• Question: Why do leaves change color in the fall?

    Asked by dalvindk to Damien, Rachael, Simon, Suzi, Tim on 16 Jun 2011.
    • Photo: Suzi Gage

      Suzi Gage answered on 14 Jun 2011:

      Hi @dalvindk
      I didn’t know the answer to this but I’ve looked it up and it’s really cool.
      The green colour of leaves is chlorophyll (I remembered that from my school days 🙂 ). When autumn gets here and the days get shorter, the chlorophyll can’t get enough light to photosynthesize (create oxygen from carbon dioxide) so the chlorophyll disappears. The leaves look orange or brown because that colour was there all along, but masked by the green chlorophyll. Some go purple because of trapped glucose in the leaves, which goes purple or red while it’s trapped.

      Hope this answers your question 🙂

    • Photo: Damien Hall

      Damien Hall answered on 16 Jun 2011:

      I think it has something to do with the proportions of different chemicals that are near the surface of the leaf, and that’s controlled by the temperature. If I remember it right (and that’s a big “if”!), the chemical that causes greenness is called chlorophyll and the chemical that causes yellowness is called xanthophyll. If it’s warmer, there is more chlorophyll closer to the surface of the leaf, and, if it’s colder, there is more xanthophyll closer to the surface. But I would need to ask a specialist!

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