1 Photosynthesis Lecture 3 - 4 1 2 What is the moral of this cartoon? Energy can be transformed from one form to another FREE ENERGY (available for work) vs. HEAT (not available for work) 3 THE SUN: MAIN SOURCE OF ENERGY FOR LIFE ON EARTH 4 What is autotrophs? 5 "(17) 172157 Nurul Atiqah Ahmad Food Chain 6 THE FOOD WEB 7 Electromagnetic Spectrum and Visible Light " What is these? " What is the important of visible light to earth 8 Why plants is green? " Explain this phenomena 9
Transcript
1
Photosynthesis Lecture 3 - 4
1 2
What is the moral of this cartoon?
Energy can be transformed from one form to another
FREE ENERGY(available for work)
vs.HEAT
(not available for work)
3
THE SUN: MAIN SOURCE OF ENERGY FOR LIFE ON EARTH
4
What is autotrophs?
5
• (17) 172157 Nurul Atiqah Ahmad Food Chain
6
THE FOOD WEB
7
Electromagnetic Spectrum and Visible Light
• What is these?• What is the important of visible light to
earth
8
Why plants is green?
• Explain this phenomena
9
2
• Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water
AN OVERVIEW OF PHOTOSYNTHESIS
Carbondioxide
Water Glucose Oxygengas
PHOTOSYNTHESIS
10
• The Calvin cycle makes sugar from carbon dioxide– ATP generated by the light
reactions provides the energy for sugar synthesis
– The NADPH produced by the light reactions provides the electrons for the reduction of carbon dioxide to glucose
LightChloroplast
Lightreactions
Calvincycle
NADP+
ADP+ P
• The light reactions convert solar energy to chemical energy– Produce ATP & NADPH
AN OVERVIEW OF PHOTOSYNTHESIS
11
Chloroplasts: Sites of Photosynthesis
• Photosynthesis– Occurs in chloroplasts, organelles in certain
plants– All green plant parts have chloroplasts and carry
out photosynthesis• The leaves have the most chloroplasts• The green color comes from chlorophyll in the
chloroplasts• The pigments absorb light energy
12
• In most plants, photosynthesis occurs primarily in the leaves, in the chloroplasts
• How does a chloroplast look like? • What are the structures can be in a
chloroplast?• Where is chloroplast located?• Any pigment in chloroplast?
• (20) 175007 Azim Syahmi Zafri
Photosynthesis occurs in chloroplasts
13
Structure of chlorophyll
• How does a chlorophyll looks like? • How many types of chlorophyll in a higher
order of plant? And how does these chlorophyll different from each other?
• (21)172138 Nor Syahirah BintiMohd Yusoff
14 15
Light • A form of electromagnetic E that has attributes
of continuous waves and discrete particles (= photon)
• Absorbed by pigment that called photoreceptors
• After absorbing light, pigment becomes excited/unstable
• Excess E must be dissipated as heat, reemitted as light / used in photochemical reaction, thus allowing the pigment to return to its stable ground state
16
Excitedstate
e−
Heat
Light
Photon
Light(fluorescence)
Chlmolecule
Groundstate
Absorption of a photon
Excitation of chlorophyll
in a chloroplast
17 18
3
Photoreceptors
• What is photoreceptors• How many types of photoreceptor in a
higher order of plant and what is their role in a chloroplast?
• (22) 173096 Azman Peli
19
• What is the difference between photoreceptors / photosystem I / photosystem II / reaction centre / light harvesting complex?
