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Asked by jessicawilliams to Angela, Gabriele, Karen, Maria, Shane on 11 Nov 2013. This question was also asked by nicolej.
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Karen McCarthy answered on 11 Nov 2013:
Leaves are green because of chlorophyll inside them, which reflects out green wavelengths of sunlight. As days get shorter, like in Autumn, there is less sunlight, so the chlorophyll begins to break down. Increases in sugars and chemicals called cartenoids (what makes carrots orange!) begin to build up in the leaves then, which have distinctive red, orange and yellow colours!
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Shane Mc Guinness answered on 11 Nov 2013:
Yep, that’s it! Evergreen trees can maintain their chlorophyll by storing energy in their leaves to stop the chlorophyll from breaking down due to cold weather and a lack of light. They also have waxy leaves to prevent them from drying out. But this is expensive to produce for plants so in colder climates (like Ireland) it makes more sense to produce lots of cheap but weak leaves instead of spending all that hard-earned energy on complicated armour!
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Angela Stevenson answered on 11 Nov 2013:
Yes, it’s all about the chlorophyll and some chemical reactions taking place in the leaf. Basically, light regulates chlorophyll production. When autumn days grow shorter less chlorophyll is produced in the leaves so their green color starts to fade away. At the same time, surging sugar concentrations cause increased production of other pigments. For this reason, some leaves will appear red, others can be orange, or yellow.
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