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Photosynthesis (Outline)1. Overview of photosynthesis2. Producers, consumers, and decomposers of the ecosystem (source of carbon and
energy) (Autotrophs: photo-autotrophs, chemo-autotrophs, electro-autotrophs, and heterotrophs)
3. Plant structures: organ, tissue, cells, sub-cellular organelle, and molecules.4. Visible Light and its wavelengths5. Overview of the two pathways of photosynthesis
Light reactions: Substrates, products, cellular components and their location Calvin cycle: Substrates, products, cellular components and their location
6. Specifics of the Light reactions and the Calvin Cycle-Light Reactions: The light receptors (Pigments), Photosystems, Location withinchloroplast, Photophosphorylation, Flow of energy-The Calvin cycle: Energy molecules, Carbon source, RuBp, G3P
7. Comparison of chemiosmosis in respiration and photosynthesis8. Photorespiration
Role of RubiscoChallenge to plants on hot dry days Adaptations of C4 and CAM plants
Photosynthesis
Life on the surface of Earth is powered by solar energy that is converted into chemical energy in organic molecules, for use in cellular respiration
Light energy
6 CO2 + 6 H2O
Carbon dioxide Water
C6H12O6+
Glucose6 O2
Oxygen gas
Producers of the ecosystemAutotrophs
Produce their own food and sustain themselves without eating other organisms
Bacteria Algae Plants
Types of autotrophs based on energy source • Photoautotrophs solar energy• Chemoautotrophs chemical energy of inorganic substances.
Bacteria can uniquely oxidize sulfur and ammonia• Electrolithoautotrophs (newly discovered bacteria)
• electrons directly from electric currents are passed through biologic nanowires to heavy metals, not to O2, and are then used to turn CO2 into carbon skeletons
• Several bacterial species with varied mechanisms are found in more common places (mud)
Geothermal Ventshttps://www.youtube.com/watch?v=D69hGvCsWgA
Electric bacteriahttp://www.extremetech.com/extreme/186537-biologists-discover-electric-bacteria-that-eat-pure-electrons-rather-than-sugar-redefining-the-tenacity-of-life
https://www.newscientist.com/article/dn25894-meet-the-electric-life-forms-that-live-on-pure-energy/
Heterot rophs
– consumers and decomposers of the biosphere.
– completely dependent on autotrophs
Leaf Cross Section
Leaf
Mesophyll
Mesophyll Cell
Vein StomaCO2 O2
Chloroplast
Chloroplast
Grana Stroma
TEM
9,75
0×
Stroma
Granum ThylakoidThylakoidspace
Outer membrane InnermembraneIntermembrane space
LM 2
,600
×
In plants, photosynthesis takes place in green leaves
Mesophyll Stoma
Necessary components for Photosynthesis
1.Light 2.Chloroplast
Thylakoids (stacked as grana)The light Reactions
StromaThe Calvin Cycle
Chloroplast
Grana Stroma
TEM
9,75
0×
Stroma
Granum Thylakoid Thylakoidspace
Outer membrane
Inner membrane
Intermembrane space
Light as a source of energy- Solar radiation received by Earth.- Visible light consists of photons of different
wavelengths making up the colors of the rainbow.
Increasing energy
103 nm 106 nm10–5 nm 10–3 nm 1 nm 1 m 103 m
Gamma rays
X-rays UV Infrared Micro-waves
Radio waves
Visible light
380 400 500 600 700 750Wavelength (nm)
650nm
http://science.hq.nasa.gov/kids/imagers/ems/index.html
Light
CO2H2O Chloroplast
LIGHT REACTIONS
(in thylakoids) CALVIN CYCLE
(in stroma)
NADP+
ADP+ Pi
ATP
NADPH
O2 Sugar
An Overview of Photosynthesis
The Light reactions- Converts light energy to chemical energy (ATP & NADPH)- Produces O2 from breakdown of water
The Calvin cycle- uses ATP & NADPH from light reaction to assemble sugar
molecules from CO2
Chloroplasts split water into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules during the light reaction
Specific details of the Light reactions: The Light Receptors
• Photosynthetic Pigments• Different pigments absorb different
wavelengths• Wavelengths that are not absorbed are
reflected or transmitted• Pigments are present within photosystems
LightReflected light
Chloroplast
Absorbed light
Granum
Light-capturing Pigments: Chlorophyll
In chlorophyll an electron from magnesium in the
porphyrin ring that is excited.
CH3 in chlorophyll aCHO in chlorophyll b
Porphyrin ring: light-absorbing “head” of molecule; note magnesium atom at center
Hydrocarbon tail: interacts with hydrophobicregions of proteins inside thylakoid membranes of chloroplasts; H atoms not shown
I. Chlorophyll aparticipates directly in the light reactions
II. Accessory photosynthetic pigments.
Photosynthetic Pigments
1. Chlorophyll bdifferent absorption spectrumfunnels the energy from these wavelengths to chlorophyll a.
2. Carotenoidsfunnel the energy from other wavelengths to chlorophyll aparticipate in photoprotection against excessive light.
Chemistry of autumn leaf color http://chemistry.about.com/library/weekly/aa082602a.htm
II. Accessory Pigments
H2O
LIGHT REACTIONS
ATP
NADPH
Chloroplast
Light
O2
NADP+
ADP+ Pi
CO2
CALVIN CYCLE
[CH2O](sugar)
Leaf Cross Section
Leaf
Mesophyll
Vein StomaCO2 O2
Chloroplast
Chloroplast Components• Light reactions:- Structures: Thylakoid membrane
- Photosystems II & I- Photosynthetic pigments- Electron acceptor
- Electron transport chain- ATP Synthase- Electron transport chain- NADP + Reductase
- Energy and chemical factors: light, Water, ADP +Pi, NADP+
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html#
Light-capturing Pigments: Chlorophyll
In chlorophyll, an electron from magnesium in the
porphyrin ring that is excited.
