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Photosynthesis
Friday, 15 August 2014

7:57 PM

a
...
Light energy, in the form of protons, hit and activates the photosynthetic pigments in the photosystems of the
thylakoid membrane, it results in the photoactivation of the pigments, releasing a pair of excited electrons
...
Chlorophyll a and b
i
...
Chlorophyll a is most abundant → Primary pigment → Directly converts solar energy to chemical energy
(excited electrons)
iii
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Carotenoid
i
...
Func ons mainly as an accessory pigment → Absorbs wavelengths of light that chlorophylls cannot
2
...
The lost electron pair is replaced via the photolysis of water, which also produces hydrogen ions and
oxygen
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Photosystem I: Reac on centre contains a pair of P700 chlorophyll a molecules → Absorb λ700nm light
b
...
The electrons are then passed from one electron carrier to the next of a lower energy level via chemiosmosis, till the
final electron acceptor, NADP, which is reduced to NADPH/H+
...

a
...
Photosystem II → Primary electron acceptor on ETC → Photosystem I → ETC → NADP
b
...
Photosystem I → ETC → Photosystem I
4
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Outline the three phases of the Calvin cycle:
i
...
carbon reduction
iii
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1
...

2
...
The triose phosphate molecules are then linked together to form
glucose phosphate, which is used to form starch
3
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RuBP regeneration
Some of the triose phosphate produced is used to regenerate RuBP to continue the cycle, catalysed by
the addition of ATP
c
...

Light
intensity
Low

Rate-limiting step

Reason

Effects

Carbon reduction of
glycerate-3-phosphate,
which is catalysed by ATP
and NADPH

ATP and NADPH is generated from the phosphorylation of ADP to
ATP by ATP synthase, and the reduction of NADP as a final
electron acceptor in photosystem II

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