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Why do leaves of many trees turn yellow before falling in autumn?

  • (a) Chlorophyll is converted directly into xanthophyll. Your answer
  • (b) Chlorophyll breaks down and unmasks the yellow pigments. Correct
  • (c) Carotenoids are made fresh in very large amounts. Your answer
  • (d) The stroma of chloroplasts turns yellow with starch. Your answer
Your answer: Correct answer: (b)
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Explanation

Why (b) is correct

In autumn, chlorophyll breaks down. The yellow pigments (carotenoids and xanthophylls) that were present all along are no longer masked, so the leaf looks yellow.

Why the other options are wrong

  • (a) · your answer Chlorophyll is not converted into xanthophyll; it simply breaks down.
  • (c) · your answer Carotenoids were already present; they are unmasked, not made fresh.
  • (d) · your answer Starch does not make the stroma yellow.
NCERT point: Leaf colour depends on the mix of pigments present.
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Practise Photosynthesis in Higher Plants
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