Photoionisation of Chlorophyll
Biology: AQA A Level, topic 5.1.2
Photoionisation of Chlorophyll
The first step of the light-dependent reaction is the absorption of light energy by chlorophyll. This causes photoionisation, which is the release of electrons.
Light absorption
- Light energy is absorbed by chlorophyll in the photosystems. This is the first step in photosynthesis.
- Absorbing light energy excites the electrons within the photosystem.
- The electrons are now in a more excited state. This causes them to be released from the chlorophyll.
- Chlorophyll is now considered to be photoionised.
Energy from photoionisation
- The photoionisation of chlorophyll also results in a release of energy.
- This energy is used in photosynthesis to drive three reactions:
- Photophosphorylation - production of ATP from ADP and inorganic phosphate.
- Reduction - production of reduced NADPH from NADP.
- Photolysis - splitting of water into protons, electrons and oxygen.
- These three reactions are necessary for photosynthesis to take place.
Test yourself on Photoionisation of Chlorophyll
Which of these reactions is NOT driven by energy from photoionisation of chlorophyll?
What causes the electrons in chlorophyll to become excited?
Which of the following statements are true about chlorophyll photoionisation?