Photosynthesis

1
Photosynthesis
2
Jan Baptisa van Helmont (1648)

• "...I took an earthenware vessel, placed in it
  200 pounds of soil dried in an oven, soaked this
  with rainwater, and planted in it a willow branch
  weighing 5 pounds. At the end of five years, the
  tree grown from it weighed 169 pounds and about 3
  ounces. Now, the earthenware vessel was always
  moistened (when necessary) only with rainwater or
  distilled water, and it was large enough and
  embedded in the ground, and, lest dust flying be
  mixed with the soil, an iron plate coated with
  tin and pierced by many holes covered the rim of
  the vessel. I did not compute the weight of the
  fallen leaves of the four autumns. Finally, I
  dried the soil in the vessel again, and the same
  200 pounds were found, less about 2 ounces.
  Therefore 169 pounds of wood, bark, and root had
  arisen from water only.
• 6CO2 6H2O Energy C6H12O6 6O2

3
Jan Baptisa van Helmont (1648)

• "...I took an earthenware vessel, placed in it
  200 pounds of soil dried in an oven, soaked this
  with rainwater, and planted in it a willow branch
  weighing 5 pounds. At the end of five years, the
  tree grown from it weighed 169 pounds and about 3
  ounces. Now, the earthenware vessel was always
  moistened (when necessary) only with rainwater or
  distilled water, and it was large enough and
  embedded in the ground, and, lest dust flying be
  mixed with the soil, an iron plate coated with
  tin and pierced by many holes covered the rim of
  the vessel. I did not compute the weight of the
  fallen leaves of the four autumns. Finally, I
  dried the soil in the vessel again, and the same
  200 pounds were found, less about 2 ounces.
  Therefore 169 pounds of wood, bark, and root had
  arisen from water only.
• 6CO2 6H2O Energy C6H12O6 6O2

4
Electromagnetic Spectrum
Visible light is only a part of the
electromagnetic spectrum.
nanometers
10-5
10-3
1
103
106
1 m
103 m
Gamma rays
X-rays
UV
Infrared
Microwaves
Radio waves
Visible light
5
Wavelength
Light travels in waves. The color of light is
determined by its wavelength. The red light shown
below has a wavelength of 700 nm.
700 nm
Red Blue
470 nm
Notice that blue light has a shorter wavelength.
Light Pigments Chloroplast Overview
Photosystems Photosystem II Electron
Transport System Photosystem I Calvin Cycle
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6
Electromagnetic Spectrum
nanometers
10-5
10-3
1
103
106
1 m
103 m
Gamma rays
X-rays
UV
Infrared
Microwaves
Radio waves
Visible light
7
Electromagnetic Spectrum
nanometers
10-5
10-3
1
103
106
1 m
103 m
Gamma rays
X-rays
UV
Infrared
Microwaves
Radio waves
The spectrum shown below fits into the small
space shown on the line.
Visible light
8
Photosynthetic Pigments
Light behaves as if it is composed of units or
packets called photons.
Plants have pigment molecules that contain atoms
that become energized when they are struck by
photons of light. Energized electrons move
further from the nucleus.
9
Photosynthetic Pigments
When the energy is released, the electron returns
to a location closer to the nucleus.
Heat or light
The energized molecule can transfer the energy to
another atom or molecule or release it in the
form of heat or light.
10
What color is best?

• In this experiment, a prism is used to produce a
  gradient of light that ranges from red to blue.
  The large cell is a photosynthetic alga called
  Spirogyra. The spiral-shaped green structure is
  its chloroplast.
• The bacteria (represented by dots) are aerobic,
  that is, they require oxygen.
• The slide was initially prepared so that there
  was no oxygen present in the water surrounding
  the alga.
• Photosynthesis produces oxygen and the bacteria
  congregate in areas where the most oxygen is
  produced, thus, the rate of photosynthesis is
  highest. Blue and Red light therefore produce the
  highest rate of photosynthesis.

