A2 SNAB, Detailed steps of Photosynthesis

Both the LIR and LDR, with a diagram to help!

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  • Created on: 18-11-11 17:06
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Stages of Photosynthesis
Light dependant stage of photosynthesis
1. Chlorophyll is in the Thylakoid membrane. The sun emits photons; Chlorophyll in the
Chloroplastabsorbs these photons.
2. The electrons in the Chlorophyll getexcited due to absorbing these emissions, and reach a
higher energy level. The chlorophyllemits the electrons, and therefore becomesoxidised.
This makes the Chlorophyll unstable.
3. Electroncarrierstakein the excitedelectrons and becomereduced. Through a series of
redox reactions the electrons are passed through an electron carrier chain. Giving out
energy as they're being passed down the electron carrier chain less excites the electrons,
energy from this aids ADP becomingphosphorlyated and convertingintoATP.
4. Excited electrons replace already excited electrons which have left the second
photostage to stabilise it again (in non-cyclic phosphotylation the electrons skip
photosystem 1 and return back to photosystem 2) (electron are emitted at the same time
as being replaced)
5. Electron carrier chain take in emitted electrons, the carrier has been reduced and
through a series of redox reactions is passed down the chain.
6. Photon energy breaks water molecules through photolysis,
7. The products of the water molecules are 2H+ and 2E- and 0.5 O2. The 2H+ molecules join
with the 2E- from the carrier chain to form reduced NADP (rNADP). Oxygen is a
by-product.
8. The 2E- from the photolysis reaction replaces the E- from the original chlorophyll to
stabilise it.
Phosphorylation in detail:
1. Phosphorylationoccurs because photolysis breaks water in the lumen. Water breaks
down to 2H , 0.5O2, 2E-. The O2 is released into the atmosphere. The E- goes back to
Photosystem 2 and the H+ ions stay in the lumen.
2. The stalked particle outside of the membrane contains the enzyme ATPasewhich
catalyses photolysis. The 2H+ diffuses out of the membrane and into the stroma. The h+, e-
and NADPthen make rNADP.
Light independent stage of photosynthesis
1. The products from the LDS are carried on into the LIS.
6H20 + ^CO2 6O2 + C6 H12 O2
2. CO2 reacts with RuBP with the aid of the catalyst Rubisco.
3. This makes GP, an unstable 6 Carbon molecule
4. The 6 carbon Molecule breaks down into 2 3 carbon molecules, this stabilises the
molecule.
5. rNADP causes ATP to be reduced, Atp is broken so it's energy can be used to make TP. We
now have NADP and ADP left.
6. TP is 2 3 carbon molecules, TP loses a carbon, ATP energy is then used to rearrange this
unstable 3 carbon molecule and 2 carbon molecule TP into stable % carbon molecule
RuBP again.
7. Every six cycles Glucose is made (through the release of a carbon of Tp at each cycle, and
release of 2H+ ions when rNADP breaks down to NADP) Whilst the cycle is occurring
water is constantly being broken down in the lumen (which is where the 6 O2 comes from)

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