Download Photosynthesis self

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
Glucose provides the energy and carbon needed to
synthesize other plant material.
1
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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
As can be seen from the equation for photosynthesis, the
wood, bark, and root arose from water and carbon
dioxide.
2
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Photosynthesis
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Before you start…
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
There are 83 slides in this presentation.
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shown.
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Light travels in waves. The color of light is
determined by its wavelength. The red light
shown below has a wavelength of 700 nm.
Wavelength
700 nm
Red
470 nm
Notice that blue light has a shorter wavelength.
Blue
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Electromagnetic Spectrum
Visible light is only a part of the
electromagnetic spectrum.
nanometers
10-5
10-3
Gamma
rays
103
1
X-rays
UV
106
Infrared
1m
Microwaves
103 m
Radio waves
Visible light
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Electromagnetic Spectrum
The numbers on this chart are
wavelength.
nanometers
10-5
10-3
Gamma
rays
103
1
X-rays
UV
106
Infrared
1m
Microwaves
103 m
Radio waves
Visible light
8
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Electromagnetic Spectrum
nanometers
10-5
10-3
Gamma
rays
103
1
X-rays
UV
106
Infrared
1m
Microwaves
103 m
Radio waves
The spectrum shown below fits into
the small space shown on the line.
Visible light
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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.
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Photosynthetic Pigments
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.
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Photosynthetic Pigments
Heat or light
When the energy is released, the electron
returns to a location closer to the nucleus.
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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 seen magnified under a microscope.
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, where the rate of
photosynthesis is highest. Blue and red light
therefore produce the highest rate of
photosynthesis.
Bacteria
Chloroplast of Spirogyra
Colors produced by a prism
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Absorption Spectrum
Chlorophyll a
absorption
Chlorophyll b
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.
Carotenoids
400
500
600
Wavelength
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700
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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). [Be sure that you
know what is meant by “reduced” before you go on.]
»
The electrons needed for this reduction come from water.
»
The energy needed for this reduction comes from light.
»
The equation is:
Energy + 6CO2 + 6H2O  C6H12O6 + 6O2
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Light Reactions
light
light reactions
ATP
NADPH
During photosynthesis, CO2 will be reduced (gain electrons) to
form glucose. The electrons needed to reduce CO2 are
temporarily carried by NADPH.
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H2O
light
O2
Light Reactions
light reactions
ATP
NADPH
Recall that hydrogen atoms can be used to carry
electrons. NADPH gets its electrons from water.
The oxygen is not used.
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H2O
light
Light-Independent Reactions
light reactions
ATP
C02
O2
NADPH
light-independent reactions
(Calvin cycle)
C6H12O6
The reduction of CO2 to glucose occurs
in the light-independent reactions.
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H2O
O2
Summary of Photosynthesis
light
light reactions
ATP
C02
This slide summarizes photosynthesis.
6CO2 + 6H2O + E  C6H12O6 + 6O2
NADPH
light-independent reactions
(Calvin cycle)
ADP
NADP+
C6H12O6
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Elodea leaf X 400
The small green structures within the
cells of this plant are chloroplasts.
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Chloroplast Structure
In order to understand the reactions of
photosynthesis, it will be helpful to review the
structure of a chloroplast. It contains diskshaped structures called thylakoids. The area
outside the disks is called the stroma.
Stroma
Double membrane
Thylakoids
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H2O
Summary of Photosynthesis
light
light reactions
ATP
C02
The next several slides will examine
the light reactions of photosynthesis.
O2
NADPH
light-independent reactions
(Calvin cycle)
ADP
NADP+
C6H12O6
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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
Thylakoid
membrane
Antenna
Photosynthetic pigments such as
chlorophyll A, chlorophyll B and carotinoids.
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Light energy
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.
Thylakoid
membrane
Reaction Center, Electron Acceptor
Electron acceptor
