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Harvesting Light
· Accessory pigments (chlorophyll b and
carotenoids) and primary pigment (chlorophyll a)
found in thylakoid membranes of chloroplasts in
group/clusters called antenna complexes
· Photons of light passed from accessory pigments
to the primary pigment (chlorophyll a) in a
reaction centre
· Two types of reaction centre, photosystems 1
and 2…read more

Slide 3

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Light Dependent Stage
· Takes place in thylakoids of chloroplasts
· ADP and Pi synthesised to ATP by
photophosphorylation
· Water is split into 2H+, 2e-'s and ½ O2 by
photolysis
· NADP is reduced by 2H+'s from photolysis of
water
· Two forms of LDS cyclic
photophosphorylation and non-cyclic
photophosphorylation…read more

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Non-Cyclic Photophosphorylation
· Also known as Z-scheme
· Light absorbed by PSII and passed on to chlorophyll a (P680)
· Chlorophyll a emits 2 e-'s, which are raised to a higher energy level and picked up
by an electron acceptor
· Electron's passed along a chain of carrier molecules until it is eventually accepted
by PSI
· Energy released when electrons are passed down chain of carrier molecules is
used for photophosphorylation of ADP and Pi to ATP
· Light absorbed by PSI and passed onto chlorophyll a (P700), which emits 2 e-'s
· Electrons raised to higher energy level and picked up by an electron acceptor
· Electrons passed down (shorter) carrier molecule chain until accepted by NADP
· Photolysis of water produces 2H+, which combines with NADP to give reduced
NADP, 2e-'s which replace electrons lost from PSII and ½ O2 which is emitted as a
waste product
· Reduced NADP and ATP passed onto light independent stage…read more

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Cyclic Photophosphorylation
· Only involves PSI
· Light absorbed by PSI and passed onto chlorophyll a (P700)
· Chlorophyll a molecule emits an electron
· Electron is raised to a higher energy level and is picked up by an
electron acceptor
· Electron passed along a carrier molecule chain until it recombines
with PSI
· Energy emitted when electrons are passed along carrier molecule
chain used for photophosphorylation of ADP and Pi to ATP
· No reduced NADP is made
· ATP is passed onto the light independent stage…read more

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Chemiosmosis
· ATP is synthesised form ADP and Pi by enzyme ATP
synthetase found in the thylakoid membranes
· Energy emitted as electrons are passed down the
carrier molecule chain in light dependent stage used to
pump hydrogen ions from stroma to the thylakoid
membrane space, creating an electrochemical
gradient across the thylakoid membrane
· Hydrogen ions diffuse down the electrochemical
gradient through the thylakoid membrane via protein
channels
· Shape of ATP synthetase changed so that ATP can be
synthesised from ADP and Pi…read more

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