Chlorophyll a Absorption Peaks — NEET Biology
📚 Practice ConceptFrom can you determine the wavelength (colour of light) at which chlorophyll a shows the maximum absorption? Does it show another absorption peak at any other wavelengths too? If yes, which one?
Which of the following statements about the conversion of light energy into chemical energy during photosynthesis are correct? S1: Chlorophyll a in the reaction center of Photosystem II is known as P700 due to its absorption maximum at 700 nm wavelength. S2: The energy released from the breakdown of the proton gradient across the thylakoid membrane is utilized by ATP synthase to produce ATP. S3: Cyclic photophosphorylation involves both Photosystem I and Photosystem II, resulting in the synthesis of both ATP and NADPH. S4: Water splitting primarily occurs on the outer side of the thylakoid membrane, releasing protons into the stroma. S5: Accessory pigments broaden the range of light wavelengths absorbed and protect chlorophyll a from photo-oxidation.
View solution & NCERT explanation
Correct answer: B — S2 and S5 only
This question focuses on the mechanism of light energy conversion into chemical energy (ATP and NADPH) and the roles of different components in the light reaction. S1: The reaction center chlorophyll a of Photosystem II (PS II) has an absorption maxima at 680 nm, hence it is called P680. P700 refers to the reaction center of Photosystem I. Therefore, this statement is NOT correct. S2: According to the chemiosmotic hypothesis, the breakdown of the proton gradient across the thylakoid membrane (from lumen to stroma) provides the energy for ATP synthase (CF0-CF1 complex) to synthesize ATP. This statement is correct. S3: Cyclic photophosphorylation involves only Photosystem I (PS I). It results only in the synthesis of ATP, not NADPH + H+. Non-cyclic photophosphorylation involves both photosystems and produces both ATP and NADPH. Therefore, this statement is NOT correct. S4: The splitting of water (photolysis) is associated with PS II and occurs on the inner side of the thylakoid membrane (lumen), releasing protons into the lumen. Therefore, this statement is NOT correct. S5: Accessory pigments (like chlorophyll b, xanthophylls, and carotenoids) absorb light at different wavelengths and transfer the energy to chlorophyll a, thus enabling a wider range of light utilization. They also protect chlorophyll a from photo-oxidation. This statement is correct. Thus, statements S2 and S5 are correct.
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