Reaction center
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Light energy
As a result of gaining an electron (reduction), the electron
acceptor becomes a high-energy molecule. Remember - its
energy came from light.
To understand this transfer of energy, recall that oxidation is
the loss of an electron and the loss of energy. Reduction is the
gain of an electron and energy. Energy is transferred with the
electron.
Thylakoid
membrane
Reaction Center, Electron Acceptor
Electron acceptor
Reaction center
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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
Thylakoid
membrane
Antenna, Photosystem
Electron acceptor
Reaction center
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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
Thylakoid
membrane
Antenna, Photosystem
Electron acceptor
Reaction center
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Light
Energy
Chloroplast
Electron Transport System
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
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Light
Energy
Chloroplast
Electron Transport System
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
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Light
Energy
Chloroplast
H+
+
H
Electron
Transport
System
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
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Light
Energy
Chloroplast
H+
H+
H+
H+
H+
H+
H+
H+
Electron Transport System
This carrier uses some of the remainder of the energy to pump more
H+ into the thylakoid.
Thylakoids
Stroma
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Light
Energy
Chloroplast
H+
H+
H+
H+
H+
H+
H+
H+
Electron Transport System
The electron is passed to the next carrier which also pumps H+.
Thylakoids
Stroma
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Light
Energy
Chloroplast
H+
H+
H+
H+
H+
H+
H+
H+
Electron Transport System
The electron transport system functions to create a concentration
gradient of H+inside the thylakoid.
Thylakoids
Stroma
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Light
Energy
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+
H+
Photophosphorylation
ATP
ADP + Pi
H+
Thylakoids
Stroma
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Light
Energy
Chloroplast
This method of synthesizing ATP by using a H+ gradient
in the thylakoid is called photophosphorylation.
H+
H+
H+
H+
H+
H+
H+
ATP
Photophosphorylation
ADP + Pi
H+
Thylakoids
Stroma
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Light
Energy
Chloroplast
H+
H+
H+
H+
H+
H+
H+
Photosystem I
ATP
ADP + Pi
H+
At this point, the electron has little reducing capability
(little energy is left). It is passed to the P700 antenna.
Thylakoids
Stroma
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Light
Energy
Chloroplast
H+
H+
H+
H+
H+
H+
ATP
H+
P700 Antenna
ADP + Pi
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
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Light
Energy
Chloroplast
H+
H+
H+
H+
H+
H+
H+
Electron Acceptor
ATP
ADP + Pi
H+
As a result of being energized, the P700 reaction
center loses the electron to an electron acceptor.
Thylakoids
Stroma
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Light
Energy
Chloroplast
NADP+ + H+
NADPH
H+
H+
H+
H+
H+
H+
H+
NADP+
ATP
ADP + Pi
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
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Light
Energy
Chloroplast
NADP+ + H+
NADPH
H+
H+
H+
H+
H+
H+
H+
ATP
ADP + Pi
Splitting H2O
H+
The electron that was initially lost by
photosystem II (P680) must be replaced.
Thylakoids
Stroma
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Light
Energy
Chloroplast
NADP+ + H+
NADPH
H+
H+
H+
H+
H+
H+
H+
H2O2e- + 2H+ + ½ O2
Splitting H2O
ATP
ADP + Pi
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
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e-
light
acceptor
e- acceptor
NADPH
NADP+
ATP
electron
transport
system
This diagram traces the path
followed by an electron
during the light reactions.
The path is indicated by red
arrows and letters. The highenergy parts of the pathway
are drawn near the top of
the diagram.
P700 antenna
complex
Summary of Light Reactions
P680 antenna
complex
H2O  2e- + 2H+ + O
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Light
Energy
Chloroplast
NADP+ + H+
CO2
NADPH
H+
H+
H+
H+
H+
H2O2e- + 2H+ + ½ O2
H+
H+
Calvin Cycle
Calvin
Cycle
ATP
ADP + Pi
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
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Light
Energy
Chloroplast
NADP+ + H+
CO2
NADPH
H+
H+
H+
H+
H+
H+
H+
H2O2e- + 2H+ + ½ O2
Calvin Cycle
Calvin
Cycle
ATP
ADP + Pi
H+
glucose
The reactions of the Calvin cycle occur in the stroma of the chloroplast.
Thylakoids
Stroma
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H2O
Light
Energy
O2
Chloroplast
NADP+ + H+
light
Summary of Photosynthesis
NADPH
H+
H+ +
H H+
H+ H +
H2O2e- + 2H+ + ½ O2
H+
ATP
ADP + Pi
H+
Thylakoids
light reactions
Stroma
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ATP
C02
NADPH
ADP
NADP+
light-independent reactions
(Calvin cycle)
C6H12O6
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CO2 Fixation

