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Photosynthesis
Photosynthesis
Chapter 9Chapter 9
Plant Kingdom
Plant Kingdom
- produce most of the food in the biosphere
- Autotrophs: make their own food- Heterotrophs: obtain food from
other organisms- Plants are photoautotrophs:
convert light energy into chemical energy (food: glucose) using CO2 and H2O
(a) Plants
(b) Multicellular algae
(c) Unicellular protist 10 m
40 m(d) Cyanobacteria
1.5 m(e) Purple sulfurbacteria
Photoautotrophs
Photoautotrophs
I. ChloroplastsI. Chloroplasts- site of photosynthesis in plantsA. Leaf
- main photosynthetic surface 1. Mesophyll
- middle tissue layer of leaf that contains chloroplasts
2. Stomata- pores in leaf that let in CO2
3. Vein- supply water
Guardcells
Stomatal pore
Epidermalcell
Surface view of a spiderwort(Tradescantia) leaf (LM)
(b)Stoma
Upperepidermis
Palisademesophyll
Spongymesophyll
Lowerepidermis
Vein
Guard cells
Xylem
Phloem
Guard cells
Cutaway drawing of leaf tissues(a)
Vein Air spaces Guard cells
Transverse section of a lilac(Syringa) leaf (LM)
(c)
Leaf Structure
Leaf Structure
B.Structure of Chloroplasts
B.Structure of Chloroplasts
- 30-40/plant cell- probably evolved from free-living
cyanobacteria
1. Stroma- fluid within chloroplast
2. Thylakoids- interconnected, membranous sacs- stacked into grana- chlorophyll attached to membrane
Location of Photosynthesis in a Plant
Location of Photosynthesis in a Plant
Mesophyll cell
Mesophyll
Vein
Stomata
CO2 O2
Chloroplast
5 µm
1 µm
Outermembrane
Intermembranespace
Inner membrane
Thylakoid ThylakoidSpace
GranumStroma
Leaf cross section
A.Light Energy A.Light Energy - visible light only a small part of
the electromagnetic spectrum
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
B. Photosynthetic Pigments
B. Photosynthetic Pigments
- Pigments are substances that absorb light energy
- Plants appear green because chlorophyll reflects green light
- Chlorophyll absorbs violet-blue and red light
LightReflectedLight
Chloroplast
Absorbed light
Granum
Transmittedlight
Why Leaves Are Green: Interaction of Light with Chloroplasts
Why Leaves Are Green: Interaction of Light with Chloroplasts
1.Absorption Spectrum 1.Absorption Spectrum - shows wavelengths absorbed
by chlorophyll
Ab
sorp
tio
n o
f li
gh
t b
ych
loro
pla
st p
igm
ents
400 500 600 700
Chlorophyll a
Chlorophyll b
Carotenoids
Wavelength of light (nm)
II. Photosynthesis
Overview II. Photosynthesis
Overview
6CO2 + 6H2O C6H12O6 + 6O2 Reactants Products
- not a single reaction, but a series of complex reactions in 2 main stages:
A. Light – Dependent Reaction
A. Light – Dependent Reaction
1. Light hits a chlorophyll molecule causing the electrons to move to a higher energy level.
2. This starts a series of reactions that converts light energy into ATP, which is the chemical energy source used in cells.
Light Dependent reactionLight Dependent reaction-This phase of photosynthesis
needs water also-enzymes remove electrons from
water and split oxygen and hydrogen.
-Oxygen is given off as by product.
-Hydrogen used to make sugars.
Main Point of Light Reaction:
Main Point of Light Reaction:
- Light energy is used to produce ATP which is used in the Calvin Cycle to make sugar.
- Light energy is converted to chemical energy.
B.Calvin Cycle or Light Independent reaction
B.Calvin Cycle or Light Independent reaction
- occurs in the stroma
- Needs ATP produced by Light dependent reaction
- Carbon from carbon dioxide molecules combine with hydrogen to form sugars, a form of chemical energy
Calvin CycleCalvin Cycle- sugar factory in chloroplast
- takes CO2 with ATP from the light reaction to make sugar
- actual product is Glyceraldehyde-3-phosphate (G3P), a 3-C sugar which then turns into glucose, a 6 carbon sugar.
CO2
CALVINCYCLE
O2
[CH2O](sugar)
NADP
ADP+ P i
H2O
Light
LIGHT REACTIONS
Chloroplast
ATP
NADPH
An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
Think Pair ShareThink Pair ShareWhat does the Calvin cycle need
from the light reaction before it will work?
