3.2 Light-dependant stage

Where does the light dependant stage take place?

On the thylakoid membranes

What is the source of energy for this stage?

Light (often sun)

What are the products?

ATP, Reduced NADP and Oxygen

What is photophorylation?

The addition of a phosphate ion to ADP using light energy

What does PSI represent?

Photosystem I

What does PSII represent?

Photosystem II

Give a brief description of cyclic photophosphorylation

ATP is produced by electrons that take a cyclical pathway and are recycled back into the chlorophyll a, in PSI

Give a brief descrption of non-cyclic photophosphorylation

ATP is produced by electrons that take a linear pathway from water, through PSII and PSI to NADP, which the electrons reduce

Which phosophosphorylation produces oxygen?

Non-cyclic

In which type of photophosphorylation does photolysis take place?

Non-cyclic

Which type of photophosphorylation reduces NADP?

Non-cyclic

What is the Z scheme?

The pathway taken by electrons in non-cyclic photophosphorylation

Describe the journey of the electrons in cyclic photophosphorylation

PSI --> Electron acceptor --> PSI

Describe the journey of the electrons in non-cyclic photophosphorylation

PSII --> Electron acceptor --> ETC --> PSI

What is photolysis?

The splitting of water molecules by light, producing hydrogen ions, electrons and oxygen

Where does photolysis take place?

In the thylakoid spaces

Give the formula for photolysis

H2O --> 2H+ + 2e- + 1/2O2

What does photolysis contribute to?

- The electrons produced replace those lost from PSII
- The protons from water electrons from PSI reduce NADP
- Oxygen diffuses out into intercellular air spaces, then out the stomata

How is photolysis enhanced?

There is a protein complex in PSII which is the only known enzyme that causes water to be oxidised

What are the 3 factors that maintain the proton gradient between the thylakoid space and the stroma?

- The proton pump associated with the ETC pushing protons into the thylakoid space
- The photolysis of water
- The removal of protons from the stroma, reducing NADP

Summaries the light-dependant stage in one formula

NADP + H2O + 2ADP + 2Pi -----> Red NADP + 1/2O2 + 2H2O + 2ATP