Photosynthesis

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Photosynthesis

• Chapter 10

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Photosynthesis
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(d) Cyanobacteria
40 µm
(a) Plants
(b) Multicellular alga
1 µm
(e) Purple sulfur bacteria
10 µm
(c) Unicellular eukaryotes
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Experimental history

• Jan Baptista van Helmont
• Plants made their own food
• Joseph Priestly
• Plants restored the air

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Experimental history

• Jan Ingenhousz
• Suns energy split CO2
• Carbon Oxygen
• Oxygen was released into air
• Carbon combined with water
• Make carbohydrates

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Experimental history

• Fredrick Forest Blackman
• 1. Initial light reactions are independent of
  temperature
• 2. Second set of dark reactions are independent
  of light
• Dependent on CO2 concentrations temperature
• Enzymes involved in light-independent reactions

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Experimental history

• C.B. van Neil
• Looked at light in photosynthesis
• Studied photosynthesis in Bacteria

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C.B. van Neil

• CO2 2H2S ? (CH2O) H2O 2S
• CO2 2H2A ? (CH2O) H2O A2
• CO2 2H2O ? (CH2O) H2O O2

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C.B. van Neil

• O2 produce from plant photosynthesis comes from
  splitting water
• Not carbon dioxide
• Carbon Fixation
• Uses electrons H from splitting water
• Reduces carbon dioxide into organic molecules
  (simple sugars).
• Light-independent reaction

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• CO2 2H2O ? (CH2O) H2O O2
• CO2 2H2O ? (CH2O) H2O O2

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Photosynthesis

• Organisms capture energy from sunlight
• Build food molecules
• Rich in chemical energy
• 6CO2 12H2O ?
• C6H12O6 6H2O 6O2

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Photosynthesis

• Captures only 1 of suns energy
• Provides energy for life
• Source of energy when life began

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Photosynthesis

• Photon
• Packets of energy
• UV light photons have greater energy than visible
  light
• UV light has shorter wavelengths

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Photosynthesis

• Visible light
• Purple shorter wavelengths
• More energetic photons
• Red longer wavelengths
• Less energetic photons

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Spectrum
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1 m
10-
10-
nm
nm
1 nm
nm
10
nm
10
(10
nm)
10
m
5
3
3
6
9
3
Micro- waves
Radio waves
Gamma rays
UV
Infrared
X-rays
Visible light
380
450
500
550
600
650
700
750
nm
Shorter wavelength
Longer wavelength
Lower energy
Higher energy
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Absorption Spectrums

• Photon of energy strikes a molecule
• Absorbed by the molecule or lost as heat
• Depends on energy in photon (wavelength)
• Depends on atoms available energy levels
• Specific for each molecule

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Leaf structure

• Stoma (Stomata) opening on leaf
• Exchange of gases.
• Chloroplasts
• Mesophyll layer of leaf

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Chloroplasts

• Thylakoids
• Internal membranes of chloroplasts
• Grana
• Stacks of thylakoids
• Chlorophyll
• Green pigment
• Captures light for photosynthesis
• Membranes of thylakoids

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Chloroplasts

• Stroma
• Semi-liquid substance
• Surrounds thylakoids
• Contain enzymes
• Make organic molecules from carbon dioxide

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Chloroplasts
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Fig. 10-3b
Chloroplast
Outer membrane
Thylakoid
Intermembrane space
Thylakoid space
Granum
Stroma
Inner membrane
1 µm
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Figure 10.4
Leaf cross section
Chloroplasts
Vein
Mesophyll
Stomata
CO2
O2
Chloroplast
Mesophyll cell
Outer membrane
Thylakoid
Intermembrane space
Thylakoid space
Stroma
Granum
20 µm
Inner membrane
1 µm
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Pigments

• Molecules
• Absorb energy in visible range
• Chlorophylls Carotenoids
• Chlorophyll a b
• Absorb photons in the blue-violet red light

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Pigments

• Chlorophyll a main pigment of photosynthesis
• Converts light energy to chemical energy
• Chlorophyll b carotenoids are accessory
  pigments
• Capture light energy at different wavelengths

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Pigments
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Pigments

• Chlorophyll b

Chlorophyll a
Carotenoids
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Chlorophyll structure

• Located in thylakoid membranes
• A porphyrin ring with a Mg in center
• Hydrocarbon tail
• Photons are absorbed by the ring
• Absorbs photons very effectively
• Excites electrons in the ring

