PowerLecture: Chapter 7

1
PowerLectureChapter 7

• Where It Starts - Photosynthesis

2
Section 7.0 Weblinks and InfoTrac

• See the latest Weblinks and InfoTrac articles for
  this chapter online or click highlighted articles
  below (articles subject to change)
• Section 7.0 ASU Center for the Study of Early
  Events in Photosynthesis
• Section 7.0 When Did Photosynthesis Emerge on
  Earth? David Des Marais, Science, Sept. 8, 2000.

3
How Would You Vote?

• The following is the question for this chapter.
  See the "Polls and ArtJoinIn" for this chapter if
  your campus uses a Personal Response System,or
  have your students vote online. See national
  results below.
• Should public funds be used to find potentially
  life supporting planets too far away for us to
  visit?

4
Impacts, Issues Sunlight and Survival

• Plants are autotrophs, or self-nourishing
  organisms
• The first autotrophs filled Earths 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

5
Sunlight and Survival
Fig. 7-1, p.106
6
Sunlight and Survival
p.107
7
Section 7.1 Weblinks and InfoTrac

• See the latest Weblinks and InfoTrac articles for
  this chapter online or click highlighted articles
  below (articles subject to change)
• Section 7.1 Chemistry of Autumn Colors
• Section 7.1 Molecule of the MonthChlorophyll
• Section 7.1 Foliage Afire Why Leaves Change
  Colors. Esther McGuire. New York State
  Conservationist, Oct. 1998.
• Section 7.1 Photochemistry of Chlorophyll.
  Bulletin of the South Carolina Academy of
  Science, 2002.

8
Electromagnetic Spectrum

• Shortest Gamma rays
• wavelength X-rays
• UV radiation
• Visible light
• Infrared radiation
• Microwaves
• Longest Radio waves
• wavelength

9
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)

10
Visible Light

• Wavelengths humans perceive as different colors
• Violet (380 nm) to red (750 nm)
• Longer wavelengths, lower energy

Figure 7-2Page 108
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Visible Light
shortest wavelengths (most energetic)
range of most radiation reaching Earths surface
range of heat escaping from Earths 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
12
Visible Light
Wavelengths of light
13
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

14
Variety of Pigments

• Chlorophylls a and b
• Carotenoids
• Anthocyanins
• Phycobilins

15
Chlorophylls

• Main pigments in most photoautotrophs

chlorophyll a
Wavelength absorption ()
chlorophyll b
Wavelength (nanometers)
16
Accessory Pigments
Carotenoids, Phycobilins, Anthocyanins
beta-carotene
phycoerythrin (a phycobilin)
percent of wavelengths absorbed
wavelengths (nanometers)
17
Pigments
Fig. 7-3a, p.109
18
Pigments
Fig. 7-3b, p.109
19
Pigments
Fig. 7-3c, p.109
20
Pigments
Fig. 7-3d, p.109
21
Pigments
Fig. 7-3e, p.109
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Pigments in Photosynthesis

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

23
Section 7.2 Weblinks and InfoTrac

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  below (articles subject to change)
• Section 7.2 Milestones in Photosynthesis
  Research
• Section 7.2 Photosynthetic Pigments in Bacteria
  and Plants
• Section 7.2 Sunlight at Southall Green. Norman
  Elaine Beale. Perspectives in Biology and
  Medicine, Summer 2001.
• Section 7.2 Photosynthesis and Respiration in a
  Jar. Joseph Buttner. Science Activities, Summer
  2000.

24
T.E. Englemanns Experiment

• Background
• Certain bacterial cells will move toward places
  where oxygen concentration is high
• Photosynthesis produces oxygen

25
T.E. Englemanns Experiment
26
T.E. Englemanns Experiment
Fig. 7-4a, p.110
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T.E. Englemanns Experiment
Fig. 7-4c, p.110
28
T.E. Englemanns Experiment
Fig. 7-5, p.110
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T.E. Englemanns Experiment

• Englemanns Experiment

30
Linked Processes

• Photosynthesis
• Energy-storing pathway
• Releases oxygen
• Requires carbon dioxide

• Aerobic Respiration
• Energy-releasing pathway
• Requires oxygen
• Releases carbon dioxide

31
Section 7.3 Weblinks and InfoTrac

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  below (articles subject to change)
• Section 7.3 MIT Biology HypertextbookPhysics of
  Photosynthesis

