OCR Biology A-Level Photosynthesis Summary

Granum : Stacks of thylanoids
Thylanoids :
flattened sacs formed by the membrane

Lamellae Granum joined membranous Channels
by
:




Chlorophyll Green pigment which absorbs
light
:




Light-dependent stage of photosynthesis
Non-cyclic photophosphorylation
·
:




absorbed
Light
1 is
exciting electrons in the
photosystem 2 centre
.

,



2 .
Electrons are
passed to an electron
transport chain
producing some ATP
by chemiosmosis
.
3
Electrons lost from PS2 are
replaced with electrons produced by photolysis
4.
Electrons arive at PSI and are
again passed to an electron transport chain

s .
These electrons
along with anttion are accepted by the NADP
Coenzyme
6 reduced
NADP is
producing NADPH for other
processes
.




Photolysis
·
:



↳ breaus water down into 02 2H+ and Ze
Energy from the sun ,



↳The Le PS2
replaces dectrons lost from the centre

↳ 2H+ reduction of NADP
Catalyses the to NADPH

Cyclic Phosphorylation
·
:



↳ Electrons
leaving the transport chain after psi can return to PSI rather than


reducing NADP
↳ PSI NADPH
can still produce ATP but not


light independent photosynthesis :
Takes place in the stroma
using
NADPH and ATP

Calvin Cycle :




.CO2 is combined with Ribulose bisphosphate (Scarbon molecule) by RuBis Co enzyme
2 .

Unstable six carbon compound forms and breaks down into two three carbon

Glycerate 3-phosphate (GP) molecules


NADPH and
light dependent turn ap triose phosphate (TP)
3 .
ATP from the reactions into

4 Most TP is recycled Ribulose bisphosphate and synthesise
.
to
regenerate complex
molecules .