Why would you be dead if not for the Calvin cycle?
Structure of Chlorophyll Molecules in Chloroplasts of
Plants
Structure of Chlorophyll Molecules in Chloroplasts of
Plants
C
CH
CH2
CC
CC
C
CNNC
H3C
C
CC
C C
C
C
C
N
CC
C
C N
MgH
H3C
H
C CH2CH3
H
CH3C
HHCH2
CH2
CH2
H CH3
C O
O
O
O
O
CH3
CH3
CHO
in chlorophyll a
in chlorophyll b
Porphyrin ring:Light-absorbing“head” of molecule;note magnesiumatom at center
Hydrocarbon tail:interacts with hydrophobicregions of proteins insidethylakoid membranes ofchloroplasts: H atoms notshown
1. Photon of light strikes a pigment molecule and energy is transferred through several pigment molecules.
1. Photon of light strikes a pigment molecule and energy is transferred through several pigment molecules.
e–
Primary electionacceptor
Photon
Thylakoid
Light-harvestingcomplexes
Reactioncenter
PhotosystemSTROMA
Th
ylak
oid
mem
bra
ne
Transferof energy Special
chlorophyll amolecules
Pigmentmolecules
THYLAKOID SPACE(INTERIOR OF THYLAKOID)
2. Energy is then funneled to Chlorophyll a (P680) in the reaction center of PS II.
2. Energy is then funneled to Chlorophyll a (P680) in the reaction center of PS II.
H2O CO2
Light
LIGHT REACTIONS
CALVIN CYCLE
O2
NADP+
ADP
ATP
NADPH
[CH2O] (sugar)
Light
Photosystem II (PS II)
e
Primary acceptor
P6801
2
En
erg
y o
f el
ectr
on
s
3. Electron from “excited” Chlorophyll a is captured by Primary Acceptor Molecule.
3. Electron from “excited” Chlorophyll a is captured by Primary Acceptor Molecule.
H2O CO2
Light
LIGHT REACTIONS
CALVIN CYCLE
O2
NADP+
ADP
ATP
NADPH
[CH2O] (sugar)
Light
Photosystem II (PS II)
e
Primary acceptor
P6801
2
En
erg
y o
f el
ectr
on
s
4.An enzyme splits a H2O into 2 electrons, 2 H+ ions, and 1 Oxygen atom (O2 released).
4.An enzyme splits a H2O into 2 electrons, 2 H+ ions, and 1 Oxygen atom (O2 released).
H2O CO2
Light
LIGHT REACTIONS
CALVIN CYCLE
O2
NADP+
NADPH
[CH2O] (sugar)
Light
Photosystem II (PS II)
e
Primary acceptor
ADP
ATP
2 H+
+
O21⁄2
H2O
e
e
1
3
2
En
erg
y o
f el
ectr
on
s
P680
5. The electron from water replaces the “excited” electron lost by Chlorophyll a.
5. The electron from water replaces the “excited” electron lost by Chlorophyll a.
H2O CO2
Light
LIGHT REACTIONS
CALVIN CYCLE
O2
NADP+
NADPH
[CH2O] (sugar)
Light
Photosystem II (PS II)
e
Primary acceptor
ADP
ATP
2 H+
+
O21⁄2
H2O
e
e
1
3
2
En
erg
y o
f el
ectr
on
s
P680
6. As the “excited” electron falls back to its “normal” state, energy is harnessed to form ATP.
6. As the “excited” electron falls back to its “normal” state, energy is harnessed to form ATP.
1
3O2
+
H2O CO2
Light
LIGHT REACTIONS
CALVIN CYCLE
O2
NADP+
NADPH
[CH2O] (sugar)
Light
Photosystem II (PS II)
e
Primary acceptor
ATP
2 H+
1⁄2
H2O2
En
erg
y o
f el
ectr
on
s
ADP
Pq
Cytochromecomplex
Pc
ATP
Electron transport chain
5
4
P680
e
e
7. Light energy also excites an electron of Chlorophyll a (P700) in Photosystem I.
7. Light energy also excites an electron of Chlorophyll a (P700) in Photosystem I.
O2
H2O CO2
Light
LIGHT REACTIONS
CALVIN CYCLE
O2
NADPH
[CH2O] (sugar)
Light
Photosystem II (PS II)
e
Primary acceptor
2 H+
1⁄2
H2O2
En
erg
y o
f el
ectr
on
s
ADP
Pq
Cytochromecomplex
Pc
ATP
Electron transport chain
5
NADP+
ATP
Primary acceptor
e
Photosystem I (PS I)
Light
6
1
3
4
P680
P700
+
e
e
7. The Primary Acceptor Molecule of PS I captures that excited electron (replaced by the “spent” electron from the electron transport chain).
