Photophosphorylation.

• Light energy is absorbed by Photosystem II
• The light excites the electrons in chlorophyll, and these electrons move to a higher energy level.
• The high energy electrons move along the electron transport chain to Photosystem I

• As the excited electrons from the chlorophyll leave photosystem II to move along the electron transport chain, they have to be replaced.
• Water is split into oxygen, protons and electrons by light (this is called photolysis).

Overall reaction:

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

• The excited electrons lose energy as they move along the electron transport chain.
• Protons are transported into the thykaloid membranes by using the energy from the excited electrons. This means that the thykaloid membrane has a higher concentration of protons than the stroma, and a proton concentration gradient is formed.
• Protons move down the concentration gradient, and into the stroma; via ATP synthase (an enzyme)
• ATP is formed from this energy from the combination of ADP and an inorganic phosphate. 

• Light energy is absorbed by photosystem I
• This excites the electrons to a higher energy level
• The electrons are transferred to NADP along with a proton (from the stroma)
• This forms reduced NADP

• Only uses photosystem I
• Electrons from the chorophyll molecule aren't passed onto NADP but are passed back to photosystem I via electron carriers (hence cyclic)
• The electrons are recycled
• No NADP or O2 are produced; only small amounts of ATP