Transcript Photosynthesis

Fig. 10-2
(a) Plants
(c) Unicellular protist
10 µm
(e) Purple sulfur
bacteria
(b) Multicellular alga
(d) Cyanobacteria
40 µm
1.5 µm
Fig. 10-3a
Leaf cross section
Vein
Mesophyll
Stomata
Chloroplast
CO2
O2
Mesophyll cell
5 µm
Fig. 10-3b
Chloroplast
Outer
membrane
Thylakoid
Stroma
Granum
Thylakoid
space
Intermembrane
space
Inner
membrane
1 µm
Fig. 10-4
Reactants:
Products:
6 CO2
C6H12O6
12 H2O
6 H2 O
6 O2
Fig. 10-7
Light
Reflected
light
Chloroplast
Absorbed
light
Granum
Transmitted
light
Fig. 10-6
10–5 nm 10–3 nm
103 nm
1 nm
Gamma
X-rays
rays
UV
106 nm
Infrared
1m
(109 nm)
Microwaves
103 m
Radio
waves
Visible light
380
450
500
Shorter wavelength
Higher energy
550
600
650
700
750 nm
Longer wavelength
Lower energy
Fig. 10-9
RESULTS
Chlorophyll a
Chlorophyll b
Carotenoids
(a) Absorption spectra
400
500
600
700
Wavelength of light (nm)
(b) Action spectrum
Aerobic bacteria
Filament
of alga
(c) Engelmann’s
experiment
400
500
600
700
Fig. 10-5-4
CO2
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
Calvin
Cycle
ATP
NADPH
Chloroplast
O2
[CH2O]
(sugar)
Fig. 10-11
Energy of electron
e–
Excited
state
Heat
Photon
(fluorescence)
Photon
Chlorophyll
molecule
Ground
state
(a) Excitation of isolated chlorophyll molecule
(b) Fluorescence
Fig. 10-12
Photosystem
STROMA
Light-harvesting Reaction-center
complex
complexes
Primary
electron
acceptor
Thylakoid membrane
Photon
e–
Transfer
of energy
Special pair of
chlorophyll a
molecules
Pigment
molecules
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)
Fig. 10-13-4
4
Primary
acceptor
1/
2
H+
2
+
O2
H2O
e–
2
Primary
acceptor
e–
Pq
Cytochrome
complex
3
Pc
e–
e–
P700
5
P680
Light
1 Light
6
ATP
Pigment
molecules
Photosystem II
(PS II)
Photosystem I
(PS I)
Fig. 10-13-5
4
Primary
acceptor
2
H+
+
1/ O
2
2
H2O
e–
2
Primary
acceptor
e–
Pq
Cytochrome
complex
7
Fd
e–
e–
8
NADP+
reductase
3
NADPH
Pc
e–
e–
P700
5
P680
Light
1 Light
6
ATP
Pigment
molecules
Photosystem II
(PS II)
NADP+
+ H+
Photosystem I
(PS I)
Fig. 10-14
e–
ATP
e–
e–
NADPH
e–
e–
e–
Mill
makes
ATP
e–
Photosystem II
Photosystem I
Fig. 10-16
Mitochondrion
Chloroplast
MITOCHONDRION
STRUCTURE
CHLOROPLAST
STRUCTURE
H+
Intermembrane
space
Inner
membrane
Diffusion
Electron
transport
chain
Thylakoid
space
Thylakoid
membrane
ATP
synthase
Stroma
Matrix
Key
ADP + P i
[H+]
Higher
Lower [H+]
H+
ATP
Fig. 10-17
STROMA
(low H+ concentration)
Cytochrome
Photosystem I
complex
Light
Photosystem II
4 H+
Light
Fd
NADP+
reductase
NADP+ + H+
NADPH
Pq
H2O
THYLAKOID SPACE
(high H+ concentration)
e–
1
e–
1/
Pc
2
2
3
O2
+2 H+
4 H+
To
Calvin
Cycle
Thylakoid
membrane
STROMA
(low H+ concentration)
ATP
synthase
ADP
+
Pi
ATP
H+
Fig. 10-18-3
Input 3
(Entering one
at a time)
CO2
Phase 1: Carbon fixation
Rubisco
3 P
Short-lived
intermediate
P
6
P
3-Phosphoglycerate
3P
P
Ribulose bisphosphate
(RuBP)
6
ATP
6 ADP
3 ADP
3
Calvin
Cycle
6 P
P
1,3-Bisphosphoglycerate
ATP
6 NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP+
6 Pi
P
5
G3P
6
P
Glyceraldehyde-3-phosphate
(G3P)
1
Output
P
G3P
(a sugar)
Glucose and
other organic
compounds
Phase 2:
Reduction
Photorespiration: An Evolutionary Relic?
