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8/11/2019 7.2 Light Dependent Reaction
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PhotosynthesisChapter
7.1 Introduction to photosynthesis
7.2 Light dependent reaction
7.3 Light independent reaction
7.4 Factors limiting the rate ofphotosynthesis
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Explain the conversion of light energyinto ATP and NADPH
OBJECTIVE :
At the end of this lesson, students shouldbe able to :
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KEYTERMS Light Dependent Reactions Photophosphorylation Non-cyclicphotophosphorylation Cyclic photophosphorylation
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Overview:7.2 Light Dependent Reactions
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7.2 Light Dependent Reactions
Light dependent reaction
Occurs in the presence of
light
Occurs in the grana
The light dependentreaction converts lightenergy to chemicalenergy (ATP andNADPH)
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Photophosphorylation
The formation of ATP which occurs duringthe light dependent stage of photosynthesis(ATP production in photosynthesis)
2 types of photophosphorylation:-
(a) The non-cyclic photophosphorylation
(b) The cyclic photophosphorylation
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THE NON-CYCLIC
PHOTOPHOSPHORYLATION
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STEPS IN NON-CYCLICPHOTOPHOSPORYLATION
Step 1i) Light strikes photosystem II - causes
electrons to be ejected
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ii) These electrons are accepted by electron
acceptor
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Step 2
i) Electrons from the acceptor pass through aseries of electron transport chain
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ii. The electrons lose energy until they reach for
the Photosystem I
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iii) The energy released is used to form ATP-
photophosphorylation
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Step 3
i) PSI absorbs light energyii) Electrons are ejected from PS1iii) PS1 receives electrons from PS1
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iv) The ejected electron are accepted by electron
acceptorv) The electron and hydrogen ions (H +) are usedto NADP to NADPH
vi) Protons are produced by photolysis of water
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Photolysis of water
i) Photolysis is the process of splitting watermolecules using light energy with the releaseof electrons and protons (H+) and oxygen.
ii) Proton from H 2O reduce NADP to NADPH 2iii) Electrons from H 2O used to replaced
electrons missing from photosystem IIiv) Oxygen atom is released as a by-product
that used in cellular respiration
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NADPH & ATP produced are used inthe light independent reactions orCalvin Cycle
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CYCLICPHOTOPHOSPORYLATION
The electrons from PS1 also be recycledto PSI
Produced only ATP known as cyclicphotophosphorylation
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Electron from PSI may pass back tothe ETC and to PS1 after they areejected
As the electron pass along the ETC,
ATP is formed
CYCLIC
PHOTOPHOSPORYLATION
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Light dependent reactions use light
energy to produce ATP & NADPH
Involves PSI & PSII
Conclusion
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