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Chlorophyll structure
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  sentation\10_07LightAndPigments_A.html

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Carotenoids

• Two carbon rings attached by a carbon chain
• Not as efficient as the Chlorophylls
• Beta carotene (helps eyes)
• Found in carrots and yellow veggies

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Photosystem

• Cluster of photosynthetic pigments
• Membrane of thylakoids (surface)
• Each pigment captures light energy
• Photosystem then gathers energy
• Energy makes ATP NADPH

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Photosystems

• Chlorophyll a molecules
• Accessory pigments (chlorophyll b carotenoids)
• Associated proteins

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Photosystems

• Consists of 2 components
• 1. Antenna (light gathering) complex
• 2. Reaction center

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Photosystem

• 1. Antenna complex
• Gathers photons from sun
• Web of Chlorophyll a molecules
• Held by proteins in membrane
• Accessory pigments carotenoids
• Energy is passed along the pigments to reaction
  center

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Photosystems

• 2. Reaction centers
• 2 special chlorophyll a molecules
• Accept the energy
• Chlorophyll a than passes the energized electron
  to an acceptor
• Acceptor is reduced (quinone)

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Photosystem
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Fig. 10-12
STROMA
Photosystem
Photon
Primary electron acceptor
Light-harvesting complexes
Reaction-center complex
e
Thylakoid membrane
Pigment molecules
Special pair of chlorophyll a molecules
Transfer of energy
THYLAKOID SPACE (INTERIOR OF THYLAKOID)
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Photosystem
STROMA
Reaction- center complex
Light- harvesting complexes
Photon
Primary electron acceptor
Chlorophyll
STROMA
e-
Thylakoid membrane
Thylakoid membrane
Transfer of energy
Special pair of chloro- phyll a molecules
THYLA- KOIDSPACE
Pigment molecules
THYLAKOID SPACE (INTERIOR OF THYLAKOID)
Protein subunits
(a) How a photosystem harvests light
(b) Structure of a photosystem
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2 photosystems

• Photosystem I (older)
• Absorbs energy at 700 nm wavelength
• Generates NADPH
• Photosystem II (newer)
• Absorbs energy at 680 nm wavelength
• Splits water (releases oxygen)
• Generates ATP
• 2 systems work together to absorb more energy

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NADP

• Nicotinamide Adenine Dinucleotide Phosphate
• Coenzyme
• Electron carrier
• Reduced during light-dependent reactions
• Used later to reduce carbon
• Carbon dioxide forms organic molecules
• Photosynthesis is a redox reaction

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Photophosphorylation

• Addition of phosphate group to ADP
• Light energy

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Photosynthesis

• Occurs in 3 stages
• 1. Capturing energy from sun
• 2. Energy makes ATP
• Reducing power in NADPH
• 3. ATP NADPH
• Power synthesis of organic molecules

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Photosynthesis

• Light dependent reactions
• First 2 steps of photosynthesis
• Presence of light
• Light-independent reactions
• Formation of organic molecules
• Calvin cycle
• Can occur /- light

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Photosynthesis

• 1. Chloroplasts
• 2. Light-dependent reactions
• Suns energy makes NADPH ATP
• 3. Light-independent reactions
• ATP NADPH
• CO2 into organic molecules

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Fig. 10-5-4
H2O
CO2
Light
NADP
ADP
P

i
Calvin Cycle
Light Reactions
ATP
NADPH
Chloroplast
CH2O (sugar)
O2
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Photosynthesis (Process)

• Light dependent reactions
• Linear electron flow
• Energy transfer
• Thylakoid membranes

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Light dependent reactions

• Photosystem II (680 nm)
• Light is captured by pigments
• Excites an electron (unstable)
• Energy is transferred to reaction center (special
  chlorophyll)
• Passes excited electron to an acceptor molecule

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Light dependent reactions

• PS II is oxidized
• Water splits (enzyme)
• Water donates an electron to chlorophyll
• Reduces PS II
• Oxygen (O2) is released with 2 protons (H)

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Light dependent reactions

• Electron is transported to PS I (700 nm)
• Electron is passed along proteins in the membrane
  (ETC)
• Protons are transported across the membrane
• Protons flow back across the membrane through
  ATP synthase
• Generate ATP

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Light dependent reactions

• At the same time PS I received light energy
• Excites an electron
• Primary acceptor accepts the electron
• PS I is excited
• Electron from PS II is passed to PS I
• Reduces the PS I

