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Expression of IdeasMediumExplaining why leaves turn yellow

Expression of Ideas practice question

While researching a topic, a student has taken the following notes: - Chlorophyll gives leaves their green colour and masks other pigments in the leaf. - In autumn, trees stop producing chlorophyll. - The yellow and orange pigments that were already in the leaf become visible. - Some trees also produce red pigments in cool, sunny weather.

The student wants to explain why leaves turn yellow in autumn. Which choice most effectively uses relevant information from the notes to accomplish this goal?

  1. A. In autumn trees stop making chlorophyll, and the yellow and orange pigments it had been masking become visible.Correct
  2. B. Leaves turn yellow and orange in autumn.
  3. C. Some trees produce red pigments in cool, sunny weather.
  4. D. Leaves turn yellow because they absorb yellow light from the low autumn sun.

Answer: A. In autumn trees stop making chlorophyll, and the yellow and orange pigments it had been masking become visible.

The goal asks WHY. Choice A gives the mechanism: chlorophyll stops, the masked pigments show.

Why the other answers are wrong

B. Leaves turn yellow and orange in autumn.
This states the fact to be explained, not the explanation.
C. Some trees produce red pigments in cool, sunny weather.
This is about red pigments, not yellow.
D. Leaves turn yellow because they absorb yellow light from the low autumn sun.
Nothing in the notes concerns absorbing yellow light.

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