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WAEC Biology 2005 Question 23

Question 23

Transport in Plants

A faster colour change of a dry cobalt chloride paper affixed to the lower surface of a leaf than the upper one, indicates that

  1. A.sunlight slows down water loss from the upper surface
  2. B.the lower surface of the leaf has more stomata
  3. C.sunlight causes the stomata on the upper surface to close
  4. D.stomata are not present on the upper surface of a leaf
Show the answer and explanation

Answer: B (the lower surface of the leaf has more stomata)

Explanation

Cobalt chloride paper turns from blue to pink with water; it changes faster on the lower surface because more water vapour escapes through its many stomata.