Which of the following photosynthetic pigments serves as the primary reaction center in both Photosystem I and Photosystem II, while all other pigments act as accessory antenna pigments?
Answer and explanation
Correct answer: A. Chlorophyll a
- Step 1: Photosynthetic pigments include chlorophyll a, chlorophyll b, carotenoids (carotenes and xanthophylls).
- Step 2: Chlorophyll a forms the specific reaction centers: P680 in Photosystem II and P700 in Photosystem I.
- Step 3: Chlorophyll b and carotenoids function as accessory pigments that harvest light over a broader spectrum and transfer excitation energy via resonance transfer to chlorophyll a, while also shielding chlorophyll a from photo-oxidation.
Answer
Chlorophyll a
Why not the others: 'Chlorophyll b' is an accessory pigment with an aldehyde group (-CHO) instead of a methyl group (-CH3); 'Lutein (xanthophyll)' and 'Beta-carotene' are accessory carotenoids providing photoprotection by quenching reactive singlet oxygen, but neither forms reaction centers.
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