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Light dependent reactions

• PS I excited electron is passed to a second ETC
• Ferredoxin protein
• NADP reductase catalyzes the transfer of the
  electron to NADP
• Makes NADPH

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Fig. 10-13-5
Electron transport chain
Primary acceptor
Primary acceptor
4
7
Electron transport chain
Fd
Pq
e
2
e
8
e
e
NADP H
H2O
Cytochrome complex
2 H
NADP reductase

3
NADPH
O2
1/2
Pc
e
e
P700
5
P680
Light
Light
1
6
6
ATP
Pigment molecules
Photosystem I (PS I)
Photosystem II (PS II)
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Fig. 10-UN1
H2O
CO2
Primary acceptor
Electron transport chain
Primary acceptor
Fd
Electron transport chain
NADP H
H2O
Pq
NADP reductase
O2
NADPH
Cytochrome complex
Pc
Photosystem I
ATP
Photosystem II
O2
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Enhancement effect
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Enhancement effect
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Fig. 10-17
STROMA (low H concentration)
Cytochrome complex
Photosystem I
Photosystem II
Light
4 H
NADP reductase
Light
3
Fd
NADP H
NADPH
Pq
Pc
e
2
e
H2O
O2
1/2
1
THYLAKOID SPACE (high H concentration)
4 H
2 H
To Calvin Cycle
Thylakoid membrane
ATP synthase
STROMA (low H concentration)
ADP
ATP
P
i
H
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Fig. 10-16
Mitochondrion
Chloroplast
CHLOROPLAST STRUCTURE
MITOCHONDRION STRUCTURE
H
Diffusion
Intermembrane space
Thylakoid space
Electron transport chain
Inner membrane
Thylakoid membrane
ATP synthase
Stroma
Matrix
Key
ADP P
i
ATP
Higher H
H
Lower H
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Photosystems

• Noncyclic photophosphorylation
• 2 systems work in series
• Produce NADPH ATP
• Replaces electrons from splitting water
• System II (splits water)works first then I (NADPH)

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Photosystems

• When more ATP is needed
• Plant changes direction
• Electron used to make NADPH in PS I is directed
  to make ATP

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Calvin Cycle

• Named for Melvin Calvin
• Cyclic because it regenerates its starting
  material
• C3 photosynthesis
• First organic compound has 3 carbons

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Calvin cycle

• Combines CO2 to make sugar
• Using energy from ATP
• Using reducing power from NADPH
• Occurs in stroma of chloroplast

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Calvin Cycle

• Consists of three parts
• 1. Fixation of carbon dioxide
• 2. Reduction-forms G3P (glyceraldehyde
  3-phosphate)
• 3. Regeneration of RuBP (ribulose 1, 5
  bisphosphate)

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Calvin Cycle

• 3 cycles
• 3 CO2 molecules
• 1 molecule of G3P
• 6 NADPH
• 9 ATP

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Fixation of carbon

• CO2 combines with
• Ribulose 1, 5 bisphosphate (RuBP)
• Temporary 6 carbon intermediate
• Splits-forms 2- three carbon molecules
• 3-phosphoglycerate (PGA)
• Large enzyme that catalyses reaction
• (Rubisco) Ribulose bisphosphate
  carboxylase/oxygenase

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Reduction

• Phosphate is added to 3-phosphoglycerate
• 1,3 Bisphosphoglycerate
• NADPH reduces the molecule
• Glyceraldehyde 3-phosphate (G3P)

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Regeneration

• 5 molecules of G3P are rearranged to make 3 RuBP
• Uses 3 more ATP

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Fig. 10-18-3
(Entering one at a time)
Input
3
CO2
Phase 1 Carbon fixation
Rubisco
3
P
P
Short-lived intermediate
6
P
3
P
P
Ribulose bisphosphate (RuBP)
3-Phosphoglycerate
ATP
6
6 ADP
3 ADP
Calvin Cycle
P
6
P
3
ATP
1,3-Bisphosphoglycerate
6
NADPH
Phase 3 Regeneration of the CO2 acceptor (RuBP)
6 NADP
P
6
i
P
5
G3P
P
6
Glyceraldehyde-3-phosphate (G3P)
Phase 2 Reduction
1
P
Glucose and other organic compounds
Output
G3P (a sugar)
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Fig. 10-UN2
3 CO2
Carbon fixation
3 ? 5C
6 ? 3C
Calvin Cycle
Regeneration of CO2 acceptor
5 ? 3C
Reduction
1 G3P (3C)
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Calvin Cycle