CO2 fixation refers to bonding CO2 to an organic molecule to make a larger molecule.

C5 + CO2  C6
“C5” is an abbreviation that means that this molecule has 5
carbon atoms. The oxygen and hydrogen atoms are not written.
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CO2 Fixation
6 CO2
6 C-C-C-C-C-C
RuBP
Carboxylase
(rubisco)
The enzyme that catalyzes this reaction is
ribulose biphosphate 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
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C3 Photosynthesis – Calvin Cycle
6 CO2
6 C-C-C-C-C-C
RuBP
Carboxylase
(rubisco)
RuBP 6 C-C-C-C-C
PGA 12 C-C-C
Each of these 6-carbon compounds splits to form
two 3-carbon compounds called phosphoglycerate.
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Calvin Cycle
6 CO2
6 C-C-C-C-C-C
RuBP
Carboxylase
(rubisco)
RuBP 6 C-C-C-C-C
PGA 12 C-C-C
PGAL
12 C-C-C
The two molecules of PGA are reduced to
form PGAL (phosphoglyceraldehyde).
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Calvin Cycle
6 CO2
6 C-C-C-C-C-C
RuBP
Carboxylase
(rubisco)
RuBP 6 C-C-C-C-C
PGA 12 C-C-C
PGAL
12 C-C-C
12 ATP
12 ADP + P
12 NADPH
12 NADP+
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Calvin Cycle
6 CO2
6 C-C-C-C-C-C
RuBP
Carboxylase
(rubisco)
RuBP 6 C-C-C-C-C
PGA 12 C-C-C
6 ADP + P
Two of the PGAL are used6toATP
form glucose phosphate, then glucose.
10 C-C-C
PGAL
12 C-C-C
12 ATP
12 ADP + P
12 NADPH
C-C-C-C-C-C Glucose
12 NADP+
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Calvin Cycle
6 CO2
6 C-C-C-C-C-C
RuBP
Carboxylase
(rubisco)
RuBP 6 C-C-C-C-C
PGA 12 C-C-C
6 ADP + P
The remaining 10 PGAL are
rearranged to form 6 RuBP.
6 ATP
10 C-C-C
PGAL
12 C-C-C
12 ATP
12 ADP + P
12 NADPH
C-C-C-C-C-C Glucose
12 NADP+
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Calvin Cycle
6 CO2
6 C-C-C-C-C-C
RuBP
Carboxylase
(rubisco)
RuBP 6 C-C-C-C-C
PGA 12 C-C-C
6 ADP + P
6 ATP
This process requires
energy in the form of ATP.
10 C-C-C
PGAL
12 C-C-C
12 ATP
12 ADP + P
12 NADPH
C-C-C-C-C-C Glucose
12 NADP+
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H2O
Light
Energy
Chloroplast
Summary of Photosynthesis
NADP+ + H+
light
O2
NADPH
H+
H+ +
H H+
H+ H +
Light reactions
ATP
H+
H2O2e- + 2H+ + ½ O2
ADP + Pi
H+
Thylakoids
Stroma
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ATP
NADPH
ADP
NADP+
6 CO2
C02
6 C-C-C-C-C-C
RuBP
Carboxylase
(rubisco)
6 C-C-C-C-C RuBP
6 ADP + P
6 ATP
10 C-C-C
PGAL
12 C-C-C
PGA 12 C-C-C
12 ATP
12 ADP + P
12 NADPH
C-C-C-C-C-C
Glucose
Light-independent
reactions
12 NADP+
C6H12O6
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End of Part 1

Please go back and review these slides and the information on photosynthesis before
continuing.

When you are ready to resume, select “Photorespiration” on the menu.
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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
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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
stoma
vein
bundle-sheath
cells
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If CO2 is low
6 CO2
CO2
O2
6 C-C-C-C-C-C
RUBISCO
RuBP 6 C-C-C-C-C
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.
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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
stoma
vein
bundle-sheath
cells
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Cross Section of a C4 Leaf
bundle-sheath
cells
vein
mesophyll
cells
stoma
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CO2 Fixation in C4 Plants

CO2
CO2 fixation occurs in
mesophyll cells
C3
C4
mesophyll cells
Calvin
cycle
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CO2 Fixation in C4 Plants
CO2
C3

CO2 fixation occurs in
mesophyll cells

Calvin cycle occurs in
bundle sheath cells
C3
C4
CO2
Calvin
cycle
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Review Exercises
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Review – ATP
Identify components A through D.
A
ADP + Pi
ATP
Energy
B
C
D
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Review – NADPH
NADP+
NADPH + H+
Energy + 2H
A
B
C
D
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Review – Summary of Photosynthesis
H
I
Identify:
A
light reactions
ADP + Pi
ATP
Calvin cycle
CO2
glucose phosphate
light
NADP+
NADPH
oxygen
water
D
B
F
C
E
J
G
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Review – Chloroplast Structure

Where do the light reactions occur?

Where do the light-independent reactions occur?
light
H2O  2H+ 2e- + O
C02
light reactions
ADP
ATP
NADPH
NADP+
light-independent reactions
(Calvin cycle)
C-C-C-C-C-C
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Review – Calvin Cycle
How many carbon atoms?
6A
6C
12 D
6B
10 F
12 E
G
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Review – Calvin Cycle
Identify each component.
6A
6C
12 D
6B
6L
12 H
6M
10 F
12 I
12 E
12 K
12 J
G
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Review – Inputs and Products
Fill in the Boxes below.
Light Reactions
Light-Independent
Reactions
Inputs
Produced
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Review – Inputs and Products
Fill in the Boxes below.
Light Reactions
Inputs
Light-Independent
Reactions
light, ADP,
NADP+, H2O
Produced
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Review – Inputs and Products
Fill in the Boxes below.
Light Reactions
Inputs
light, ADP,
NADP+, H2O
Produced
ATP, NADPH,
O2 , H +
Light-Independent
Reactions
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Review – Inputs and Products
Fill in the Boxes below.
Light Reactions
Inputs
light, ADP,
NADP+, H2O
Produced
ATP, NADPH,
O2 , H +
Light-Independent
Reactions
ATP, NADPH, CO2
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Review – Inputs and Products
Fill in the Boxes below.
Light Reactions
Light-Independent
Reactions
ATP, NADPH, CO2
Inputs
light, ADP,
NADP+, H2O
Produced
ATP, NADPH,
O2 , H +
glucose, ADP,
NADP+
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The End
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