Fd)
The electrons are then transferred to NADP+ and reduce it to NADPH
The electrons of NADPH are available for the reactions of the Calvin cycle
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

24. Electron transport chain
Fig
Electron
transport
chain
Primary
acceptor
Primary
acceptor 4 7
Electron transport chain Fd Pq e– 2 e– 8 e–
H2O e–
NADP+
+ H+
Cytochrome
complex
2 H+
NADP+
reductase + 3
1/2 O2
NADPH Pc e– e–
P700 5
P680
Light 1
Light 6 6
ATP
Figure How linear electron flow during the light reactions generates ATP and NADPH
Pigment
molecules
Photosystem I
(PS I)
Photosystem II
(PS II)

25. Electron Transport Chain Cyclic vs Linear Electron Flow
Cyclic Electron Flow
Cyclic electron flow uses only photosystem I and produces ATP, but not NADPH
Electron Transport Chain
Cyclic vs Linear Electron Flow
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26. H+ Diffusion Electron transport chain ADP + P
Fig
Mitochondrion
Chloroplast
MITOCHONDRION
STRUCTURE
CHLOROPLAST
STRUCTURE H+
Diffusion
Intermembrane
space
Thylakoid
space
Electron
transport
chain
Inner
membrane
Thylakoid
membrane
Figure Comparison of chemiosmosis in mitochondria and chloroplasts
ATP
synthase
Matrix
Stroma
Key
ADP + P i
ATP
Higher [H+] H+
Lower [H+]

27. Fig. 10-17 STROMA (low H+ concentration) Cytochrome complex
Photosystem II
Photosystem I
4 H+
Light
NADP+
reductase
Light Fd 3
NADP+ + H+ Pq
NADPH e– Pc e– 2
H2O 1
1/2 O2
THYLAKOID SPACE
(high H+ concentration)
+2 H+
4 H+ To
Calvin
Cycle
Figure The light reactions and chemiosmosis: the organization of the thylakoid membrane
Thylakoid
membrane
ATP
synthase
STROMA
(low H+ concentration)
ADP +
ATP P i H+

28. The Calvin cycle uses ATP and NADPH to convert CO2 to sugar
Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde-3-phospate (G3P)
For net synthesis of 1 G3P, the cycle must take place three times, fixing 3 molecules of CO2
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29. Electron transport chain
Fig
H2O
CO2
Light
NADP+
ADP + P i
Light
Reactions:
Photosystem II
Electron transport chain
Photosystem I
RuBP
3-Phosphoglycerate
Calvin
Cycle
ATP
G3P
Figure A review of photosynthesis
Starch
(storage)
NADPH
Chloroplast O2
Sucrose (export)

30. Electron transport chain Electron transport chain NADP+ + H+
Fig. 10-UN1
H2O
CO2
Primary
acceptor
Electron transport
chain
Primary
acceptor
Electron transport
chain Fd
NADP+
+ H+
H2O Pq
NADP+
reductase O2
Cytochrome
complex
NADPH Pc
Photosystem I
ATP
Photosystem II O2