1. Overview: The Process That Feeds the Biosphere
Photosynthesis converts solar energy into chemical energy
Directly or indirectly, photosynthesis nourishes almost the entire living world

2. Autotrophs are the producers of the biosphere
Almost all plants are photoautotrophs, using the energy of sunlight to make organic molecules

3. Figure 10.1
Figure 10.1 How can sunlight, seen here as a spectrum of colors in a rainbow, power the synthesis of organic substances? 3

4. These organisms feed not only themselves but also most of the living world

5. BioFlix: Photosynthesis
© 2011 Pearson Education, Inc.

6. Figure 10.2
Almost all heterotrophs, including humans, depend on photoautotrophs for food and O2
(b)
Multicellular alga
(a) Plants
Figure 10.2 Photoautotrophs.
(d) Cyanobacteria
40 m
(c)
Unicellular protists
10 m
(e)
Purple sulfur bacteria
1 m 6

7. Figure 10.3 Impact: Alternative Fuels from Plants and Algae7

8. Photosynthesis converts light energy to the chemical energy of food
The structure and organization of plant cells allows for photosynthesis to occur thanks to chloroplasts

9. Chloroplasts: The Sites of Photosynthesis in Plants
Leaves are the major locations of photosynthesis
Their green color is from chlorophyll, the green pigment within chloroplasts

10. Chloroplasts
Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf
Each mesophyll cell contains 30–40 chloroplasts

11. Chloroplast Outer membrane Thylakoid Intermembrane space Stroma Granum
Figure 10.4b
Chloroplast
Outer membrane
Thylakoid
Intermembrane space
Stroma
Granum
Thylakoid space
Inner membrane
Figure 10.4 Zooming in on the location of photosynthesis in a plant.
1 m 11

12. Figure 10.4c
Mesophyll cell
Figure 10.4 Zooming in on the location of photosynthesis in a plant.
20 m 12

13. Tracking Atoms Through Photosynthesis: Scientific Inquiry
Photosynthesis is a complex series of reactions that can be summarized as the following equation:
6 CO H2O + Light energy  C6H12O6 + 6 O2 + 6 H2O
© 2011 Pearson Education, Inc.

14. The Splitting of Water
Chloroplasts split H2O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules and releasing oxygen as a by-product

15. Reactants: 6 CO2 12 H2O Products: C6H12O6 6 H2O 6 O2
Figure 10.5
Reactants:
6 CO2
12 H2O
Products:
C6H12O6
6 H2O
6 O2
Figure 10.5 Tracking atoms through photosynthesis. 15

16. Photosynthesis as a Redox Process
Photosynthesis reverses the direction of electron flow compared to respiration
Photosynthesis is an endergonic process; the energy boost is provided by light
becomes reduced
Energy  6 CO2  6 H2O
C6 H12 O6  6 O2
becomes oxidized

17. 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
Split H2O
Release O2
Reduce NADP+ to NADPH
Generate ATP from ADP by photophosphorylation

18. The Calvin cycle (in the stroma) forms sugar from CO2, using ATP and NADPH
The Calvin cycle begins with carbon fixation, incorporating CO2 into organic molecules

19. H2O Light NADP ADP + P i Light Reactions Chloroplast
Figure 10.6 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle.
Chloroplast 19

20. H2O Light NADP ADP + P i Light Reactions ATP NADPH Chloroplast O2
Figure 10.6 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle.
NADPH
Chloroplast O2 20

21. Calvin Cycle Light Reactions
H2O
CO2
Light
NADP
ADP
+ P i
Calvin Cycle
Light Reactions
ATP
Figure 10.6 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle.
NADPH
Chloroplast O2 21

22. Calvin Cycle Light Reactions [CH2O] (sugar)
CO2
Light
NADP
ADP
+ P i
Calvin Cycle
Light Reactions
ATP
Figure 10.6 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle.
NADPH
Chloroplast
[CH2O] (sugar) O2 22

23. The light reactions convert solar energy to the chemical energy of ATP and NADPH
Thylakoids turn light into chemical energy