32
Chloroplast Structure
two outer membranes
stroma
inner membrane system
(thylakoids connected by channels)
Fig. 7-6, p.111
33
Photosynthesis Equation
LIGHT ENERGY
12H2O 6CO2
6O2 C2H12O6 6H2O
Water
Carbon Dioxide
Oxygen
Glucose
Water
In-text figurePage 111
34
Photosynthesis
Fig. 7-6a, p.111
35
Photosynthesis
leafs upper epidermis
photosynthetic cells
(see next slide)
vein
stoma (gap) across lower leaf epidermis
Fig. 7-6a, p.111
36
Photosynthesis
two outer membranes
thylakoid compartment
thylakoid membrane system inside stroma
stroma
Fig. 7-6b, p.111
37
Photosynthesis
SUNLIGHT
O2
CO2
H2O
NADPH, ATP
light-dependant reactions
light-independant reactions
NADP, ADP
sugars
CHLOROPLAST
Fig. 7-6c, p.111
38
Photosynthesis Equation

• Sites of Photosynthesis

39
Where Atoms End Up
40
Two Stages of Photosynthesis
sunlight
water uptake
carbon dioxide uptake
ATP
ADP Pi
LIGHT-INDEPENDENT REACTIONS
LIGHT-DEPENDENT REACTIONS
NADPH
NADP
glucose
P
oxygen release
new water
41
Arrangement of Photosystems
water-splitting complex
thylakoid compartment
H2O
2H  1/2O2
P680
P700
acceptor
acceptor
pool of electron carriers
stroma
PHOTOSYSTEM II
PHOTOSYSTEM I
42
Section 7.4 Weblinks and InfoTrac

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  below (articles subject to change)
• Section 7.4 Photosynthetic Antennas and Reaction
  Centers
• Section 7.4 The Amazing All-Natural Light
  Machine (light-harvesting molecule LH2). Mark
  Caldwell. scover, Dec. 1995.

43
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

44
Light-Dependent Reactions
photon
Photosystem
Light-Harvesting Complex
Fig. 7-7, p.112
45
Light-Dependent Reactions

• Noncyclic pathway of electron flow

46
LIGHT- HARVESTING COMPLEX
sunlight
PHOTOSYSTEM II
PHOTOSYSTEM I
H
NADPH
e-
e-
e-
e-
e-
e-
NADP H
e-
thylakoid compartment
H2O
H
H
H
H
H
H
H
H
H
H
O2
H
thylakoid membrane
stroma
ATP
ADP Pi
cross-section through a disk-shaped fold in the
thylakoid membrane
H
Fig. 7-8, p.113
47
Section 7.5 Weblinks and InfoTrac

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48
Photosystem Function Harvester Pigments

• Most pigments in photosystem are harvester
  pigments
• When excited by light energy, these pigments
  transfer energy to adjacent pigment molecules
• Each transfer involves energy loss

49
Pigments in a Photosystem
reaction center
50
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

51
Photo Energy

• Harvesting photo energy

52
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

53
Cyclic Electron Flow

• Electrons
• 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

54
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
55
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

56
Machinery of Noncyclic Electron Flow
H2O
second electron transfer chain
photolysis
e
e
ATP SYNTHASE
NADPH
first electron transfer chain
NADP
ATP
ADP Pi
PHOTOSYSTEM I
PHOTOSYSTEM II
57
Energy Changes
second
transfer
chain
e
NADPH
e
first
transfer
chain
Potential to transfer energy (volts)
e
e
(Photosystem I)
(Photosystem II)
1/2O2 2H
H2O
58
PHOTOSYSTEM I
p700
H
e-
photon
p700
Higher energy
Cyclic Pathway of ATP Formation
Fig. 7-9a, p.114
59
PHOTOSYSTEM I
NADPH
p700
PHOTOSYSTEM II
NADH
p680
e-
p700
photon
p680
2H2O
Noncyclic Pathway of ATP and NADPH Formation
4H O2
Fig. 7-9b, p.114
60
Energy Changes

• Energy changes in photosynthesis.

61
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

62
Chemiosmotic Model for ATP Formation
Gradients propel H through ATP synthases ATP
forms by phosphate-group transfer
H is shunted across membrane by some components
of the first electron transfer chain
Photolysis in the thylakoid compartment splits
water
H2O
e
acceptor
ATP SYNTHASE
ATP
ADP Pi
PHOTOSYSTEM II
63
Section 7.6 Weblinks and InfoTrac

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  this chapter online or click highlighted articles
  below (articles subject to change)
• Section 7.6 1961 Nobel PrizeMelvin Calvin
• Section 7.6 Biographical MemoirsMelvin Calvin
• Section 7.6 Robust Plants' Secret? Rubisco
  Activase! Marcia Wood. Agricultural Research,
  Nov. 2002.
• Section 7.6 Revealing the Secrets of Old Sol's
  Sugar Factories. Wim Vermaas. World and I, Mar.
  1998.

