1.Explain either how the light reactions of photosynthesis make ATP and NADPH an
ID: 78373 • Letter: 1
Question
1.Explain either how the light reactions of photosynthesis make ATP and NADPH and generate oxygen OR how mitochondria make ATP
Include the following information
Brief explanation. Use your figure to indicate:
Source, flow and ultimate acceptor of electrons (electron donors and acceptors must be shown in the correct position relative to the membrane).
Proton pump(s) and direction of proton pumping
Orientation of the ETC by indicating the stromal or matrix side
Identify the components of ETC in the figure.
Show where ATP is produced and what powers the production of ATP
Brief explanation.
Loose tightExplanation / Answer
Light reaction take place inside thylokoids and involve absorption of light energy by photosynthetic pigment and its conversation into chemical energy in the form of ATP I e photophasphorylation and photolysis of water leading to formation of NADPH2 and liberation of oxygen.
Photophasphorylation
Formation of ATP in the chloroplast by photosynthesis is called photophasphorylation.
Cyclic photophasphorylation
It is a process of photophasphorylation in which an electron expelled by the excited photocenter is returned to it after passing through a series of electron carriers.
It occurs under conditions of low light intensity
It is more efficient in ATP production as 4 ATP per 6photon is produced in it.
Non cyclic photophasphorylation
It is normal process of photophasphorylation in which the electron expelled by the excited photocenter do not return to it.
non cyclic photophasphorylation is carried out in collaboration of both photosytem 1 and 2 .
Electron released during photolysis of water are picked up by photocenter of PS 2 called P680 . It is passed through aa series of electron carriers - phaeophytin, PQ, cytochrome b6 f complex and plastocyanin in a downhill journey releasing energy at each step.
While passing over cytochrome complex, the electron loses sufficient energy for the synthesis of ATP.
The electron is handed over to photocenter p700 ofPS 1 by photocyanine . P700 extrudes the electron which passes through special chlorophyll X, Fe-S complex, ferredoxin to finally reach NADP+ .
The latter then combine with H+ with the help of NADP-reductase to form NADPH.
This is called Z scheme due to its charecterstic zig-zag shape besed on redox potential different electron carriers.
photolysisof water
photocatalytic splitting of water is the phenomenon of breaking up of water into hydrogen and oxygen.
It is carried out by oxygen evolving complex present in PS2 and is attached to inner surface of thylakoid membrane.
oxygen evolving complex has 4 Mn Ions and 2 other Ca2+ and Cl- which helps in liberation of oxygen.
The light energised changes in My removes electron from OH-component oof water forming oxygen .
Electron expelled carrier transfer the released electron to P680
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