7. The Primary Acceptor Molecule of PS I captures that excited electron (replaced by the “spent” electron from the electron transport chain).
O2
H2O CO2
Light
LIGHT REACTIONS
CALVIN CYCLE
O2
NADPH
[CH2O] (sugar)
Light
Photosystem II (PS II)
e
Primary acceptor
2 H+
1⁄2
H2O2
En
erg
y o
f el
ectr
on
s
ADP
Pq
Cytochromecomplex
Pc
ATP
Electron transport chain
5
NADP+
ATP
Primary acceptor
e
Photosystem I (PS I)
Light
6
1
3
4
P680
P700
+
e
e
8. The excited electron of PS I passes through a shorter electron transport chain to NADP+ reducing it to NADPH.
8. The excited electron of PS I passes through a shorter electron transport chain to NADP+ reducing it to NADPH.
P700
+
CO2
Photosystem II (PS II)
H2O
Light
LIGHT REACTIONS
CALVIN CYCLE
O2
NADPH
[CH2O] (sugar)
e
Primary acceptor
2 H+
1⁄2
H2O
e
e
1
En
erg
y o
f el
ectr
on
s
Pq
Cytochromecomplex
Pc
ATP
Electron transport chain
NADP+
Primary acceptor
e
Photosystem I (PS I)
Light
66
2
Light
ADP
ATP
5
Fd
ElectronTransportchain
7
NADP+
reductaseNADPH
NADP+
+ 2 H+
8
+ H+
1
3
4
P680
O2
e
e
A mechanical analogy for the light reactions
A mechanical analogy for the light reactions
Millmakes
ATP
ATP
e–
e–e–
e–
e–
Ph
oto
n
Photosystem II Photosystem I
e–
e–
NADPH
Ph
oto
n
The Light Reactions and Chemiosmosis: The Organization of the Thylakoid
Membrane
The Light Reactions and Chemiosmosis: The Organization of the Thylakoid
Membrane
LIGHTREACTOR
NADP+
ADP
ATP
NADPH
CALVINCYCLE
[CH2O] (sugar)STROMA(Low H+ concentration)
Photosystem II
LIGHT
H2O CO2
Cytochromecomplex
O2
H2OO2
1
1⁄2
2
Photosystem ILight
THYLAKOID SPACE(High H+ concentration)
STROMA(Low H+ concentration)
Thylakoidmembrane
ATPsynthase
PqPc
Fd
NADP+
reductase
NADPH + H+
NADP+ + 2H+
ToCalvincycle
ADP
PATP
3
H+
2 H++2 H+
2 H+
ATP Synthase, a Molecular Mill
ATP Synthase, a Molecular Mill
STROMA
THYLAKOID SPACE
H+
H+
H+
H+
H+
H+ H+
H+
P i
+
ADP
ATP
A rotor within the membrane spins clockwise whenH+ flows pastit down the H+
gradient.
A stator anchoredin the membraneholds the knobstationary.
A rod (or “stalk”)extending into the knob alsospins, activatingcatalytic sites inthe knob.
Three catalytic sites in the stationary knobjoin inorganic Phosphate to ADPto make ATP.
