Transcript video slide - Hialeah Senior High School

Chapter 10
Photosynthesis
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chloroplasts: The Sites of Photosynthesis in Plants
• The leaves of plants
– Are the major sites of photosynthesis
Leaf cross section
Vein
Mesophyll
Stomata
Figure 10.3
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CO2
O2
• Chloroplasts
–
Are the organelles in which photosynthesis occurs
–
Contain thylakoids and grana
Mesophyll
Chloroplast
5 µm
Outer
membrane
Stroma Granum
Thylakoid Thylakoid
space
Intermembrane
space
Inner
membrane
1 µm
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Tracking Atoms Through Photosynthesis:
Scientific Inquiry
• Photosynthesis is summarized as
6 CO2 + 12 H2O + Light energy  C6H12O6 + 6 O2 + 6 H2 O
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Photosynthesis as a Redox Process
• Photosynthesis is a redox process
– Water is oxidized, carbon dioxide is reduced
LEO says GER
Lose electrons = oxidized
Gain electrons = reduced
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• An overview of photosynthesis
H2O
CO2
Light
NADP 
ADP
+ P
LIGHT
REACTIONS
CALVIN
CYCLE
ATP
NADPH
Chloroplast
Figure 10.5
O2
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[CH2O]
(sugar)
• Concept 10.2: The light reactions convert solar
energy to the chemical energy of ATP and
NADPH
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• Wavelength
– Is the distance between the crests of waves
– Determines the type of electromagnetic energy
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• The electromagnetic spectrum
– Is the entire range of electromagnetic energy, or
radiation
10–5 nm
10–3 nm
Gamma
rays
X-rays
UV
1m
106 nm
106 nm
103 nm
1 nm
Infrared
Microwaves
103 m
Radio
waves
Visible light
380
450
500
550
Shorter wavelength
Figure 10.6
Higher energy
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600
650
700
Longer wavelength
Lower energy
750 nm
– Reflect light, which include the colors we see
Light
Reflected
Light
Chloroplast
Absorbed
light
Granum
Transmitted
light
Figure 10.7
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• An absorption spectrum
– Is a graph plotting light absorption versus wavelength
Refracting Chlorophyll
prism
solution
White
light
2
Photoelectric
tube
Galvanometer
3
1
0
100
4
Slit moves to Green
pass light
light
of selected
wavelength
The high transmittance
(low absorption)
reading indicates that
chlorophyll absorbs
very little green light.
0
Figure 10.8
Blue
light
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100
The low transmittance
(high absorption) reading
chlorophyll absorbs most blue light.
• The absorption spectra of three types of pigments
in chloroplasts
Three different experiments helped reveal which wavelengths of light are photosynthetically
important. The results are shown below.
EXPERIMENT
RESULTS
Absorption of light by
chloroplast pigments
Chlorophyll a
Chlorophyll b
Carotenoids
Wavelength of light (nm)
(a) Absorption spectra. The three curves show the wavelengths of light best absorbed by
three types of chloroplast pigments.
Figure 10.9
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• The action spectrum of a pigment
Rate of photosynthesis
(measured by O2 release)
– Profiles the relative effectiveness of different
wavelengths of radiation in driving photosynthesis
(b) Action spectrum. This graph plots the rate of photosynthesis versus wavelength.
The resulting action spectrum resembles the absorption spectrum for chlorophyll
a but does not match exactly (see part a). This is partly due to the absorption of light
by accessory pigments such as chlorophyll b and carotenoids.
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• The action spectrum for photosynthesis
– Was first demonstrated by Theodor W. Engelmann
Aerobic bacteria
Filament
of alga
500
600
700
400
(c) Engelmann‘s experiment. In 1883, Theodor W. Engelmann illuminated a filamentous alga with light that had
been passed through a prism, exposing different segments of the alga to different wavelengths. He used aerobic
bacteria, which concentrate near an oxygen source, to determine which segments of the alga were releasing the
most O2 and thus photosynthesizing most.
Bacteria congregated in greatest numbers around the parts of the alga illuminated with violet-blue or red light.
Notice the close match of the bacterial distribution to the action spectrum in part b.
CONCLUSION
Light in the violet-blue and red portions of the spectrum are most effective in driving
photosynthesis.