Light Pigments Chloroplast Overview
Photosystems Photosystem II Electron
Transport System Photosystem I Calvin Cycle
Photorespiration C4 plants Review
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11
This graph shows the color of light absorbed by
three different kinds of photosynthetic pigments.
Notice that they do not absorb light that is in
the green to yellow range.
Chlorophyll a Chlorophyll b Carotenoids
absorption
400 500
600 700
Wavelength
Light Pigments Chloroplast Overview
Photosystems Photosystem II Electron
Transport System Photosystem I Calvin Cycle
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12
Two Kinds of Reactions

• The reactions of photosynthesis can be divided
  into two main categories
• The light reactions require light.
• The light-independent reactions occur either in
  the light or in the dark.
• As you view the rest of these slides, keep in
  mind that the goal of photosynthesis is to
  synthesize glucose.
• Carbon dioxide is reduced to glucose (see
  equation below). The electrons needed for this
  reduction come from water.
• The energy needed for this reduction comes from
  light.
• The equation isEnergy 6CO2 6H2O ? C6H12O6
  6O2

13
light
light reactions
ATP
NADPH
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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14
H2O
O2
light
light reactions
ATP
NADPH
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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15
H2O
O2
light
light reactions
ATP
NADPH
light-independent reactions (Calvin cycle)
C02
The reduction of CO2 to glucose occurs in the
light-independent reactions.
C6H12O6
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
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16
Chloroplast Structure
Stroma
Double membrane
Thylakoids
17
Elodea leaf X 400
The small green structures within the cells of
this plant are chloroplasts.
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
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18
H2O
O2
light
light reactions
ADP
ATP
NADPH
NADP
light-independent reactions (Calvin cycle)
C02
C6H12O6
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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19
Photosystem I and IILight Absorption
20
This drawing shows a magnified view of a part of
a thylakoid. The green area is the thylakoid and
the blue area is the stroma of the chloroplast.
Photosynthetic pigments embedded within the
membrane form a unit called an antenna.
Antenna
Stroma
Thylakoidmembrane
Light Pigments Overview Chloroplast
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21

• A pigment molecule within the antenna absorbs a
  photon of light energy.
• The energy from that pigment molecule is passed
  to neighboring pigment molecules and eventually
  makes its way to pigment molecule called the
  reaction center.
• When the reaction center molecule becomes excited
  (energized), it loses an electron to an electron
  acceptor.

Light energy
Thylakoidmembrane
Electron acceptor
Reaction center
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
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22

• As a result of gaining an electron (reduction),
  the electron acceptor becomes a high-energy
  molecule. Remember - its energy came from light.
• Energy is transferred with the electron.

