Download Document

Ch. 10
• Photosynthesis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Photosynthesis
• Energy flows into ecosystem as sunlight,
• Feeds the Biosphere
• Converts solar E
into chemical E
Light energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2 + H2O
Cellular respiration
in mitochondria
Organic
molecules + O2
ATP
powers most cellular work
Figure 9.2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Heat
energy
Energy Transformations
• Photoautotrophs (producers)
– Use E of sunlight to make organic molecules
from water and CO2
(a) Plants
(c) Unicellular protist 10 m
(e) Pruple sulfur
bacteria
Figure 10.2
(b) Multicellular algae
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(d) Cyanobacteria
40 m
1.5 m
• Photosynthesis converts light E to the chemical
E of food
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Heterotrophs
• Obtain organic material f/ other organisms
• Consumers of the biosphere
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chloroplasts: Site of Photosynthesis (plants)
• Leaf
Leaf cross section
Vein
Mesophyll
Stomata
Figure 10.3
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CO2
O2
Leaf Anatomy
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chloroplasts
• Chloroplast Structure
–
Contain grana which consisting of thylakoid stacks
Mesophyll
Chloroplast
5 µm
Outer
membrane
Stroma
ThylakoidThylakoid
Granum
space
Intermembrane
space
Inner
membrane
1 µm
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chloroplasts
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Photosynthesis summary reaction
6 CO2 + 12 H2O + Light energy  C6H12O6 + 6 O2 + 6 H2 O
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chloroplasts split water into
• H2 and O2, incorporating the e- of H2 into sugar
molecules
Reactants:
Products:
12 H2O
6 CO2
C6H12O6
Figure 10.4
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
6
H2O
6
O2
Photosynthesis as a Redox Process
• Water is oxidized, CO2 is reduced
• Protons and Electron are taken
from water and added to CO2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Two Stages of Photosynthesis: A Preview
• Light Reactions
– Occurs on thylakoid membranes
– Converts solar E to chemical E
• Dark Reaction (Calvin Cycle)
– Occurs in the stroma
– Forms sugar from carbon
dioxide, using ATP for energy
and NADPH for reducing power
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview of photosynthesis
H2O
CO2
Light
NADP 
ADP
+ P
LIGHT
REACTIONS
CALVIN
CYCLE
ATP
NADPH
Chloroplast
Figure 10.5
O2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
[CH2O]
(sugar)
Lets Talk about Light
• Form of electromagnetic E, travels in waves
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Wavelength (l)
• Distance between the crests of waves
• Determines the type of electromagnetic E
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Electromagnetic spectrum
Entire range of electromagnetic E, or radiation
10–5
nm
10–3
Gamma
rays
103
1 nm
nm
X-rays
106
nm
UV
Infrared
1m
106 nm
nm
Microwaves
103 m
Radio
waves
Visible light
380
450
500
550
Shorter wavelength
Higher energy
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
600
650
700
Longer wavelength
Lower energy
750 nm
• Visible light spectrum
– Colors of light we can see
– l’s that drive photosynthesis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Photosynthetic Pigments: The Light Receptors
• Substances that absorb visible light
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Pigments
Reflect light, which include the colors we see
Light
Reflected
Light
Chloroplast
Absorbed
light
Granum
Transmitted
light
Figure 10.7
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Transmitted vs. Absorbed Light
Refracting
prism
White
light
Chlorophyll
solution
Photoelectric
tube
Galvanometer
2
3
1
0
100
4
Slit moves to
pass light
of selected
wavelength
Green
light
The high transmittance
(low absorption)
reading indicates that
chlorophyll absorbs
very little green light.
0
Blue
light
Figure 10.8
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
100
The low transmittance
(high absorption) reading
chlorophyll absorbs most blue light.
Absorption spectra of 3 types of pigments
Chlorophyll a
Absorption of light by
chloroplast pigments
Chlorophyll b
Carotenoids
Wavelength of light (nm)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Action spectrum of a pigment
Rate of photosynthesis
(measured by O2 release)
• Effectiveness of different l 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.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
First demonstrated by Theodor W. Engelmann
Aerobic bacteria
Filament
of alga
400
500
600
700
(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.
Light in the violet-blue and red portions of the spectrum are most effective in
driving photosynthesis.