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• The light reactions and chemiosmosis: the
organization of the thylakoid membrane
H2O
CO2
LIGHT
NADP+
ADP
LIGHT
REACTOR
CALVIN
CYCLE
ATP
NADPH
STROMA
(Low H+ concentration)
O2
[CH2O] (sugar)
Cytochrome
Photosystem II
complex
Photosystem I
NADP+
reductase
Light
2 H+
Fd
3
NADP+ + 2H+
NADPH + H+
Pq
Pc
2
H2O
THYLAKOID SPACE
1
(High H+ concentration)
1⁄
2
O2
+2 H+
2 H+
To
Calvin
cycle
STROMA
(Low H+ concentration)
Thylakoid
membrane
ATP
synthase
ADP
ATP
P
Figure 10.17
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H+
• Concept 10.3: The Calvin cycle uses ATP and
NADPH to convert CO2 to sugar
• The Calvin cycle
– Is similar to the citric acid cycle
– Occurs in the stroma
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• The Calvin cycle has three phases
– Carbon fixation
– Reduction
– Regeneration of the CO2 acceptor
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• The Calvin cycle
Light
H2 O
CO2
Input
3 (Entering one
CO2 at a time)
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTION
ATP
Phase 1: Carbon fixation
NADPH
O2
Rubisco
[CH2O] (sugar)
3 P
3 P
P
Short-lived
intermediate
P
Ribulose bisphosphate
(RuBP)
P
6
3-Phosphoglycerate
6
ATP
6 ADP
CALVIN
CYCLE
3 ADP
3
ATP
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 P
P
1,3-Bisphoglycerate
6 NADPH
6 NADPH+
6 P
P
5
(G3P)
6
P
Glyceraldehyde-3-phosphate
(G3P)
P
1
Figure 10.18
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G3P
(a sugar)
Output
Glucose and
other organic
compounds
Phase 2:
Reduction
• Concept 10.4: Alternative mechanisms of
carbon fixation have evolved in hot, arid
climates
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• On hot, dry days, plants close their stomata
– Conserving water but limiting access to CO2
– Causing oxygen to build up
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Photorespiration: An Evolutionary Relic?
• In photorespiration
– O2 substitutes for CO2 in the active site of the
enzyme rubisco
– The photosynthetic rate is reduced
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C4 Plants
• C4 plants minimize the cost of photorespiration
– By incorporating CO2 into four carbon
compounds in mesophyll cells
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• These four carbon compounds
– Are exported to bundle sheath cells, where
they release CO2 used in the Calvin cycle
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• C4 leaf anatomy and the C4 pathway
Mesophyll
cell
Mesophyll cell
Photosynthetic
cells of C4 plant
leaf
CO
CO
2 2
PEP carboxylase
Bundlesheath
cell
PEP (3 C)
ADP
Oxaloacetate (4 C)
Vein
(vascular tissue)
Malate (4 C)
ATP
C4 leaf anatomy
BundleSheath
cell
Pyruate (3 C)
CO2
Stoma
CALVIN
CYCLE
Sugar
Vascular
tissue
Figure 10.19
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CAM Plants
• CAM plants
– Open their stomata at night, incorporating CO2
into organic acids
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• During the day, the stomata close
– And the CO2 is released from the organic acids
for use in the Calvin cycle
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• The CAM pathway is similar to the C4 pathway
Pineapple
Sugarcane
C4
Mesophyll Cell
Organic acid
Bundlesheath
cell
(a) Spatial separation
of steps. In C4
plants, carbon fixation
and the Calvin cycle
occur in different
Figure 10.20 types of cells.
CAM
CO2
CALVIN
CYCLE
CO2
1 CO2 incorporated Organic acid
into four-carbon
organic acids
(carbon fixation)
2 Organic acids
release CO2 to
Calvin cycle
Sugar
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CALVIN
CYCLE
Sugar
Night
Day
(b) Temporal separation
of steps. In CAM
plants, carbon fixation
and the Calvin cycle
occur in the same cells
at different times.
The Importance of Photosynthesis: A Review
• A review of photosynthesis
Light reaction
Calvin cycle
H2O
CO2
Light
NADP+
ADP
+P1
RuBP
3-Phosphoglycerate
Photosystem II
Electron transport chain
Photosystem I
ATP
NADPH
G3P
Starch
(storage)
Amino acids
Fatty acids
Chloroplast
Figure 10.21
O2
Light reactions:
• Are carried out by molecules in the
thylakoid membranes
• Convert light energy to the chemical
energy of ATP and NADPH
• Split H2O and release O2 to the
atmosphere
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Sucrose (export)
Calvin cycle reactions:
• Take place in the stroma
• Use ATP and NADPH to convert
CO2 to the sugar G3P
• Return ADP, inorganic phosphate,
and
NADP+ to the light reactions