1. PHOTOSYNTHESIS Chapter 7
Where It Starts - Photosynthesis

2. Impacts, Issues: Sunlight and Survival
Plants are autotrophs, or self-nourishing organisms
The first autotrophs filled Earth’s atmosphere with oxygen, creating an ozone (O3) layer
The ozone layer became a shield against deadly UV rays from the sun, allowing life to move out of the ocean

3. Electromagnetic Spectrum
Shortest Gamma rays wavelength X-rays UV radiation Visible light Infrared radiation Microwaves Longest Radio waves wavelength

4. Photons Packets of light energy
Each type of photon has fixed amount of energy
Photons having most energy travel as shortest wavelength (blue-violet light)

5. Visible Light Wavelengths humans perceive as different colors
Violet (380 nm) to red (750 nm)
Longer wavelengths, lower energy
Figure 7-2 Page 108

6. Visible Light Fig. 7-2, p.108 shortest wavelengths (most energetic)
range of most radiation
reaching Earth’s surface
range of heat escaping
from Earth’s surface
longest wavelengths
(lowest energy)
gamma rays x
rays
ultraviolet
radiation
near-infrared
radiation
infrared
radiation
radio
waves
microwaves
VISIBLE LIGHT
400
450
500
550
600
650
700
Wavelengths of light (nanometers)
Fig. 7-2, p.108

7. Pigments Color you see is the wavelengths not absorbed
Light-catching part of molecule often has alternating single and double bonds
These bonds contain electrons that are capable of being moved to higher energy levels by absorbing light

8. Chlorophylls a and b Carotenoids Anthocyanins Phycobilins
Variety of Pigments
Chlorophylls a and b Carotenoids Anthocyanins Phycobilins

9. Wavelength absorption (%) Wavelength (nanometers)
Chlorophylls
Main pigments in most photoautotrophs
Wavelength absorption (%)
chlorophyll a
chlorophyll b
Wavelength (nanometers)

10. Accessory Pigments Carotenoids, Phycobilins, Anthocyanins
beta-carotene
phycoerythrin (a phycobilin)
percent of wavelengths absorbed
wavelengths (nanometers)

11. Pigments in Photosynthesis
Bacteria
Pigments in plasma membranes
Plants
Pigments and proteins organized into photosystems that are embedded in thylakoid membrane system

12. T.E. Englemann’s Experiment
Background
Certain bacterial cells will move toward places where oxygen concentration is high
Photosynthesis produces oxygen

13. T.E. Englemann’s Experiment

14. T.E. Englemann’s Experiment
Fig. 7-4c, p.110

15. Photosynthesis Aerobic Respiration Linked Processes
Energy-storing pathway
Releases oxygen
Requires carbon dioxide
Aerobic Respiration
Energy-releasing pathway
Requires oxygen
Releases carbon dioxide

16. Chloroplast Structure
two outer membranes
stroma
inner membrane system
(thylakoids connected by channels)
Fig. 7-6, p.111

17. Photosynthesis Equation
LIGHT ENERGY
12H2O + 6CO2
6O2 + C2H12O6 + 6H2O
Water
Carbon Dioxide
Oxygen
Glucose
Water
In-text figure Page 111

18. Photosynthesis
Fig. 7-6a, p.111

19. light-dependant reactions light-independant reactions
Photosynthesis
SUNLIGHT
H2O O2
CO2
NADPH, ATP
light-dependant reactions
light-independant reactions
NADP+, ADP
sugars
CHLOROPLAST
Fig. 7-6c, p.111

20. Where Atoms End Up
Reactants
12H2O
6CO2
Products
6O2
C6H12O6
6H2O

21. Two Stages of Photosynthesis
sunlight
water uptake
carbon dioxide uptake
ATP
LIGHT-DEPENDENT REACTIONS
ADP + Pi
LIGHT-INDEPENDENT REACTIONS
NADPH
NADP+ P
glucose
oxygen release
new water

22. Arrangement of Photosystems
water-splitting complex
thylakoid
compartment
H2O
2H + 1/2O2
P680
P700
acceptor
acceptor
pool of electron carriers
PHOTOSYSTEM II
stroma
PHOTOSYSTEM I

23. Light-Dependent Reactions
Pigments absorb light energy, give up e-, which enter electron transfer chains
Water molecules split, ATP and NADH form, and oxygen is released
Pigments that gave up electrons get replacements

24. Light-Dependent Reactions
photon
Photosystem
Light-Harvesting Complex
Fig. 7-7, p.112

25. cross-section through a disk-shaped fold in the thylakoid membrane
LIGHT-
HARVESTING
COMPLEX
PHOTOSYSTEM II
sunlight
PHOTOSYSTEM I H+
NADPH e- e- e- e- e- e-
NADP + + H+ e-
H2O H+ H+ H+ H+
thylakoid
compartment H+ H+ H+ H+ H+ H+ O2 H+
thylakoid
membrane
stroma
ADP + Pi
ATP
cross-section through a disk-shaped fold in the thylakoid membrane H+
Fig. 7-8, p.113

