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The second part of the IBDP Biology Blog post will look into more depth regarding the light dependent reactions and the ways in which energy is used.
Light Dependent Reactions
- A photon of light is absorbed by a pigment in Photosystem ii and transferred to other pigment molecules until it reaches one of the chlorophyll A molecules in the reaction centre
- The photon energy excites one electron within the Chlorophyll A so that it is raised to a higher energy state
- This electron is captured by the primary acceptor of the reaction centre
- Photosystem ii replaces the excited electron before any more photons are absorbed through the process of Photolysis
- Photolysis: Using light water is split by an enzyme to produce electons [given one by one to chlorophyll A in reaction centre] hydrogen ions [contribute to proton gradient] and an oxygen atom [waste gas]
- The excited electrons pass from the primary acceptor down an electron transport chain (though a chain of carriers) loosing energy at each exchange (as they pass each carrier)
- Enough energy is released to pump protons across the Thylakoid membrane from the stoma into the space or lumen inside Tylakoid creating a proton gradient
- ATP Synthase diffuses protons across membrane
back into Stroma and uses the energy of the protons to produce ATP
Chemiosmosis: Generation of ATP using energy released by movement of hydrogen ions across membrane
Photophosphorylation: Production of ATP in Chloroplasts
Energy is needed - this energy is obtained by absorbing light
- At the end of the Electron Transport Chain electrons are passed to Photosystem i
- A pair of excited electrons is emitted from the reaction centre of Photosystem i and passes along a chain of electron acceptors
- At the end of the chain electrons are passed to NADP Reductase in membrane
- NADP is reduced to NADPH by accepting the two electrons from Photosystem 1 and two Hydrogen ions from Stoma
That is all for the second part of LDR!