CONCLUSION
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chlorophylls: Photosynthetic Pigments
• Chlorophyll a
CH3
in chlorophyll a
CHO
in chlorophyll b
CH2
–
CH
Main photosynthetic pigment
C
H3C
• Chlorophyll b
–
C
N
N
N
C
C
C
H
N
CH2
H
H
C
C
C
C
C
O
O
O
CH2
C
H
C
CH3
C
C
CH2
C
C
Mg
C
Accessory pigment
C
C
H3C
C
C
C
C
H
CH3
H
CH3
Porphyrin ring:
Light-absorbing
“head” of molecule
note magnesium
atom at center
O
O
CH3
CH2
Hydrocarbon tail:
interacts with hydrophobic
regions of proteins inside
thylakoid membranes of
chloroplasts: H atoms not
shown
Figure 10.10
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Assesory proteins
• Other accessory pigments
– Absorb different ls of light and pass the E to
chlorophyll a
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Excitation of Chlorophyll by Light
• When a pigment absorbs light electrons go
from their ground state to an excited state
(unstable)
e–
Excited
state
Heat
Photon
(fluorescence)
Photon
Figure 10.11 A
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chlorophyll
molecule
Ground
state
Photosystems I and II
e–
ATP
e–
e–
NADPH
e–
e–
e–
Mill
makes
ATP
e–
Photosystem II
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Photosystem I
Starter Question
• Compare and contrast the electron transport
chain in cellular respiration with the light
reactions in photosynthesis. Be sure to indicate
similarities and differences
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Photosystem II and I: Site of Photophosphorylation
• Proton Motive Force? Non Cyclic Flow to Calvin Cycle
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chemiosmosis in Chloroplasts v. Mitochondria
• Spatial organization of chemiosmosis
Key
Higher [H+]
Lower [H+]
Chloroplast
Mitochondrion
MITOCHONDRION
STRUCTURE
CHLOROPLAST
STRUCTURE
H+
Intermembrance
space
Membrance
Diffusion
Thylakoid
space
Electron
transport
chain
ATP
Synthase
Matrix
Figure 10.16
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
ADP+
Stroma
P
H+
ATP
Light reactions and chemiosmosis: Cyclic Flow
NADPH and O2
Not produce.
Does not go to
Calvin Cycle
STROMA
(Low H+ concentration)
H2O
CO2
LIGHT
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTOR
ATP
NADPH
O2
[CH2O] (sugar)
Cytochrome
complex
Photosystem II
Photosystem I
NADP+
reductase
Light
2 H+
3
NADP+ + 2H+
Fd
NADPH
+ H+
Pq
Pc
2
H2O
THYLAKOID SPACE
(High H+ concentration)
1⁄
2
1
O2
+2 H+
2 H+
To
Calvin
cycle
STROMA
(Low H+ concentration)
Thylakoid
membrane
ATP
synthase
ADP
ATP
P
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
H+
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Calvin cycle
• Uses ATP and NADPH to convert CO2 to sugar
• Similar to the citric acid cycle
• Occurs in the stroma
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Calvin Cycle Happens in the Stroma
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The “Other” Calvin Cycle
• Calvin cycle
Light
H2O
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
6 P
P
1,3-Bisphoglycerate
6 NADPH
Phase 3:
Regeneration of
the CO2 acceptor5
(RuBP)
6 NADPH+
6 P
P
(G3P)
Glyceraldehyde-3-P
Can go to sugars, amino acids,
fatty acids
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
6
P
Glyceraldehyde-3-phosphate
(G3P)
1
P
G3P
(a sugar)
Output
Glucose and
other organic
compounds
Phase 2:
Reduction
• Alternative mechanisms of carbon fixation have
evolved in hot, arid climates
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• On hot, dry days, plants close their stomata
– Conserving water but limiting access to CO2
– Causing O2 to build up  photorespiration
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Photorespiration: An Evolutionary Relic?
Photosynthetic rate is reduced
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
C4 Plants (e.g. corn)
• Minimize photorespiration
– Incorporate CO2 into four carbon compounds
in mesophyll cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 4 carbon compounds in bundle sheath cells
 release CO2  CO2 Calvin cycle
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CAM Plants (e.g. pineapple)
• Open their stomata at night, CO2  organic
acids
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• During the day, stomata close
– CO2 is released from the organic acids for use
in the Calvin cycle
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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.
• Review
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
• Organic compounds produced by
photosynthesis
– Provide the E and building material for
ecosystems
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Extra stuff: Light energy causes the
removal of an electron from a molecule of
P680 that is part of Photosystem II. The
P680 requires an electron, which is taken
from a water molecule, breaking the water
into H+ ions and O-2 ions. These O-2 ions
combine to form the diatomic O2 that is
released.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings