July 31, 2021
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!