24. The Nature of Sunlight Light is a form of electromagnetic energy
Wavelength determines the type of electromagnetic energy
Each color is seen due to them being different wavelengths

25. Gamma rays Micro- waves Radio waves
Figure 10.7
1 m
105 nm
103 nm
1 nm
103 nm
106 nm
(109 nm)
103 m
Gamma rays
Micro- waves
Radio waves
X-rays UV
Infrared
Visible light
Figure 10.7 The electromagnetic spectrum.
380
450
500
550
600
650
700
750 nm
Shorter wavelength
Longer wavelength
Higher energy
Lower energy 25

26. Photosynthetic Pigments: The Light Receptors
Reflected light
Light
Photosynthetic Pigments: The Light Receptors
Pigments are substances that absorb visible light
Wavelengths that are not absorbed are reflected or transmitted
Leaves appear green because chlorophyll reflects and transmits green light
Chloroplast
Absorbed light
Granum
Transmitted light

27. Animation: Light and Pigments
Right-click slide / select “Play”
© 2011 Pearson Education, Inc.

28. A spectrophotometer measures a pigment’s ability to absorb various wavelengths
This machine sends light through pigments and measures the fraction of light transmitted at each wavelength

29. Slit moves to pass light of selected wavelength. Green light
Figure 10.9
TECHNIQUE
Refracting prism
Chlorophyll solution
Photoelectric tube
White light
Galvanometer
High transmittance (low absorption): Chlorophyll absorbs very little green light.
Slit moves to pass light of selected wavelength.
Green light
Figure 10.9 Research Method: Determining an Absorption Spectrum
Low transmittance (high absorption): Chlorophyll absorbs most blue light.
Blue light 29

30. RESULTS
Chloro- phyll a
Chlorophyll b
absorption spectrum is a graph plotting a pigment’s light absorption versus wavelength
Absorption of light by chloroplast pigments
Carotenoids
(a)
Absorption spectra
400
500
600
700
Wavelength of light (nm)
Rate of photosynthesis (measured by O2 release)
action spectrum profiles the relative effectiveness of different wavelengths
(b) Action spectrum
400
500
600
700
Figure Inquiry: Which wavelengths of light are most effective in driving photosynthesis?
Aerobic bacteria
Filament of alga
Engelmann’s experiment
(c)
400
500
600
700 30

31. The action spectrum of photosynthesis was first demonstrated in 1883 by Theodor W. Engelmann
Areas receiving wavelengths favorable to photosynthesis produced excess O2
He used the growth of aerobic bacteria clustered along the alga as a measure of O2 production

32. Structure of Chlorophyll
CH3 in chlorophyll a
CH3
CHO in chlorophyll b
Structure of Chlorophyll
Porphyrin ring
Chlorophyll a is the main photosynthetic pigment
Accessory pigments, such as chlorophyll b, broaden the spectrum used for photosynthesis, or to absorb excess energy
Figure Structure of chlorophyll molecules in chloroplasts of plants.
Hydrocarbon tail (H atoms not shown) 32

33. Excitation of Chlorophyll by Light
When a pigment absorbs light, it goes from a ground state to an excited state, which is unstable
When excited electrons fall back to the ground state, photons are given off, an afterglow called fluorescence

34. Figure 10.12
Excited state e
Heat
Energy of electron
Photon (fluorescence)
Photon
Ground state
Chlorophyll molecule
Figure Excitation of isolated chlorophyll by light.
Fluorescence
If illuminated, an isolated solution of chlorophyll will fluoresce, giving off light and heat 34

35. 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) transfer the energy of photons to the reaction center

36. THYLAKOID SPACE (INTERIOR OF THYLAKOID)
Photosystem
Filled with various pigments
STROMA
Photon
Light- harvesting complexes
Reaction- center complex
Primary electron acceptor
REDOX e
Thylakoid membrane
Figure The structure and function of a photosystem.
Pigment molecules
Transfer of energy
Special pair of chlorophyll a molecules
THYLAKOID SPACE (INTERIOR OF THYLAKOID)
(a) How a photosystem harvests light 36