26. Pigments in a Photosystem
reaction center

27. Photosystem Function: Reaction Center
Energy is reduced to level that can be captured by molecule of chlorophyll a
This molecule (P700 or P680) is the reaction center of a photosystem
Reaction center accepts energy and donates electron to acceptor molecule

28. Electron Transfer Chain
Adjacent to photosystem
Acceptor molecule donates electrons from reaction center
As electrons pass along chain, energy they release is used to produce ATP

29. Cyclic Electron Flow Electrons Electron flow drives ATP formation
are donated by P700 in photosystem I to acceptor molecule
flow through electron transfer chain and back to P700
Electron flow drives ATP formation
No NADPH is formed

30. Cyclic Electron Flow e–
electron acceptor
Electron flow through transfer chain sets up conditions for ATP formation at other membrane sites.
electron transfer chain e– e–
ATP e–

31. Noncyclic Electron Flow
Two-step pathway for light absorption and electron excitation
Uses two photosystems: type I and type II
Produces ATP and NADPH
Involves photolysis - splitting of water

32. Machinery of Noncyclic Electron Flow
H2O
second electron transfer chain
photolysis e– e–
ATP SYNTHASE
first electron transfer chain
NADP+
NADPH
ATP
PHOTOSYSTEM II
PHOTOSYSTEM I
ADP + Pi

33. Potential to transfer energy (volts)
Energy Changes
second
transfer
chain e–
NADPH
first e–
transfer
chain
Potential to transfer energy (volts) e– e–
(Photosystem I)
(Photosystem II)
H2O
1/2O2 + 2H+

34. Cyclic Pathway of ATP Formation
PHOTOSYSTEM I
p700* H+ e-
photon
p700
Higher energy
Cyclic Pathway of ATP Formation
Fig. 7-9a, p.114

35. Noncyclic Pathway of ATP and NADPH Formation 4H+ + O2
PHOTOSYSTEM I
NADPH
p700*
PHOTOSYSTEM II
NADH+
p680* e-
photon
p700
p680
2H2O
Noncyclic Pathway of ATP
and NADPH Formation
4H+ + O2
Fig. 7-9b, p.114

36. Chemiosmotic Model of ATP Formation
Electrical and H+ concentration gradients are created between thylakoid compartment and stroma
H+ flows down gradients into stroma through ATP synthesis
Flow of ions drives formation of ATP

37. Chemiosmotic Model for ATP Formation
H+ is shunted across membrane by some components of
the first electron transfer chain
Gradients propel H+ through ATP synthases;
ATP forms by phosphate-group transfer
Photolysis in the thylakoid compartment splits water
H2O e–
acceptor
ATP SYNTHASE
ATP
ADP + Pi
PHOTOSYSTEM II

38. PHOTOSYNTHESIS QUIZ 1 1. Give the equation for photosynthesis.
2. Give the 2 major reactions occurring in photosynthesis.
3. What reactant goes into the light reactions? What product?
4. What reactant goes into the Calvin cycle? What product?
5. Within the chloroplast, where do the light reactions occur?
6. Within the chloroplast, where does the Calvin cycle occur?
7. What does noncyclic electron flow produce (besides ATP) that that cyclic electron flow does not produce?
8. Why doesn’t the overall action spectrum of photosynthesis exactly match the absorption spectrum for chlorophyll?
9. Which photosystem acts first in noncyclic electron flow?
****BONUS**** 1. What are Pq, Pc, and Fd?
2. Explain what chemiosmosis is.

39. Light-Independent Reactions
Synthesis part of photosynthesis
Can proceed in the dark
Take place in the stroma
Calvin-Benson cycle

40. Overall reactants Overall products Calvin-Benson Cycle Carbon dioxide
ATP
NADPH
Overall products
Glucose
ADP
NADP+
Reaction pathway is cyclic and RuBP (ribulose bisphosphate) is regenerated

41. unstable intermediate6
CO2 (from the air)
Calvin- Benson Cycle
CARBON FIXATION 6 6
RuBP
unstable intermediate 12
PGA
6 ADP 12
ATP 6
ATP 12
NADPH
4 Pi
12 ADP
12 Pi
12 NADP+ 10
PGAL 12
PGAL 2
PGAL Pi P
glucose

42. THESE REACTIONS PROCEED IN THE CHLOROPLAST’S STROMA
Calvin- Benson Cycle
THESE REACTIONS PROCEED IN THE CHLOROPLAST’S STROMA
Fig. 7-10a, p.115

43. phosphorylated glucose
Calvin- Benson Cycle
6CO2
ATP
6 RuBP
12 PGA 12
6 ADP
12 ADP +
Calvin-Benson
cycle
12 Pi
ATP 12
NADPH
4 Pi
12 NADP+
10 PGAL
12 PGAL
1 Pi 1
phosphorylated glucose
Fig. 7-10b, p.115

44. The C3 Pathway
In Calvin-Benson cycle, the first stable intermediate is a three-carbon PGA
Because the first intermediate has three carbons, the pathway is called the C3 pathway

