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NEET 2018 · BiologyPrevious Year Question

Oxygen is not produced during photosynthesis by

Answer: (C) Green sulphur bacteria. Oxygen evolution in photosynthesis comes from the splitting of water (H2O is the hydrogen donor in green plants, cyanobacteria like Nostoc, and algae like Chara, and in Cycas).

  1. A.Cycas
  2. B.Nostoc
  3. C.Green sulphur bacteria✓
  4. D.Chara

Correct Answer

(C) Green sulphur bacteria

Solution & Explanation

Oxygen evolution in photosynthesis comes from the splitting of water (H2O is the hydrogen donor in green plants, cyanobacteria like Nostoc, and algae like Chara, and in Cycas). Green and purple sulphur bacteria use H2S instead of H2O as the hydrogen donor, so their oxidation product is sulphur or sulphate, not O2 — anoxygenic photosynthesis. Therefore oxygen is not produced by green sulphur bacteria (C). NCERT: Class 11 Ch 11, p.135 [135:065–135:068]: "the ‘oxidation’ product is sulphur or sulphate depending on the organism"

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