37. (b) Structure of photosystem II
Figure 10.13b
Chlorophyll
STROMA
Thylakoid membrane
Figure The structure and function of a photosystem.
Protein subunits
THYLAKOID SPACE
(b) Structure of photosystem II 37

38. 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

39. Light Reactions

40. The reaction-center chlorophyll a of PS II is called P680
Types of 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
It is P680+ naturally
Primary acceptor 2 e
P680
Figure How linear electron flow during the light reactions generates ATP and NADPH. 1
Light
Pigment molecules
Photosystem II (PS II) 40

41. P680+ Activation: Photolysis
P680+ is a very strong oxidizing agent
H2O is split by enzymes, and electrons are transferred from the H atoms to P680+ P680
O2 is released
Primary acceptor 2 e
H2O
2 H + 3
1/2 O2 e e
P680 1
Light
Figure How linear electron flow during the light reactions generates ATP and NADPH.
Pigment molecules
Photosystem II (PS II) 41

42. Electrons Are Passed Between Photosystems by ETC & Generate ATP
Energy released by “the fall” creates a proton gradient across thylakoid membrane
Diffusion of H+ (protons) across the membrane drives ATP synthesis 4
Primary acceptor
Electron transport chain 2
H2O Pq
2 H e + 3
Cytochrome complex e
1/2 O2 e Pc
Light 5
P680 1
Figure How linear electron flow during the light reactions generates ATP and NADPH.
ATP
Pigment molecules
Photosystem II (PS II) 42

43. PSI Accepts Electrons From PSII
Primary acceptor
Reaction Center for PSI is P700
Primary acceptor 4
Electron transport chain Pq e 2 e
H2O
2 H
Cytochrome complex + 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)
Transferred light energy excites P700, which loses an electron to an electron acceptor, creating P700+ (ready to take on more e-) 43

44. Photosystem I Redox
The primary electron acceptor of PS I passes electrons to the protein ferredoxin (Fd)
The electrons are then transferred to NADP+ and reduce it to NADPH, for the reactions of the Calvin cycle
This process also removes an H+ from the stroma

45. Linear Electron Flow Electron transport chain Primary acceptor4 7
Electron transport chain Fd Pq e 2 e 8 e e
H2O
NADP
2 H
Cytochrome complex
NADP reductase
+ H + 3
1/2 O2
NADPH Pc e e
P700 5
P680
Light 1
Light 6
Figure How linear electron flow during the light reactions generates ATP and NADPH.
ATP
Pigment molecules
Photosystem I (PS I)
Photosystem II (PS II) 45

46. Light Reaction: Review

47. Mill makes ATP NADPH ATP Photosystem II Photosystem I e e e e e
Photon
Figure A mechanical analogy for linear electron flow during the light reactions. e
ATP
Photon
Photosystem II
Photosystem I 47

48. Only photosystem I used: produces ATP, but not NADPH, no O2 released
Cyclic Electron Flow
Primary acceptor
Primary acceptor Fd Fd
NADP + H Pq
NADP reductase
Cytochrome complex
NADPH Pc
Figure Cyclic electron flow.
Photosystem I
Photosystem II
ATP
Only photosystem I used: produces ATP, but not NADPH, no O2 released 48

49. Some organisms such as purple sulfur bacteria have PS I but not PS II
Cyclic electron flow is thought to have evolved before linear electron flow
Cyclic electron flow may protect cells from light-induced damage

50. 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
Spatial organization of chemiosmosis differs between chloroplasts and mitochondria but also shows similarities

51. Electron transport chain
Figure 10.17
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
ADP  P i
ATP
Key
Higher [H ] H
Lower [H ] 51

52. STROMA (low H concentration) Cytochrome complex NADP reductase
Figure 10.18
STROMA (low H concentration)
Cytochrome complex
NADP reductase
Photosystem II
Photosystem I
Light 3
Light
4 H+
NADP + H Fd Pq
NADPH 2 Pc
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
ADP + P i
ATP
STROMA (low H concentration) H+ 52

