A2 Edexcel Biology: Light-Dependent Reactions

Light hits a chlorophyll molecule, transferring the energy to the electrons of the molecule.
The electrons become excited and are raised to a higher energy level.
If the electrons' energy level is raised significantly it will leave the chlorophyll molecule completely.
The excited electron will then be picked up by an electron acceptor and is used in the synthesis of ATP via either cyclic or non-cyclic photophosphorylation.

This involves only photosystem I and will only produce small amounts of ATP.
The light hits the chlorophyll molecule in PSI, exciting the electron and causing it to leave the molecule.
it's taken up by an electron acceptor and passed directly along an electron transport chain to create ATP.
The electron then returns to the chlorophyll molecule in PSI and cna be excited in the same way.
The electrons are recycled and can repeatedly flow through PSI.

Light energy is absorbed by PSII and excites the electrons in the chlorophyll, moving it to a higher energy level.
The electrons are then able to leave the chlorophyll and be taken up by an electron acceptor.
The electrons that leave the chlorophyll in PSII, must be replaced.
light energy will then split water into protons (H ions), electrons and oxygen.
The electrons that have been take up by the electron acceptor then move along the electron transport chain, causing them to loose energy.
The energy that is released is used to convert ADP and Pi into ATP.
These electrons will enter another chlorophyll molecule in PSI, where they become excited to an even higher level by more light energy.
Eventually they pass to NADP, and with the hydrogen from water form reduced NADP.

A2 Edexcel Biology