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My own note in understanding photosynthesis for subject JIB 224 Plant Physiology
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By Alex
PHOTOSYNTHESIS
Glucose
Light
Carbon Dioxide
Water
Oxygen
6CO2 + 6H2O + Energy (Light) C6H12O6 (glucose) + 6O2
Complex series of reactions that takes place in two stages:
1. Light reaction (light dependent) 2. The Calvin cycle - Carbon Fixation ( Light
independent)
Light reactions Calvin Cycle (Carbon Fixation)
• Trap the energy from sun & use it to form ATP + Hi energy electron
• Split water - replenish Electrons & H+ (carried by NADPH)
• and released Oxygen
IN OUT
• form ATP • NADPH • Oxygen
• Carbon dioxide in the air • Electrons & Hydrogen deliver by NADPH • powered by ATP • Carbon dioxide, H+, and electron are rearranged
in to glucose with high energy level
ATP supply
The nature of light • Light is energy emitted as photons which acts both particle and waves • Different wavelength of light carry different amount of energy • The shorter the wavelength, the higher the energy • Different wavelength= different color • Sunlight is a mixture of different wavelength;
R O Y G B I V Longer Wavelength shorter Lower Frequency higher Lower Energy higher
When the sunlight hit the plant, the energy is absorbed by the pigments. Different pigments absorbs different wavelength. If the wavelength not absorbed, it is reflectd. Chlorophyll is the major photosynthetic pigment. It i absorbing some wavelengh but reflecting green.
By Alex
Cyclic Electron Transfer
Non- Cyclic Electron Transfer
WHERE IS CHLOROPHYLL?
Chloroplast • are a double membrane bound organelle Thylakoid • The stacks of pillow shapped membranse are filled with
chlorophyll and enzymes where light reactions occur Stroma • The fluid filling the rest of the chloroplast contain certains
enzyme for the Calvin Cycle
Photosytem L i g h t h a r v e s t i n g c o m p l e x e s e m b e d e d i n t h e t h y l a k o i d m e m b r a n e s c l u s t e r s o f photopigment- chlorophyll a, chlorophyll b and carotenoids.
1. Photon strike electron (chlorophyll) 2. The energy is absorbed causing 3. The electrons to jumpp & bound in energy on the photosystem 4. Reach to reaction centre chlorophyll 5. Electron acceptor come in, pick the electron to the ETC
Photosystem I (P700)
Photosystem II (P680)
Reaction Centre Chlorophyll
Electron Transport Chain (ETC) • Series of enzymes embedded in a membrane • Electrons are passed slong from one molecule to the
next and energy is given off to make ATP*
• As electron is moved, it drives the pumping of Hydrogen ions onto one side of a membrane creating concentration and electrical gradient to build.
• It is this gradient that drives the production of ATP.
By Alex
Photosytem L i g h t h a r v e s t i n g c o m p l e x e s e m b e d e d i n t h e t h y l a k o i d m e m b r a n e s c l u s t e r s o f photopigment- chlorophyll a, chlorophyll b and carotenoids.
Occur in thylakoid membrane
Cyclic Electron Transfer
CYCLIC ELECTRON TRANSFER 1. When, light (photon) strike electron (chlorophyll), the energy is absorbed and boost the electron to high energy level. 2. This energized electrons jump & bound [in energy] around the photosystem. 3. The electron then reach special chlorophyll a [called the reaction centre] 4. The electron kept by electron acceptor. 5. The electron acceptor deliver the electron to the Electron Transport Chain 6. The electron will move down ETC in a series of Oxidation-Reduction reaction [Redox reaction] 7. As electron move down the ETC, energy given off to make ATP 8. By the time electron move down ETC, it is no longer high energy electron. 9. The electron then return to P700 [Photosystem I].
Since the electron getting back where it begun, so it is a cyclic electron transfer.
Photosystem I (P700)
1
2
43 e-
7
65
8
9
e-
Energy to make ATPATP
Photophosphorylation
By Alex
Non- Cyclic Electron Transfer
Photosystem II (P680)
P680 (PSII) P700 (PSI)
Energy to make ATPATPe-
e-
e-
e-
e-
NADP+ + e- + H -->NADPH
Photolysis H2O --> O2 + H + e-
Replinish electron lost from P680
NON- CYCLIC ELECTRON TRANSFER 1. When, light (photon) strike electron (chlorophyll), the energy is absorbed and boost the electron to high energy level.
• This energized electrons jump & bound [in energy] around the photosystem. • The electron then reach special chlorophyll a [called the reaction centre] • The electron kept by electron acceptor.
2. The electron acceptor deliver the electron to the Electron Transport Chain • The electron will move down ETC in a series of Oxidation-Reduction reaction [Redox reaction]
3. As electron move down the ETC, energy given off to make ATP 4. By the time electron move down ETC, it is no longer high energy electron. 5. The electron then enter to P700 [Photosystem I] and again, light strike the electron to boost it to high energy
electron. • The electron bound around PSI, and reach special chlorophyll a [reaction centre] • The electron then kept by electron receptor
6. Electron receptor deliver the electron to short ETC. 7. At the end, electron e- combine with H+ & NADP+ to form NADPH molecule.
Photolysis • Water supply is broken by photom to form e-, H+ and Oxygen molecule • E- replinish electron supply in PSII • H+ combine with NADP+ to form NADPH • Oxygen molecule released to atmospheric air
Since the e- doesn't back to P680,then it's known as NON-cyclic electron transfer.
23
5
4
1
7
6
1i
8
Photophosphorylation
Calvin Cycle
By Alex
Photophosphorylation
1
2 3
4
5
6
Light (photon) strike electron (chlorophyll), the energy is absorbed and
boost the electron to high energy level
The high energy electron is picked up by electron receptor called
plastiquinone[PQ] and brought to ETC
Electron need to grab proton [H+] to going down the ETC [Cytochrome complex], As electron go down, it pulls the proton
with it. And H+ ion pump to the inside thylakoid membranethrough. Electron back to ground state[no longer high
energy electron]. Non cyclic pathway. Enter to PS1.
The electron is brought by PC [ ] to P700 [PS1]
The high energy electron is picked up by electron receptor called ferrodoxin[Fd]
and brought to ETC
The electron again strike by light, boost the electron to high energy level
The electron deliver to ETC pickup by NADP+. The ETC not only transport foe
electrom but also reduce NADP reductase.
Hydrogen ion (H+) pump into the thylakoid membrane derived from: • Hydrogen ion grabbed by electron to paass through ETC ( cytochrome complex) • From photolysis in which water break donating electron to PS11 and giving H+ to thylakoid
membrane The hydrogen ion cant pass through the phospholipid bilayer. The accumulate hydrogen ion cause the gradient of hydrogen ion inside the thylakoid membrane became high. A special tunnel in membrane, ATP synthase is a s special for pumping the hydrogen ion out by using the gradient different between inside the thylakoid membrane and stroma. The hydrogen ion taht pump out via ATP synthase used as energy to combine ADP and Pi to form ATP.