• In most plants (C3 plants), initial fixation of
CO2, via rubisco, forms a three-carbon
compound
• In photorespiration, rubisco adds O2 instead
of CO2 in the Calvin cycle
• Photorespiration consumes O2 and organic fuel
and releases CO2 without producing ATP or
sugar
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Photorespiration may be an evolutionary relic
because rubisco first evolved at a time when
the atmosphere had far less O2 and more CO2
• Photorespiration limits damaging products of
light reactions that build up in the absence of
the Calvin cycle
• In many plants, photorespiration is a problem
because on a hot, dry day it can drain as much
as 50% of the carbon fixed by the Calvin cycle
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
C4 Plants
• C4 plants minimize the cost of photorespiration by
incorporating CO2 into four-carbon compounds in
mesophyll cells
• This step requires the enzyme PEP carboxylase
• PEP carboxylase has a higher affinity for CO2 than
rubisco does; it can fix CO2 even when CO2
concentrations are low
• These four-carbon compounds are exported to
bundle-sheath cells, where they release CO2 that
is then used in the Calvin cycle
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 10-19
The C4 pathway
C4 leaf anatomy
Mesophyll
cell
Mesophyll cell
CO2
PEP carboxylase
Photosynthetic
cells of C4
Bundleplant leaf
sheath
cell
Oxaloacetate (4C)
Vein
(vascular tissue)
PEP (3C)
ADP
Malate (4C)
Stoma
Bundlesheath
cell
ATP
Pyruvate (3C)
CO2
Calvin
Cycle
Sugar
Vascular
tissue
CAM Plants
• Some plants, including succulents, use
crassulacean acid metabolism (CAM) to fix
carbon
• CAM plants open their stomata at night,
incorporating CO2 into organic acids
• Stomata close during the day, and CO2 is
released from organic acids and used in the
Calvin cycle
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 10-20
Sugarcane
Pineapple
C4
CAM
CO2
Mesophyll
cell
Organic acid
Bundlesheath
cell
CO2
1 CO2 incorporated
into four-carbon Organic acid
organic acids
(carbon fixation)
CO2
Calvin
Cycle
CO2
2 Organic acids
release CO2 to
Calvin cycle
Night
Day
Calvin
Cycle
Sugar
Sugar
(a) Spatial separation of steps
(b) Temporal separation of steps
The Importance of Photosynthesis: A Review
• The energy entering chloroplasts as sunlight gets
stored as chemical energy in organic compounds
• Sugar made in the chloroplasts supplies chemical
energy and carbon skeletons to synthesize the
organic molecules of cells
• Plants store excess sugar as starch in structures
such as roots, tubers, seeds, and fruits
• In addition to food production, photosynthesis
produces the O2 in our atmosphere
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 10-21
H2O
CO2
Light
NADP+
ADP
+ P
i
Light
Reactions:
Photosystem II
Electron transport chain
Photosystem I
Electron transport chain
RuBP
ATP
NADPH
3-Phosphoglycerate
Calvin
Cycle
G3P
Starch
(storage)
Chloroplast
O2
Sucrose (export)
Fig. 10-UN1
H2O
CO2
Primary
acceptor
Primary
acceptor
H2O
O2
Fd
Pq
NADP+
reductase
Cytochrome
complex
Pc
ATP
Photosystem II
O2
Photosystem I
NADP+
+ H+
NADPH
Drought? …. Abscisic acid
•In preparation for winter, ABA is
produced in terminal buds, this slows
plant growth.
•ABA also inhibits the division of cells
adjusting to cold conditions in the
winter by suspending primary and
secondary growth.
•ABA then translocates to the leaves,
where it rapidly alters the osmotic
potential of stomatal guard cells,
causing them to shrink and stomata to
close.
•Reduces transpiration
Indian Pipe