45. Photorespiration in C3 Plants
On hot, dry days stomata close
Inside leaf
Oxygen levels rise
Carbon dioxide levels drop
Rubisco attaches RuBP to oxygen instead of carbon dioxide
Only one PGAL forms instead of two

46. C3 Plants
Fig. 7-11a1, p.116

47. C3 Plants upper epidermis palisade mesophyll spongy mesophyll lower
stoma
leaf vein
air space
Basswood leaf, cross-section.
Fig. 7-11a2, p.116

48. Twelve turns of the cycle, not just six, to
C3 Plants
Stomata closed: CO2 can’t get in; O2 can’t get out
Rubisco fixes oxygen, not carbon, in mesophyll cells in leaf
RuBP
6 PGA glycolate
Calvin-Benson
Cycle
5 PGAL
6 PGAL
CO2
+ water
1 PGAL
Twelve turns of the cycle, not just six, to
make one 6-carbon sugar
Fig. 7-11a3, p.117

49. C4 Plants Carbon dioxide is fixed twice
In mesophyll cells, carbon dioxide is fixed to form four-carbon oxaloacetate
Oxaloacetate is transferred to bundle-sheath cells
Carbon dioxide is released and fixed again in Calvin-Benson cycle

50. C4 Plants
Fig. 7-11b1, p.117

51. C4 Plants upper epidermis mesophyll cell bundle- sheath cell lower
Basswood leaf, cross-section.
Fig. 7-11b2, p.117

52. C4 Plants Stomata closed: CO2 can’t get in; O2 can’t get out
Carbon fixed in the mesophyll cell, malate diffuses into adjacent bundle-sheath cell
PEP
oxaloacetate
C4 Plants
C4 cycle
malate
pyruvate
CO2
In bundle-sheath
cell, malate gets converted to pyruvate with release of CO2, which enters Calvin-Benson cycle
RuBP
12 PGAL
Calvin-Benson
Cycle
10 PGAL
12 PGAL
2 PGAL
1 sugar
Fig. 7-11b3, p.117

53. CAM Plants Carbon is fixed twice (in same cells) Night Day
Carbon dioxide is fixed to form organic acids
Day
Carbon dioxide is released and fixed in Calvin-Benson cycle

54. CAM Plants
Fig. 7-11c1, p.117

55. CAM Plants stoma epidermis with thick cuticle mesophyll cell air space
Fig. 7-11c2, p.117

56. Stomata stay closed during day, open for CO2 uptake at night only.
CAM Plants
Stomata stay closed during day, open for CO2 uptake at night only.
C4 cycle operates at night when CO2 from aerobic respiration fixed
C4 CYCLE
CO2 that accumulated overnight used in C3 cycle during the day
Calvin-Benson
Cycle
1 sugar
Fig. 7-11c3, p.117

57. Summary of Photosynthesis
light
6O2
12H2O
CALVIN-BENSON CYCLE
C6H12O6
(phosphorylated glucose)
NADPH
NADP+
ATP
ADP + Pi
PGA
PGAL
RuBP P
6CO2
end product (e.g., sucrose, starch, cellulose)
LIGHT-DEPENDENT REACTIONS
6H2O
LIGHT-INDEPENDENT REACTIONS
Figure 7-14 Page 120

58. Carbon and Energy Sources
Photoautotrophs
Carbon source is carbon dioxide
Energy source is sunlight
Heterotrophs
Get carbon and energy by eating autotrophs or one another

59. Carbon and Energy Sources
glucose (stored energy, building blocks)
sunlight energy
Photosynthesis
Aerobic Respiration
1. H2O is split by light energy. Its oxygen diffuses away; its electrons, hydrogen enter transfer chains with roles in ATP formation. Coenzymes pick up the electrons and hydrogen
1. Glucose is broken down completely to carbon dioxide and water. Coenzymes pick up the electrons, hydrogens.
oxygen
2. The coenzymes give up the electrons and hydrogen atoms to oxygen-requiring transfer chains that have roles in forming many ATP molecules.
2. ATP energy drives the synthesis of glucose from hydrogen and electrons (delivered by coenzymes), plus carbon and oxygen (from carbon dioxide).
carbon dioxide,water
ATP available to drive nearly all cellular tasks
Fig. 7-12, p.118

60. Photoautotrophs
Capture sunlight energy and use it to carry out photosynthesis
Plants
Some bacteria
Many protistans

61. Satellite Images Show Photosynthesis
Atlantic Ocean
 Photosynthetic activity in spring
Figure 7-13 Page 119

62. phosphorylated glucose
sunlight
Light-
Dependent
Reactions
12H2O
6O2
ADP + Pi
ATP
NADPH
NADP+
6CO2
Calvin-Benson cycle
6 RuBP
12 PGAL
Light-
Independent
Reactions
6H2O
phosphorylated glucose
end products (e.g., sucrose, starch, cellulose)
Fig. 7-14, p.120

63. http://www. youtube. com/watch