Light energy
Thylakoidmembrane
Electron acceptor
Reaction center
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
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23
The antenna and electron acceptor are called a
photosystem. There are two kinds of photosystems
in plants called photosystem I and photosystem
II. Photosystem I is sometimes called P700 and
photosystem II is sometimes P680. The 680 and 700
designations refer to the wavelength of light
that they absorb best.
Photosystem
Antenna
Thylakoidmembrane
Electron acceptor
Reaction center
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
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24
In the diagrams that follow, the antenna will be
drawn as a single green circle and the electron
acceptor as a single red circle.
Photosystem
Antenna
Thylakoidmembrane
Electron acceptor
Reaction center
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
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25
Photosystem II
26
LightEnergy
Chloroplast
Photosystem II
Photosystem I
The three blue circles represent the electron
transport system. They are proteins embedded
within the thylakoid membrane. The first protein
receives the electron (and energy) from the
electron acceptor.
Stroma
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
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27
LightEnergy
Chloroplast
H
H
H
H
H
H
H
H
As a result of gaining an electron (reduction),
the first carrier of the electron transport
system gains energy. It uses some of the energy
to pump H into the thylakoid.
Thylakoids
Stroma
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
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28
LightEnergy
Chloroplast
H
H
H
H
H
H
H
The carrier then passes the electron to the next
carrier. Because it used some energy to pump H,
it has less energy (reducing capability) to pass
to the next H pump.
Thylakoids
Stroma
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
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29
LightEnergy
Chloroplast
H
H
H
H
H
H
H
H
This carrier uses some of the remainder of the
energy to pump more H into the thylakoid.
Thylakoids
Stroma
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
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30
LightEnergy
Chloroplast
H
H
H
H
H
H
H
H
The electron is passed to the next carrier which
also pumps H.
Thylakoids
Stroma
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
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31
LightEnergy
Chloroplast
H
H
H
H
H
H
H
H
The electron transport system functions to create
a concentration gradient of Hinside the
thylakoid.
Thylakoids
Stroma
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
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32
LightEnergy
Chloroplast
The concentration gradient of H is used to
synthesize ATP. ATP is produced from ADP and Pi
when hydrogen ions pass out of the thylakoid
through ATP synthase.
H
H
H
H
H
H
ATP ADP Pi
H
H
Thylakoids
Stroma
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
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33
LightEnergy
Chloroplast
This method of synthesizing ATP by using a H
gradient in the thylakoid is called
photophosphorylation.
H
H
H
H
H
H
ATP ADP Pi
H
H
Thylakoids
Stroma
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
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34
Photosystem I
35
LightEnergy
Chloroplast
H
H
H
H
H
H
ATP ADP Pi
H
H
At this point, the electron has little reducing
capability (little energy is left). It is passed
to the P700 antenna.
Thylakoids
Stroma
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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36
LightEnergy
Chloroplast
H
H
H
H
H
H
ATP ADP Pi
H
H
A pigment molecule in the P700 antenna absorbs a
photon of solar energy. The energy from that
molecule is passed to neighboring molecules
within the antenna. The energy is eventually
passed to the reaction center of this antenna.
Thylakoids
Stroma
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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37
LightEnergy
Chloroplast
H
H
H
H
H
H
ATP ADP Pi
H
H
As a result of being energized, the P700 reaction
center loses the electron to an electron acceptor.
Thylakoids
Stroma
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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38
LightEnergy
Chloroplast
NADP H NADPH
H
H
H
H
H
H
ATP ADP Pi
H
H
The acceptor passes it to NADP, which becomes
reduced to NADPH. According to the following
equation, NADP has the capacity to carry two
electrons. NADP 2e- H ? NADPH
Thylakoids
Stroma
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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39
LightEnergy
Chloroplast
NADP H NADPH
H
H
H
H
H
H
ATP ADP Pi
H
H
The electron that was initially lost by
photosystem II (P680) must be replaced.
Thylakoids
Stroma
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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40
LightEnergy
Chloroplast
NADP H NADPH
H
H
H
H
H
H
ATP ADP Pi
H
H2O?2e- 2H ½ O2
Light Dependent Reaction Review
H
A hydrogen atom contains one electron (e-) and
one proton (H). The two hydrogen atoms in a
water molecule can therefore be used to produce
2e- and 2H.
Thylakoids
Stroma
Return
41
NADPH NADP
light
e- acceptor
e- acceptor
ATP
This diagram traces the path followed by an
electron during the light reactions. The path is
indicated by red arrows and letters. The
high-energy parts of the pathway are drawn near
the top of the diagram.
electrontransportsystem
P700 antenna complex
P680 antenna complex
H2O ? 2e- 2H O
Light Pigments Chloroplast Overview
Photosystem II Electron Transport System
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42
LightEnergy
Chloroplast
NADP H NADPH
CO2
H
Calvin Cycle
H
H
H
H
H
ATP ADP Pi
H
H2O?2e- 2H ½ O2
H
glucose
The next several slides show how the products of
the light reactions (ATP and NADPH) are used to
reduce CO2 to carbohydrate in the Calvin cycle.
Thylakoids
Stroma
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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43
LightEnergy
Chloroplast
NADP H NADPH
CO2
H
Calvin Cycle
H
H
H
H
H
ATP ADP Pi
H
H2O?2e- 2H ½ O2
H
glucose
The reactions of the Calvin cycle occur in the
stroma of the chloroplast.
Thylakoids
Stroma
Light Pigments Overview Chloroplast
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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44
H2O
O2
light
light reactions
ADP
ATP
NADPH
NADP
light-independent reactions (Calvin cycle)
C02
C6H12O6
Light Pigments Chloroplast Overview
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
Return
45
CO2 Fixation

