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Question 83

Strips of a chemical that changes colour when it gets wet are fixed to both surfaces of one leaf. Which surface shows the greater water loss, and why?

  1. The upper surface, because it faces the sun and gets hotter
  2. Both equally, since water leaves through the whole leaf surface
  3. The lower surface, because most of the stomata are thereCorrect answer
  4. The upper surface, because its waxy layer is thinner

Explanation

Vapour can only escape where there are pores for it to pass through, and in a typical leaf far more pores are set into the shaded underside, so that is where the colour change appears first and strongest. The sunlit top does get warmer, but warmth cannot drive vapour out of a surface that offers it almost no openings.

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Question 83: Strips of a chemical that changes colour when it gets wet… · Plants and Photosynthesis · Questena