BRAINCAKEPhotosystems
In the thylakoid membranes, pigment molecules are not scattered randomly. They are grouped with proteins into photosystems, each of which works like a funnel for light energy.
A photosystem has two parts:
• a light-harvesting complex (antenna complex): hundreds of chlorophyll a, chlorophyll b and carotenoid molecules held by proteins. When any of them absorbs light, the energy is passed from pigment to pigment towards the centre.
• a reaction centre: a special pair of chlorophyll a molecules. When energy reaches it, an electron in the chlorophyll is excited to a higher energy level and leaves the molecule. It is taken up by an electron acceptor, and the chlorophyll is left oxidised.
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More in Photosynthesis
- Chloroplasts
- Chlorophyll
- Absorption Spectrum Chlorophyll
- Chromatography
- The Light-Dependent Reactions
- Cyclic Photophosphorylation
- Non-Cyclic Photophosphorylation
- The Light-Independent Stage
All 20 lessons in Photosynthesis · All Edexcel A-level Biology topics