CH3 in chlorophyll aCHO in chlorophyll b
Porphyrin ring: light-absorbing “head” of molecule; note magnesium atom at center
Hydrocarbon tail: interacts with hydrophobicregions of proteins inside thylakoid membranes of chloroplasts; H atoms not shown
Thylakoid
PhotonLight-harvesting
complexes
Photosystem
Reaction center
STROMA
Primary electron acceptor
e–
Transfer of energy
Special chlorophyll a molecules
Pigment molecules
THYLAKOID SPACE (INTERIOR OF THYLAKOID)
Thyl
akoi
dm
embr
ane
Photosystem consists of a
reaction center surrounded by light-harvesting
complexes
Two types of photosystems that work togetherto use light energy to generate ATP and NADPH.
• Photosystem II• Photosystem I
Splitting of waterhttp://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html#
e–
Mill makes
ATP
e–
ATP
Photosystem II Photosystem I
NADPHe–
e–e–
e–
e–
STROMA(Low H+ concentration)
Light
Photosystem II ytochromeCcomplex Light
2 H+
Photosystem INADP+
reductaseFd
PcPq
H2O THYLAKOID SPACE(High H+ concentration)
1/2O2+2 H+ 2 H+
NADP+ + 2H+
NADPH+ H+
To Calvin cycle
STROMA(Low H+ concentration)
Thylakoid membrane ATP
synthaseATP
ADP+P
H+i
[CH2O] (sugar)O2
NADPH
LIGHT REACTIONS
ATP
LightNADP+
ADP
CO2H2O
CALVIN CYCLE
Light P680
e–
Photosystem II (PS II)
Primary acceptor
Ener
gyof
elec
tron
s
[CH2O] (sugar)
NADPH
LIGHT REACTIONS
ATP
NADP+ ADP
CALVIN CYCLE
LightH2O CO2
O2
e–
e–
2 H+
+1/2 O2
H2OPq
Cytochrome complex
Pc
ATP
P700
e–
Primary acceptor
Photosystem I (PS I)
ee––
NADP+
reductase
Fd
NADP+
+ 2 H+
NADPH+ H+
Light
Electron Flow during the light reaction
A Comparison of Chemiosmosis in Chloroplasts and Mitochondria
• Chloroplasts and mitochondria generate ATP by chemiosmosis, using different sources of energy
• Mitochondria transfer chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP
MITOCHONDRION STRUCTURE
Intermembranespace
MembraneElectron transport
chain
Mitochondrion Chloroplast
CHLOROPLAST STRUCTURE
Thylakoid space
Stroma
ATP
Matrix
ATPsynthase
Key
H+ Diffusion
ADP + P
H+
i
Higher [H+] Lower [H+]
O2
The Calvin Cycle• Uses ATP and NADPH• CO2 enters the cycle and leaves as a 3C
sugar, glyceraldehyde-3-phosphate (G3P).
• Regenerates RuBP
The Calvin Cycle
LightNADP+
ADP+ P i
CO2H2O
Light reactions Calvin cycle
RuBP
G3PATP
Photosystem II Electron transport
chain Photosystem I
O2
Chloroplast
NADPH
3-Phosphoglycerate
Starch (storage)
Amino acids Fatty acids
Sucrose (export)
Leaf Cross Section
Leaf
Mesophyll
VeinStoma
CO2 O2
Chloroplast
• Terrestrial plants face dehydration.• The stomata close to limit loss of water.• This limits amount of CO2 while O2 production continues• A wasteful process called photorespiration• On a hot dry day photorespiration drains 50% of the carbon
that could be fixed by the Calvin Cycle.
Challenge to plants in hot and dry area
Photorespiration
Rubisco can use both O2 and CO2 as substrates and can catalyze a wasteful reaction known as photorespiration when O2is the substrate.
O2 and organic fuel are consumed without producing sugar
Photorespiration is an evolutionary relic
• In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a three-carbon compound
• In C3 plants, a drop in CO2 and rise in O2 whenstomata close on hot dry days divert the Calvincycle to photorespiration
• C3 leaf anatomyLeaf Cross Section
Leaf
Mesophyll
VeinStoma
CO2 O2
Chloroplast
Some plants have special adaptationsto save water and limit “Photorespiration” by separating CO2 fixation from sugar formation
1. C4 plants (spatial separation) corn,sugar cane
2. CAM plants (temporal separation) succulents (cacti and pineapple)
Photosyntheticcells of C4 plantleaf
Mesophyll cell
Bundle-sheath cell
Vein(vascular tissue)
C4 leaf anatomy
StomaBundle-sheath cell
Pyruvate (3 C) CO2
Sugar
Vascular tissue
CALVIN CYCLE
Oxaloacetate (4 CP)EP (3 C)ADPATPMalate (4 C)
CO2PEP carboxylaseMesophyllcell
C4 leaf anatomy and the C4 pathway
• C4 plants minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds in mesophyll cells
• These four-carbon compounds are exported tobundle-sheath cells, where they release CO2 for use in the Calvin cycle
C4 Plants
Sugarcane
C4 plant
CALVIN CYCLE
3-C sugar
CO2
4-C compound
CO2Mesophyll cell
Bundle-sheath cell
• CAM plants open their stomata at night, incorporating CO2 into organic acids.
Stomata close during the day, and CO2 is released from organic acids are used in the Calvin cycle
CAM Plants
CAM plant
Day
CALVIN CYCLE
3-C sugar
CO2
4-C compound
Night
Pineapple
CO2