53. The Light Reactions: in Summary
ATP and NADPH are produced on the side facing the stroma, where the Calvin cycle takes place
In summary, light reactions generate ATP and increase the potential energy of electrons by moving them from H2O to NADPH

54. The Calvin Cycle
Generates sugars and starting materials through the use of ATP and electrons from NADPH

55. 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 1 G3P, the cycle must take place three times, fixing 3 molecules of CO2
The Calvin cycle has three phases
Carbon fixation (catalyzed by rubisco)
Reduction
Regeneration of the CO2 acceptor (RuBP)

56. Ribulose – 1,5 bisphosphate Carboxylase/Oxygenase
RuBisCO
The Rubisco enzyme is the most common enzyme on the planet!
Vital for Glucose formation!

57. Figure 10.19 The Calvin cycle.
Input 3
(Entering one at a time)
CO2
Phase 1: Carbon fixation
Rubisco 3 P P
Short-lived intermediate 3 P P 6 P
Ribulose bisphosphate (RuBP)
3-Phosphoglycerate
Figure The Calvin cycle. 57

58. Figure 10.19 The Calvin cycle.
Input 3
(Entering one at a time)
CO2
Phase 1: Carbon fixation
Rubisco 3 P P
Short-lived intermediate 3 P P 6 P
Ribulose bisphosphate (RuBP)
3-Phosphoglycerate 6
ATP
6 ADP
Calvin Cycle 6 P P
1,3-Bisphosphoglycerate
6 NADPH
6 NADP
6 P i
Figure The Calvin cycle. 6 P
Glyceraldehyde 3-phosphate (G3P)
Phase 2: Reduction 1 P
G3P (a sugar)
Glucose and other organic compounds
Output 58

59. Figure 10.19 The Calvin cycle.
Input 3
(Entering one at a time)
CO2
Phase 1: Carbon fixation
Rubisco 3 P P
Short-lived intermediate 3 P P 6 P
Ribulose bisphosphate (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 the CO2 acceptor (RuBP)
6 NADP
6 P i
Figure The Calvin cycle. 5 P
G3P 6 P
Glyceraldehyde 3-phosphate (G3P)
Phase 2: Reduction 1 P
G3P (a sugar)
Glucose and other organic compounds
Output 59

60. Calvin Cycle: Recap

61. 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 structures such as roots, tubers, seeds, and fruits
In addition to food production, photosynthesis produces the O2 in our atmosphere

62. H2O CO2 Light NADP ADP + P i Light Reactions: RuBP 3-Phosphoglycerate
Figure 10.22
H2O
CO2
Light
NADP
ADP
+ P i
Light Reactions:
Photosystem II Electron transport chain Photosystem I Electron transport chain
RuBP
3-Phosphoglycerate
Calvin Cycle
ATP
G3P
Figure A review of photosynthesis.
Starch (storage)
NADPH
Chloroplast O2
Sucrose (export) 62

63. Electron transport chain Electron transport chain
Figure 10.UN02
Primary acceptor
Electron transport chain
Primary acceptor
Electron transport chain Fd
NADP + H
H2O Pq
NADP reductase O2
Cytochrome complex
NADPH Pc
Figure 10.UN02 Summary figure, Concept 10.2
Photosystem I
ATP
Photosystem II 63

64. Regeneration of CO2 acceptor
Figure 10.UN03
3 CO2
Carbon fixation
3  5C
6  3C
Calvin Cycle
Regeneration of CO2 acceptor
5  3C
Figure 10.UN03 Summary figure, Concept 10.3
Reduction
1 G3P (3C) 64

65. Figure 10.UN04
pH 4
pH 7
pH 4
pH 8
Figure 10.UN04 Test Your Understanding, question 9
ATP 65

66. Figure 10.UN05
Figure 10.UN05 Appendix A: answer to Figure legend question 66

67. Figure 10.UN06
Figure 10.UN06 Appendix A: answer to Figure legend question 67

68. Figure 10.UN07
Figure 10.UN07 Appendix A: answer to Summary of Concept 10.3 Draw It question 68

69. Figure 10.UN08
Figure 10.UN08 Appendix A: answer to Test Your Understanding, question 9 69