Q) Explain how ATP is produced through the light dependent reaction of photosynthesis
Main points | |
Key idea: | Role of light and photosynthetic pigments for the production of ATP during photophosphorylation |
· During photophosphorylation, light energy is required · Ref to absorption of light by photosyn pigments (e.g. chlorophyll a, chlorophyll b, xanthophyll, carotenes, etc) · Ref to location of pigments - embedded in thylakoid membr, chloroplasts) | |
Key idea: | Photoactivation of photosynthetic pigments |
· Light harvesting complexes (comprising of hundreds of photosyn pigments) absorb light energy · Ref to transfer of energy to rx centres (of photosys I and II) · Excitation + displacement of e (of the pair of special chlorophyll a mol) · Pri e acceptor mol received energized e & pass them to electron transport chain (ETC) | |
Key idea: | Synthesis of ATP described by the chemiosmotic theory |
· Energized e transferred fr 1 e carrier to next + down an energy gradient · During transfer, energy rel used by proton pump to transport H+ fr stroma into thylakoid space · Ref to thylakoid membr being impermeable to H+ · Result: H+ conc gradient set up a/x membr; H+ motive force generated · H+ only flow back to stroma via ATP synthase complex in membr · Ref to flow of H+ down gradient coupled to syn of ATP | |
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) The role of light and photosynthetic pigments are both involved in the synthesis of ATP. (v) Chlorophyll absorbs mainly re d and blue-violet light. In photosystem I, the chlorophyll a molecules or primary pigments in the reaction centre absorb light at λ700nm while in photosystem II, the primary pigments absorb light at λ680nm. (vi) Chemiosmosis is an energy-couplng mechanism that uses energy stored in the proton concentration gradient across a membrane to synthesize ATP. Most ATP synthesis in cells are made through this way. | |
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