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Light-Independent Reactions

• Synthesis part of photosynthesis
• Can proceed in the dark
• Take place in the stroma
• Calvin-Benson cycle

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Calvin-Benson Cycle

• Overall reactants
• Carbon dioxide
• ATP
• NADPH

• Overall products
• Glucose
• ADP
• NADP

Reaction pathway is cyclic and RuBP (ribulose
bisphosphate) is regenerated
66
Calvin- Benson Cycle
6
CO2 (from the air)
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
67
Calvin- Benson Cycle
THESE REACTIONS PROCEED IN THE CHLOROPLASTS
STROMA
Fig. 7-10a, p.115
68
Calvin- Benson Cycle
6CO2
ATP
12 PGA
6 RuBP
12
6 ADP
12 ADP
12 Pi
Calvin-Benson cycle
ATP
12
NADPH
4 Pi
12 NADP
12 PGAL
10 PGAL
1 Pi
phosphorylated glucose
1
Fig. 7-10b, p.115
69
Calvin- Benson Cycle

• Calvin-Benson cycle

70
Section 7.7 Weblinks and InfoTrac

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  this chapter online or click highlighted articles
  below (articles subject to change)
• Section 7.7 Botany Online PhotosynthesisC3,
  C4, and CAM
• Section 7.7 International Society of
  Crassulacean Acid Metabolism Research
• Section 7.7 CAM Photosynthesis Not Just for
  Desert Plants. Elia Ben-Ari. BioScience, Dec.
  1998.
• Section 7.7 Evolution of CAM and C4
  Carbon-Concentrating Mechanisms. Jon Keeley et
  al. International Journal of Plant Sciences, May
  2003.

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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

72
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

73
C3 Plants
Fig. 7-11a1, p.116
74
C3 Plants
upper epidermis
palisade mesophyll
spongy mesophyll
lower epidermis
stoma
leaf vein
air space
Basswood leaf, cross-section.
Fig. 7-11a2, p.116
75
C3 Plants
Stomata closed CO2 cant get in O2 cant get out
6 PGA 6 glycolate
Rubisco fixes oxygen, not carbon, in mesophyll
cells in leaf
RuBP
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
76
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

77
C4 Plants
Fig. 7-11b1, p.117
78
C4 Plants
upper epidermis
mesophyll cell
bundle- sheath cell
lower epidermis
Basswood leaf, cross-section.
Fig. 7-11b2, p.117
79
Stomata closed CO2 cant get in O2 cant get out
Carbon fixed in the mesophyll cell, malate
diffuses into adjacent bundle-sheath cell
oxaloacetate
PEP
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
80
CAM Plants

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

81
CAM Plants
Fig. 7-11c1, p.117
82
stoma
epidermis with thick cuticle
mesophyll cell
air space
CAM Plants
Fig. 7-11c2, p.117
83
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
84
CAM Plants

• C3-C4 comparison

85
Summary of Photosynthesis
LIGHT-INDEPENDENT REACTIONS
Figure 7-14Page 120
86
Summary of Photosynthesis
Photosynthesis overview
87
Section 7.8 Weblinks and InfoTrac

• See the latest Weblinks and InfoTrac articles for
  this chapter online or click highlighted articles
  below (articles subject to change)
• Section 7.8 NASAs Earth ObservatoryPhytoplankto
  n
• Section 7.8 The Plankton Net
• Section 7.8 A Model of Phytoplankton Blooms.
  Amit Huppert et al. The American Naturalist, Feb.
  2002.
• Section 7.8 Rust in the Wind (absence of
  phytoplankton in the ocean). Mary Beth Aberlin.
  The Sciences, MarchApril 1996.

88
Videos CNN

• Ask your Thomson Sales Representative for these
  volumes on CD or VHS
• Biology, 2002, Vol. 6, Algal Fuel (200)

89
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

90
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
91
Photoautotrophs

• Capture sunlight energy and use it to carry out
  photosynthesis
• Plants
• Some bacteria
• Many protistans

92
Photoautotrophs
Winter
SPAIN
NORTH AMERICA
ATLANTIC OCEAN
AFRICA
Spring
Fig. 7-13, p.119
93
Satellite Images Show Photosynthesis
Atlantic Ocean
 Photosynthetic activity in spring
Figure 7-13Page 119
94
light energy
12H2O 6CO2
6O2 C2H12O6 6H2O
Water
Carbon Dioxide
Oxygen
Glucose
Water
enzymes
p.120
95
sunlight
Light- Dependent Reactions
12H2O
6O2
ATP
NADP
ADP Pi
NADPH
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
96
Fig. 7-15, p.121
97
Fig. 7-16a, p.121
98
Fig. 7-16b, p.121