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4.8 gather and process information from secondary sources to trace the light dependent reaction of photosynthesis on a suitable biochemical pathways flow chart
gather and process information from secondary sources to trace the light dependent reaction of photosynthesis on a suitable biochemical pathways flow chart
- Gather information to locate a biochemical flowchart to trace the light dependent reaction of photosynthesis. To do this you will need to extract information from graphs and tables. See for example:
Photosystem I and II and the Light Reaction
McDaniel College, Westminster, Maryland, USA
- Process the information to illustrate trends and patterns. To do this use the biochemical flow chart of the light dependent reaction to identify:
- in photosystem II, a P680 chlorophyll electron excited by light energy
- manganese atoms that holds two water molecules while electrons are removed one at a time
- the water molecules split into O2(g) and 4H+. The H+ released into the lumen of the thylakoid vesicle
- the electrons in P680 in an excited state (a higher redox or electrode potential)
- the electrons passing from photosystem II (PS II) to the electron accepting quinones in PS II and then down the electrode potential gradient to the cytochrome b – cytochrome f complex that links PS II with PS I
- in the cytochrome b – cytochrome f complex, protons are moved from the stroma to the lumen
- the electron is passed to PS I, the chlorophyll P700 is excited by light and the energy of the excited electrons is increased
- the electrons are transferred to the iron-sulfur centre in ferredoxin and then to NADP+ to form NADPH with H+ from the stroma.
Don’t try to memorise this information but use it to interpret as many diagrams of the light reaction as you can find! You may be interested to know the electrons removed from the water move to fill holes created by light in chlorophyll molecules in the reaction centre of PS II.