- Light reactions or the ‘photochemical’ phase include light absorption, water splitting, oxygen release, and the formation of high-energy chemical intermediates, ATP and NADPH..
- The pigments are organised into two discrete photochemical light harvesting complexes (LHC) within the Photosystem I (PS I) and Photosystem II (PS II).
- The LHC are made up of hundreds of pigment molecules bound to proteins.
- Each photosystem has all the pigments (except one molecule of chlorophyll a) forming a light harvesting system also called antennae.
- The single chlorophyll a molecule forms the reaction centre.
- In PS I, the reaction centre chlorophyll a has an absorption peak at 700 nm, hence is called P700, while in PS II it has absorption maxima at 680 nm, and is called P680.
Fig. Light harvesting complex