• (23) 175045 Muhammad Farid Che Ghani
20
Photosynthesis • Is a 2-stage process that occurs in chloroplast
– Light reactionsØOccur in thylakoidsØInclude light absorption, water splitting, formation of O2
and E chemical intermediate ATP and NADPH ØH2O + NADP+ + ADP + Pi à O2 + ATP + NADPH
– Dark reactions ØOccur in stromaØInvolve utilization of NADPH and ATP to fix CO2 into
CHO in the Calvin-Benson CycleØ CO2 + ATP + NADPH à (CH2O)n + ADP + Pi + NADP+
How the system works?• Light is absorbed by antenna pigments of
PSII and I
• The absorbed E is transferred to reaction centre, P680 in PSII, P700 is PSI
• Absorption of 1 photon of light by PSII removes 1 e from P680
• With its resulting positive charge, P680 is sufficiently electronegative that it can remove 1 e from a molecule of water
….Cont 27
4
• When these steps have occurred 4x, requiring 2 molecules of water, 1 molecule of O2 and 4H+ are released: 2H2O à 4e- + 4H+ + O2
• The e are transferred (by way of plastoquinone –PQ) to the cytochrome b6/f complex where they provide the E for chemiosmosis
• Activation of P700 in PSI enables it to pick up e from the cytochrome b6/f complex (by way of plastocyanin – PC) and raise them to a sufficiently high redox potential that, after passing through ferredoxin (Fd)
• They can reduce NADP+ to NADPH28
29
Low H+
High H+
Electrochemical potential gradient
High
Low
• The sawtooth shifts in redox potential as e pass from P680 to NADP+ have caused this system to be called the Z-Scheme.
• It is also called non-cyclic photophosphorylation because it produces ATP in a 1-way process.
30
Chemiosmosis• Process using H+ movement to join ADP
and Pi. • Accomplished by ATP synthases /
ATPases. • As H+ pass through CF1-ATPase, ADP + Pi
are joined to make ATP. • The movement of H+ through this enzyme
provides the E to make ATP.• An example of facilitated diffusion
31
• The electron transport chains are arranged with the photosystems in the thylakoid membranes and pump H+ through that membrane– The flow of H+ back through the membrane is
harnessed by ATP synthase to make ATP– In the stroma, the H+ ions combine with NADP+
to form NADPH
Chemiosmosis powers ATP synthesis in the light reactions
32
• The production of ATP by chemiosmosis in photosynthesis
Thylakoidcompartment
(high H+)
Thylakoidmembrane
Stroma(low H+)
Light
Antennamolecules
Light
ELECTRON TRANSPORT CHAIN
PHOTOSYSTEM I
33
ATP SYNTHASEPHOTOSYSTEM II
Cyclic Photophosphorylation• Reaction Center: PSI 700 nm• No reduction of NADP+ occurs and e are recycled
Cytb6-f complex: act as e transport chain
e are used to translocate protons which ATPases uses to synthesize ATP
34
Cyclic Photophosphorylation • Cylic reaction transport occurs only occasionally
when synthesis of carbohydrate is curtailed due to limited supply of CO2 and NADPH2 starts accumulating.
• At this time, there would be no need for additional NADPH2. Moreover, the cyclic electron transport serves the purpose of more production of ATP where needed by the chloroplast
35
• Two connected photosystem collect photons of light and transfer the E to chl e
• The excited e are passed from the primary electron acceptor to electron transport chains– Their E ends up in ATP and NADPH
electron transport chains generate ATP, NADPH, & O2
36
Conclusion for light reactions
5
2 H+ + 1/2
Water-splittingphotosystem
PS II
Light
Primaryelectronacceptor
Energyto make
PS I
Primaryelectronacceptor
NADPH-producingphotosystem
Light
NADP+
1
23
How the Light Reactions Generate ATP and NADPH
37
Dark Reactions / Calvin-Benson Cycle
38
Dark reaction
• What do you understand by dark reaction?• There are 3 steps involve in dark reaction.
List out and explain all the steps.
• (28) 174069 Nur Syarina Farhana Darus
39
Calvin-Benson Cycle • Enzyme RuBisCo captures CO2 atm,
release 3-C sugars, later combined to form sucrose and starch.
• Since the first product is 3-C, Calvin cycle also known as C3 cycle.