• CO2 fixation refers to bonding CO2 to an organic
  molecule to make a larger molecule.
• C5 CO2 ? C6

46
CO2 Fixation
6 CO2
6 C-C-C-C-C-C
RuBP Carboxylase (rubisco)
6 C-C-C-C-C
CO2 fixation refers to bonding CO2 to an organic
molecule to make a larger molecule. Each CO2 is
bonded to ribulose biphosphate (RuBP). C5 CO2 ?
C6
Light Pigments Chloroplast Overview
Photosystem II Electron Transport System
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47
C3 Photosynthesis
6 CO2
6 C-C-C-C-C-C
RuBP Carboxylase (rubisco)
PGA
RuBP
6 C-C-C-C-C
12 C-C-C
Light Pigments Chloroplast Overview
Photosystem II Electron Transport System
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48
6 CO2
6 C-C-C-C-C-C
RuBP Carboxylase (rubisco)
PGA
RuBP
6 C-C-C-C-C
12 C-C-C
PGAL
12 C-C-C
The two molecules of PGA are reduced to form PGAL
(phosphoglyceraldehyde).
Light Pigments Chloroplast Overview
Photosystem II Electron Transport System
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49
6 CO2
6 C-C-C-C-C-C
RuBP Carboxylase (rubisco)
PGA
RuBP
6 C-C-C-C-C
12 C-C-C
12 ATP
PGAL
12 C-C-C
12 ADP P
12 NADPH
12 NADP
Light Pigments Chloroplast Overview
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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50
6 CO2
6 C-C-C-C-C-C
RuBP Carboxylase (rubisco)
PGA
RuBP
6 C-C-C-C-C
12 C-C-C
6 ADP P 6 ATP
10 C-C-C
12 ATP
PGAL
12 C-C-C
12 ADP P
12 NADPH
Glucose
C-C-C-C-C-C
12 NADP
Light Pigments Chloroplast Overview
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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51
6 CO2
6 C-C-C-C-C-C
RuBP Carboxylase (rubisco)
PGA
RuBP
6 C-C-C-C-C
12 C-C-C
6 ADP P 6 ATP
10 C-C-C
12 ATP
PGAL
12 C-C-C
12 ADP P
12 NADPH
Glucose
C-C-C-C-C-C
12 NADP
Light Pigments Chloroplast Overview
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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52
6 CO2
6 C-C-C-C-C-C
RuBP Carboxylase (rubisco)
PGA
RuBP
6 C-C-C-C-C
12 C-C-C
6 ADP P 6 ATP
10 C-C-C
12 ATP
PGAL
12 C-C-C
12 ADP P
12 NADPH
Glucose
C-C-C-C-C-C
12 NADP
Light Pigments Chloroplast Overview
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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53
H2O
O2
light
Light reactions
ADP
ATP
NADPH
NADP
Light-independent reactions
C02
Click Here for Calvin Review
C6H12O6
Light Pigments Chloroplast Overview
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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54
Photorespiration Alternative Carbon Fixations

• Evolutionary Adaptation
• Trade Off
• Compromise b/w photosynthesis and loss of water
• CO2 enter leaf through stomatas (pores)
• Stomatas also allow water to evaporate
• Close stomata, limit water loss AND CO2 intake

