PHOTOSYNTHESIS
Chapter 10
PHOTOSYNTHESIS
Overview: The Process That Feeds the BiospherePhotosynthesis
Is the process that converts light (sun) energy into chemical energy
Energy ConversionLight energy
ECOSYSTEM
CO2 + H2O
Photosynthesisin chloroplasts
Cellular respirationin mitochondria
Organicmolecules
+ O2
ATP
powers most cellular work
Heat
Summary Equation for Photosynthesis
6 CO2 + 12 H2O + Light energy C6H12O6 + 6 O2 + 6 H2 O
Photosynthesis is a redox process
Water is oxidized, carbon dioxide is reduced
It is an anabolic pathway with endergonic reactions
It requires energy
Summary Equation for Photosynthesis
Energy 6 CO2 6 H2O C6 H12 O6 6 O2
becomes reduced
becomes oxidized
Autotrophs vs. Heterotrophs
AutotrophsCan covert inorganic carbon sources to organic materialAre the producers of the biosphere
HeterotrophsObtain their organic material from other organismsAre the consumers of the biosphere
WHERE PHOTOSYNTHESIS OCCURS
The leaves of plantsAre the major sites of photosynthesis
Vein
Leaf cross section
Mesophyll
CO2 O2Stomata
STRUCTURE OF CHLOROPLASTS
Chloroplast
Mesophyll
5 µm
Outermembrane
IntermembranespaceInner
membrane
Thylakoidspace
ThylakoidGranumStroma
1 µm
The Nature of Sunlight
LightIs a form of electromagnetic energy, which travels in waves
WavelengthIs the distance between the crests of wavesDetermines the type of electromagnetic energy
The visible light spectrumIncludes the colors of light we can seeIncludes the wavelengths that drive photosynthesisIs in the 380 nm to 750 nm wavelength range
Gammarays X-rays UV Infrared
Micro-waves
Radiowaves
10–5 nm 10–3 nm 1 nm 103 nm 106 nm1 m
106 nm 103 m
380 450 500 550 600 650 700 750 nm
Visible light
Shorter wavelength
Higher energy
Longer wavelength
Lower energy
ELECTROMAGNETIC SPECTRUM
PHOTOSYNTHETIC PIGMENTS
Absorb light waves that are used in photosynthesis orReflect light waves that are not used in photosynthesis
LightReflectedLight
Chloroplast
Absorbedlight
GranumTransmitt
edlight
Green light is NOT used!
ABSORPTION SPECTRA
The three curves show the wavelengths of light best absorbed by three types of chloroplast pigments
.
Ab
sorp
tion
of
lig
ht
by
chlo
rop
last
pig
men
tsChlorophyl
l a
Wavelength of light (nm)
Chlorophyll b
Carotenoids
Photosynthesis consists of two processesLight reactions
Occur in the thylakoid membranesSplits waterReleases oxygenProduces ATP and NADPH
Calvin cycleOccurs in the stromaForms sugar from carbon dioxideUsing ATP (for energy) and NADPH (for reducing power) from the light reactions
STAGES OF PHOTOSYNTHESIS
Light
LightReactions
CalvinCycle
Chloroplast
[CH2O](sugar)
ATP
NADPH
NADP
ADP
+ P i
H2O CO2
O2
EXCITATION OF CHLOROPHYLL BY LIGHT
Excitedstate
En
erg
y of
ele
ctio
n
Heat
Photon(fluorescence)
Chlorophyllmolecule
GroundstatePhoton
e–
When a pigment absorbs lightIt goes from a ground state to an excited state, which is unstable
CHLOROPHYLL IN A PHOTOSYSTEM
A photosystemIs composed of a reaction center surrounded by a number of light-harvesting complexes
Thylakoid membranes are populated by two types of photosystems, I (P700) and II (P680)
Primary electionacceptor
Photon
Thylakoid
Light-harvestingcomplexes
Reactioncenter
Photosystem
STROMA
Th
yla
koid
m
em
bra
ne
Transferof energy
Specialchlorophyll amolecules
Pigmentmolecules
THYLAKOID SPACE(INTERIOR OF THYLAKOID)
e–
LIGHT REACTIONS ANAOLGY
Millmakes
ATP
ATP
e–
e–e–
e–
e–
Photo
n
Photosystem II Photosystem I
e–
e–
NADPH
Photo
n
Cytochromecomplex
Primaryacceptor
Primaryacceptor
H2O
O2
2 H
+1/2
P680
Light
Pigmentmolecules
Photosystem II(PS II)
Photosystem I(PS I)
Pq
Pc
ATP
1
2
3
5
6
7
8
Electron transport chain
Electron
transport
chain
P700
Light
+ HNADP
NADPH
NADP
reductase
Fd
e
e
e
e
4
e
e
LIGHT REACTIONSLINEAR (NON-CYCLIC)
ELECTRON FLOW
LIGHT REACTIONSCYCLIC ELECTRON FLOW
Primaryacceptor
Pq
Fd
Cytochromecomplex
Pc
Primaryacceptor
Fd
NADP+
reductaseNADPH
ATPPhotosystem II Photosystem I
NADP+
Occasionally, electrons take a different pathIn cyclic electron flow
Only photosystem I is usedOnly ATP is produced
Chemiosmosis and Photophosphorylation
STROMA(low H concentration)
STROMA(low H concentration)
THYLAKOID SPACE(high H concentration)
Light
Photosystem II
Cytochromecomplex Photosystem I
Light
NADP
reductase
NADP + H
ToCalvinCycle
ATPsynthase
Thylakoidmembrane
2
1
3
NADPH
Fd
Pc
Pq
4 H+
4 H++2 H+
H+
ADP+P i
ATP
1/2
H2OO2
CALVIN CYCLE
The Calvin cycle uses ATP and NADPH from light reactions to convert CO2 to sugar
Sometimes called “dark” reactions or light independent reactionsOccurs in the stroma
The Calvin cycle has 3 phases
1.Carbon fixation
2.Reduction
3.Regeneration of the CO2 acceptor
Input
3 (Entering oneat a time)
CO2
Phase 1: Carbon fixation
Rubisco
3 P P
P6
Short-livedintermediate
6
6 ADP
ATP
6 P P
CalvinCycle
6 NADPH
6 NADP
6 P i
6 P
Phase 2: Reduction
Glyceraldehyde 3-phosphate(G3P)
P5G3P
ATP
3 ADP
Phase 3:Regeneration ofthe CO2 acceptor(RuBP)
3 P PRibulose bisphosphate
(RuBP)
1 PG3P
(a sugar)Output
Glucose andother organiccompounds
3
Calvin Cycle
REVIEW OF PHOTOSYNTHESIS
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
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
O2
CO2H2O
Light
Light reaction Calvin cycle
NADP+
ADP
ATP
NADPH
+ P 1
RuBP
Amino acidsFatty acids
Starch(storage)
Glucose (export)
G3P
Photosystem IIElectron transport chain
Photosystem I
Chloroplast
Top Related