1. 4.3 Photosynthesis

2. Photosynthesis in Plants
What is the simple word equation for photosynthesis?

3. Chloroplasts
Thylakoids are a phospholipid bilayer membrane-bound compartment. A granum is a stack of thylakoids folded on top of one another. The stroma is the fluid space within the chloroplast. The lumen is the fluid filled space within a thylakoid.
An average green plant cell has between 10 – 50 chloroplast

4. Chlorophyll Chlorophyll is actually made up of 5 pigments
Chlorophyll a & b
Carotenoids (carotene and xanthophyll)
Phaeophytin (a grey breakdown product of the others)

5. There are 2 distinct chlorophyll complexes
Photosystem I (PSI)
Photosystem II (PSII)
Each system has a different combination of pigments
They therefore absorb light in different areas of the spectrum
PSI absorbs around 700 nm
PSII absorbs around 680 nm
Each system has a different role in photosynthesis

6. Biochemistry of Photosynthesis
Photosynthesis is a two stage process involving a series of reactions.
Light-dependent stage can only take place during daylight.
It produces products which are used by the light-independent stages.
The whole process occurs all the time during daylight hours. But the light-independent stage can also occur in the dark.

7. Light-Dependent Takes place on thylakoid membranes 2 functions:
Produce ATP
Split water in a photochemical reaction providing hydrogen ions to reduce CO2 and make carbohydrates
Light is made of photons, photons hit chlorophyll and excite them (give them more energy)
excited electrons are picked up by electron acceptors
ATP can then be made by photophosphorylation via an electron transport chain.

8. Cyclic Photophosphorylation

9. Non-Cyclic Photophosphorylation
NADP (electron acceptor)
+2H+
Reduced NADP (used in light-independent reaction)
Electron transport chain

10. Light-independent Stage
CO2
Glucose
Ribulose bisphosphate (RuBP) 6C
2 GP (glycerate 3 phosphate)
2 GALP (glyceraldyde 3 phosphate)
RUBISCO
Calvin Cycle
1st step CO2 combines with a 5C molecule RuBP, carbon is “fixed” using Enzyme ribulose bisphosphate carboxylase/oxidase (RUBISCO).
Makes a theoretical 6C compound
That splits to make 2, 3C compounds (GP)
This is reduced to make a 3C sugar (GALP) using reducedNADP and ATP
GALP then used to replace used up RuBP, some left over to stick 2 together and make glucose.