55
CO2 Fixation
6 CO2
6 C-C-C-C-C-C
RuBP Carboxylase (rubisco)
RuBP
6 C-C-C-C-C
12 C-C-C
10 C-C-C
12 C-C-C
C-C-C-C-C-C
Light Pigments Chloroplast Overview
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
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56
Cross Section of a C3 Leaf
Stomata (singular stoma) are microscopic openings
on the undersurface of leaves that allow gas
exchange and water evaporation from inside the
leaf. Because dehydration can be a serious
problem, the stomata close when the plant is
under water stress. When closed, CO2 needed for
the Calvin cycle cannot enter.
mesophyll cells
bundle-sheath cells
vein
stoma
57
If CO2 is low
6 CO2
CO2
6 C-C-C-C-C-C
O2
RUBISCO
RuBP
6 C-C-C-C-C
Evolutionary relic Rice, Wheat, Soybean
When the concentration of CO2 is low (red above),
oxygen will bind to the active site of RUBISCO.
When oxygen is bound to RUBISCO, RuBP is broken
down and CO2 is released.  This wastes energy and
is of no use to the plant. It is called
photorespiration because oxygen is taken up and
CO2 is released.
Light Pigments Chloroplast Overview
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
C4 plants Review
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58
Cross Section of a C3 Leaf
Photosynthesis occurs within the mesophyll cells
in C3 plants, which form a dense layer on the
upper surface of the leaf and a spongy layer on
the lower surface. Bundle-sheath cells
surrounding the veins are not photosynthetic.
mesophyll cells
bundle-sheath cells
vein
stoma
59
C4 Plants

• Preface Calvin Cycle with alternative mode of
  Carbon Fixation
• Sugarcane, corn

60
Cross Section of a C4 Leaf
Sugar cane and Corn
mesophyll cells
bundle-sheath cells
vein
stoma
61
CO2 Fixation in C4 Plants

• CO2 fixation occurs in mesophyll cells

62
CO2 Fixation in C4 Plants

• CO2 fixation occurs in mesophyll cells
• Calvin cycle occurs in bundle sheath cells

C3 PEP carboxylase C4 Oxaloacetate then
convert to Malate C3 Pyruvate
63
C4 Plants
64
CAM Plants vrs. C4
65
CAM Plants Arid Conditions/succulent plants
CAM crassulacean acid metabolism Crassulaceae
are a family of plants where CAM was first
discovered. Mesophyll stores organic acid during
night in vacoules until morning Light Rxn
supplies ATP and NADPH (for Calvin Cycle), CO2
released From organic acid in mesophyll.
66
Review Exercises
67
Identify components A through D.

• ADP Pi
• ATP
• Energy

A
B
C
D
68

• NADP
• NADPH H
• Energy 2H

A
B
C
D
69
Identify
H
I
ADP Pi ATP Calvin cycle CO2 glucose
phosphate light NADP NADPH oxygen water
A
light reactions
D
B
C
E
F
J
G
Light Pigments Chloroplast Overview
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70

• Where do the light reactions occur?
• Where do the light-independent reactions occur?

light
light reactions
ADP
H2O ? 2H 2e- O
ATP
NADPH
NADP
light-independent reactions (Calvin cycle)
C02
C-C-C-C-C-C
Light Pigments Chloroplast Overview
Photosystem II Electron Transport System
Photosystem I Calvin Cycle Photorespiration
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71
How many carbon atoms?
G
Light Pigments Chloroplast Overview
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72
Identify each component.
73
Fill in the Boxes below.
Light Reactions
Light-Independent Reactions
Inputs
Produced
74
Fill in the Boxes below.
Light Reactions
Light-Independent Reactions
light, ADP, NADP, H2O
Inputs
Produced
75
Fill in the Boxes below.
Light Reactions
Light-Independent Reactions
light, ADP, NADP, H2O
Inputs
ATP, NADPH, O2, H
Produced
76
Fill in the Boxes below.
Light Reactions
Light-Independent Reactions
light, ADP, NADP, H2O
ATP, NADPH, CO2
Inputs
ATP, NADPH, O2, H
Produced
77
Fill in the Boxes below.
Light Reactions
Light-Independent Reactions
light, ADP, NADP, H2O
ATP, NADPH, CO2
Inputs
glucose, ADP, NADP
ATP, NADPH, O2, H
Produced
78
The End