• 3 CO2 enter cycle combine with RuBP
• Generates 3 molecules more of RuBP one G3P
  (glyceraldehyde 3-phosphate)
• G3P can be made into glucose other sugars

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Calvin Cycle

• Enzyme mediated
• 5 of these enzymes need light to be more
  efficient
• Net reaction
• 3CO2 9 ATP 6NADPH ?
• G3P 8Pi 9ADP 6NADP

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G3P

• G3P
• Converted to fructose 6-phosphate (reverse of
  glycolysis)
• Made into sucrose
• Happens in cytoplasm
• Intense photosynthesis
• G3P levels rise so much some is converted to
  starch

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Fig. 10-21
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
Starch (storage)
NADPH
Chloroplast
O2
Sucrose (export)
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Summary

• Light reactions
• Thylakoids
• Use Suns energy
• Make ATP NADPH
• Split water make oxygen

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Summary

• Dark reactions
• Stroma
• Use ATP NADPH
• Make G3P
• Regenerate
• ADP, Inorganic P, and NADP

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O2
CO2
H2O
Sucrose (export)
Mesophyll cell
Chloroplast
H2O
CO2
Light
NADP
ADP
3-Phosphoglycerate

LIGHT REACTIONSPhotosystem II Electron
transport chain
CALVIN CYCLE
P
RuBP
i
ATP
G3P
Photosystem I Electron transport chain
NADPH
Starch (storage)
Sucrose (export)
O2
H2O
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MAKE CONNECTIONS
Movement Across Cell Membranes (Chapter 7)
Energy Transformations in the Cell Photosynthesis
and Cellular Respiration (Chapters 810)
Flow of Genetic Information in the Cell DNA ?
RNA ? Protein (Chapters 57)
The Working Cell
DNA
1
Nucleus
mRNA
Nuclear pore
2
Rough endoplasmic reticulum (ER)
Protein
Protein in vesicle
3
mRNA
Vacuole
Ribosome
4
Vesicle forming
Photosynthesis in chloroplast
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CO2
Golgi apparatus
H2O
Protein
ATP
Transport pump
Organic molecules
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Plasma membrane
ATP
5
Cellular respiration in mitochondrion
ATP
O2
ATP
9
Cell wall
O2
CO2
H2O
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Photorespiration

• Rubisco oxidizes RuBP (starting molecules of
  Calvin cycle)
• Oxygen is incorporated into RuBP
• Undergoes reactions that release CO2
• CO2 O2 compete for same sight on the enzyme
• Under conditions greater than the optimal 250C
  this process occurs more readily

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Photorespiration

• Hot
• Stoma in leaf close to avoid loosing water
• Carbon dioxide cannot come in
• Oxygen builds up inside
• Carbon dioxide is released
• G3P is not produced

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C4 Photosynthesis

• Process to avoid loosing carbon dioxide
• Plant fixes carbon dioxide into a 4 carbon
  molecule (oxaloacetate)
• PEP carboxylase (enzyme)
• Oxaloacetate is converted to malate
• Then taken to stroma for Calvin cycle
• Sugarcane and corn

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C4 leaf anatomy
The C4 pathway
Mesophyll cell
Mesophyll cell
Photo- synthetic cells of C4 plant leaf
CO2
PEP carboxylase
Bundle- sheath cell
Oxaloacetate (4C)
PEP (3C)
ADP
Vein (vascular tissue)
Malate (4C)
ATP
Pyruvate(3C)
CO2
Bundle- sheath cell
Stoma
Calvin Cycle
Sugar
Vascular tissue
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CAM

• Process to prevent loss of CO2
• Plants in dry hot regions (cacti)
• Reverse what most plants do
• Open stoma at night
• Allows CO2to come in water to leave
• Close them during the day.

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CAM

• Carbon fix CO2 at night into 4 carbon chains
  (organic acids)
• Use the Calvin cycle during the day.

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Fig. 10-20
Sugarcane
Pineapple
C4
CAM
CO2
CO2
Mesophyll cell
Night
CO2 incorporated into four-carbon organic
acids (carbon fixation)
1
Organic acid
Organic acid
Bundle- sheath cell
Day
CO2
CO2
Organic acids release CO2 to Calvin cycle
2
Calvin Cycle
Calvin Cycle
Sugar
Sugar
(a) Spatial separation of steps
(b) Temporal separation of steps
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