A2 Biology - Photosynthesis

LIGHT-DEPENDANT STAGE

1. Photons of light raises 2 electrons to a higher energy level in PSII. They are then released, and captured by an electron-acceptor molecule. The PSII has now been oxidised, and so recieves 2 electrons from the photolysis of water. 

2. Electrons in the electron acceptor molecule pass along a series of electron carrier molecules, all of which are embedded in the thylakoid membranes. These molecules constitute the electron transport chain. 

3. This transfer of electrons from one carrier to the next is done through a series of REDOX reactions. Energy is released and enabled ADP to join with inorganic phosphate (Pi) to form ATP. Light energy has therefore been converted to and stored as chemical bond energy in ATP. This is non-cyclic photophosphorylation. 

4. Photons of light energy are harvested by PSI. The electrons in PSI are raised to a higher energy level, and then released to another electron-acceptor molecule. PSI has been oxidised, and so takes electrons from the previous transport chain. 

5. Some electrons…