photosynthesis. light energy photosynthesis 6 co 2 6+ h2oh2o carbon dioxidewater c 6 h 12 o 6 6+...
TRANSCRIPT
Photosynthesis
Lightenergy
PHOTOSYNTHESIS
6 CO2 6+ H2O
Carbon dioxide Water
C6H12O6 6+ O2
Glucose Oxygen gas
Photosynthesis
– Human demand for energy • Fossil fuel supplies?
– Energy plantations• Biomass energy
• Photoautotrophs
– C source?
– Energy source?
• Heterotrophs
– C source?
– Energy source?
Carbon and Energy
Photoautotrophs
Figure 7.1A–D
•Green parts…– Chloroplasts (stroma and thylakoids)
– Stomata
Leaf Cross Section
Leaf
Mesophyll Cell
Mesophyll
VeinStoma
CO2O2
Chloroplast
Chloroplast
Grana Stroma
TE
M 9
,750
Stroma
Granum Thylakoid Thylakoidspace
OutermembraneInnermembrane
Intermembranespace
LM 2
,600
Where does PS happen?
• By splitting water
Where does O2 come from?
•Redox processes
Reduction
Oxidation
6 O2 6 H2O
Reduction
Oxidation
6 O26 CO2 6 H2O C6H12O6
C6H12O6 6 CO2
Just like respiration?
Linked Processes
Photosynthesis
• Energy-storing
• Releases O2
• Requires CO2
Aerobic Respiration
• Energy-releasing
• Requires O2
• Releases CO2
2 stages•The light reactions…– Energy capture
– produce O2
•The Calvin cycle– Uses CO2
– Makes sugar
•The Coenzymes– ATP
– NADPH
Overview
Light
CO2H2OChloroplast
LIGHTREACTIONS(in thylakoids)
CALVINCYCLE
(in stroma)
NADP+
ADP+ P
ATP
NADPH
O Sugar
Electrons
Visible LightIncreasing energy
10–5 nm 10–3 nm 1 nm 103 nm 106 nm 1 m 103 m
Gammarays
X-rays UV Infrared Micro-waves
Radiowaves
Visible light
400 500 600 700 750
650nm
Wavelength (nm)
Transmittedlight
Absorbedlight
Reflectedlight
Light
Chloroplast
380
Pigments
Colors?
• Wavelengths not absorbed
• Chlorophylls a and b
• Carotenoids
ChlorophyllsW
avel
eng
th a
bso
rpti
on
(%
)
Wavelength (nanometers)
chlorophyll b
chlorophyll a
T.E. Englemann’s Experiment
Photons
• Packets of light energy
• Shortest wavelength (blue-violet light) = highest energy
Strike chlorophyll in photosystemExcite an electron
Figure 7.7B, C
Ene
rgy
of e
lect
ron
Photon
Excited state
Heat
Photon(fluorescence)
Ground state
Chlorophyllmolecule
e–
Photosystem
Light-harvestingcomplexes
Reactioncenter
Primary electronacceptor
e–
To electrontransport chain
Pigment molecules
Chlorophyll a moleculeTransfer of energy
Photon
Thy
lako
id m
embr
ane
Photons and Photosystems
• Photon energy transfer to reaction-center
• Excites electron• Which is taken by the primary
electron acceptor• Which leads to the ETC
Ene
rgy
of e
lect
ron
Photon
Excited state
Heat
Photon(fluorescence)
Ground state
Chlorophyllmolecule
e–
Photosystem
Light-harvestingcomplexes
Reactioncenter
Primary electronacceptor
e–
To electrontransport chain
Pigment molecules
Chlorophyll a moleculeTransfer of energy
PhotonT
hyla
koid
mem
bran
e
Photosystem: Harvester Pigments
• When excited by light energy:
Electron Transfer Chain• Uses electrons from reaction
center• Powers H+ pump to produce ATP • Produces NADPH
Thylakoidspace
Photon
Stroma
Th
yla
koid
me
mb
ran
e
1
Photosystem II
e–
P680
2
H2O 12
+ 2O2 H+
3
ATPElectron transport chainProvides energy for synthesis of
by chemiosmosis
4
Photosystem I
Photon
P700
e–
5
+NADP+ H+ NADPH
6
– Electrons move from photosystem II to I• Make ATP
– Electrons from photosystem I• Reduce NADP+ to NADPH
Figure 7.8B
e–
ATP
MillmakesATP
Pho
ton
Pho
ton
Photosystem II Photosystem I
NADPHe–
e–e–
e–
e–
e–
Electron Transfer Chain
ATP ProductionChloroplast
Stroma (low H+ concentration)
Light Light
NADP+ + H+ NADPH
H+
H+
H+
H+
ATPPADP +
Thylakoidmembrane
H2O 1
2O2 2 H+ H+
H+
H+ H+
H+
H+
H+ H+
H+
H+
Photosystem II Electrontransport chain
Photosystem I ATP synthase
Thylakoid space(high H+ concentration)
+
• They put the “synthesis” in
photosynthesis
• Calvin-Benson cycle
• In stroma
Light-Independent Reactions
Calvin-Benson Cycle
Overall reactants
• CO2
• ATP
• NADPH
Overall products
• Glucose
• ADP
• NADP+
Cyclic! RuBP is regenerated
Figure 7.14_4
• 1st stable molecule is 3C PGA• C3 plants: tomatoes, petunias,
roses, daisies, avocados
C3 Plants
C3 Plants
• Hot, dry days what happens?• Inside leaf?
– O2 increases
– CO2 drops
• PS rate?
C4 Pathway
• CO2 miner
• 4C oxaloacetate forms in bundle sheath cells
• Grasses
CAM Plants
• Opens stomata at night
• Forms 4C compound
• Release CO2
• Succulents and cacti
• Slow growing
C4 and CAM
Greenhouse Effect?
•What is the role of PS in global warming?
– Excess CO2 in the atmosphere
Sunlight
ATMOSPHERE
Some heatenergy escapesinto space
Radiant heattrapped by CO2
and other gases
Greenhouse Effect
Question of the Day
Scientists at Stanford University conducted a study on California grasslands. They looked at the effects of increased levels of CO2 , soil nitrogen, and temperature (modeling our future) on plant growth. What did they find?