Comparison of chemiosmosis in mitochondria and
chloroplasts
Comparison of chemiosmosis in mitochondria and
chloroplastsKey
Higher [H+]
Lower [H+]
Mitochondrion Chloroplast
MITOCHONDRIONSTRUCTURE
Intermembrancespace
Membrance
Matrix
Electrontransport
chain
H+ DiffusionThylakoidspace
Stroma
ATPH+
PADP+
ATPSynthase
CHLOROPLASTSTRUCTURE
A. Carbon Fixation A. Carbon Fixation - CO2 attached to Ribulose
Bisphosphate (RuBP), a 5-C sugar
- The 6-C unstable intermediate molecule breaks down to 2 molecules of 3-Phosphoglycerate
The Calvin Cycle
The Calvin Cycle
LightH2O CO2
LIGHTREACTIONS
ATP
NADPH
NADP+
[CH2O] (sugar)
CALVINCYCLE
ADP
(Entering oneat a time)CO2
3
Phase 1: Carbon fixation
Rubisco
Short-livedintermediate
3 P P
3 P P
Ribulose bisphosphate(RuBP)
P
3-Phosphoglycerate6 ATP
6 ADP
Input
CALVINCYCLE
O2
6
B. Reduction B. Reduction - each 3-Phosphoglycerate gets a
phosphate from ATP to form 1,3-Bisphosphoglycerate
- 2 electrons from NADPH reduces 1,3-Bisphosphoglycerate to G3P
- one G3P molecule (out of every 6) is released: 2 G3P’s = 1 glucose
The Calvin Cycle
The Calvin Cycle
(Entering oneat a time)CO2
3
Phase 1: Carbon fixation
Rubisco
Short-livedintermediate
3 P P
3 P P
Ribulose bisphosphate(RuBP)
P
3-Phosphoglycerate
P6 P
1,3-Bisphosphoglycerate
6 NADPH
6 NADP+
6 P i
P6
Glyceraldehyde-3-phosphate(G3P)
Phase 2:Reduction
6 ATP
CALVINCYCLE
P1
G3P(a sugar)Output
Glucose andother organiccompounds
6 ADP
InputLightH2O CO2
LIGHTREACTIONS
ATP
NADP+
[CH2O] (sugar)
CALVINCYCLE
NADPH
ADP
O2
6
C. Regeneration of RuBP C. Regeneration of RuBP - 5 G3P molecules are used to
make 3 RuBP molecules
- uses 3 ATP’s
- cycle continues
For each G3P molecule produced, 9 ATP’s and 6 NADPH’s used
The Calvin cycle
The Calvin cycle
(Entering oneat a time)CO2
3
Phase 1: Carbon fixation
Rubisco
Short-livedintermediate
3 P P
3 P P
Ribulose bisphosphate(RuBP)
P
3-Phosphoglycerate
P6 P
1,3-Bisphosphoglycerate
6 NADPH
6 NADP+
6 P i
P6
Glyceraldehyde-3-phosphate(G3P)
Phase 2:Reduction
6 ATP
3 ATP
3 ADP CALVINCYCLE
P5
Phase 3:Regeneration ofthe CO2 acceptor(RuBP)
P1
G3P(a sugar)Output
Glucose andother organiccompounds
G3P
6 ADP
LightH2O CO2
LIGHTREACTIONS
NADPH
NADP+
[CH2O] (sugar)
CALVINCYCLE
Input
ATP
ADP
O2
6
A Review of PhotosynthesisA 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 reactions Calvin cycle
NADP+
ADP
ATP
NADPH
+ P 1
RuBP 3-Phosphoglycerate
Amino acidsFatty acids
Starch(storage)
Sucrose (export)
G3P
Photosystem IIElectron transport chain
Photosystem I
Chloroplast
V.Cyclic Electron FlowV.Cyclic Electron Flow- an alternate, “short circuit”, path
involving only PS I
- electron from Primary Electron Acceptor passes to Ferredoxin and then to Cytochrome Complex (electron transport chain)
- ATP produced but no NADPH
V.Cyclic Electron FlowV.Cyclic Electron Flow
Primaryacceptor
Pq
Fd
Cytochromecomplex
Pc
Primaryacceptor
Fd
NADP+
reductase
NADPH
ATPPhotosystem II(PS II)
Photosystem I(PS I)
NADP+
Why? Why? - Noncyclic Electron Flow produces
ATP and NADPH in equal amounts but Calvin Cycle uses more ATP than NADPH
- Accumulated NADPH seems to cause a shift to Cyclic Electron Flow to correct the imbalance
VI. PhotorespirationVI. Photorespiration- C3 plants include 85% of all plants
- have a built-in inefficiency
- on hot, sunny days stomates close to conserve water
- closed stomates prevent CO2 from entering leaf
- O2 concentration in leaf increases while CO2 decreases
- Rubisco binds O2 to ribulose bisphosphate (instead of CO2) which splits forming a 2-carbon compound which is released as CO2
- Photo (light) & respiration (consumes O2 and produces CO2)
- Uses up ATP (rather than producing ATP)
~ 50% of fixed carbon lost from Calvin Cycle by photorespiration
- reduces photosynthetic output and crop yield
VII. C4 PlantsVII. C4 Plants- found in corn, sugarcane,
crabgrass, etc.
- an adaptation to hot, dry climate (avoids the problem of photorespiration)
- involves unique leaf anatomy
VII. C4 PlantsVII. C4 Plants
CorCornn
Sugar Sugar CaneCane
The
The
EndEnd
Photosynthesis Animation
Photosynthesis Animation
