Yesterday my son and I were walking in Hyde Park’s glorious foliage, crunching the leaves and shooting them to sky, as all 4 year old and their adult mothers do. Suddenly my son stopped and said Mum, why are these leaves Lellow (meaning Yellow)? Like any other panic stricken adult that does not really know the answer to a 4 year olds question, I came up with a story about the trees needing to sleep for winter, followed by distraction tactic in the form of running to the Park’s shop and getting him a hot chocolate!
Later on last night, I set out to find the reasons in the simplest way for him. After some Googleing and documentaries I found out that the yellow colour is in the leaves all around the year, only that it is overpowered by the Green in summer and spring. This is how it happens:
Each leaf on a tree is like a tiny solar panel, gathering sunlight the tree uses to make food. Sunlight helps turn water and carbon dioxide into oxygen and glucose, a sugar that the tree uses for food (energy) to grow. This process of converting water and carbon dioxide into oxygen and glucose is called “photosynthesis.” Chlorophyll is the main chemical behind photosynthesis and gives plants their green color.
During winter, there is not enough light or water for photosynthesis. The trees will rest, and live off the food they stored during the summer. They begin to shut down their food-making factories. The green chlorophyll disappears from the leaves. As the bright green fades away we begin to see yellow and orange colours, small amounts of which have been in the leaves all along; we just can’t see them in the summer because they are covered up by the green chlorophyll.
The bright reds and purples we see in leaves are made mostly in the fall. In some trees, like maples, glucose is trapped in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn cause the leaves turn this glucose into a red colour. The brown colour of trees like oaks is made from wastes left in the leaves.
Armed with the correct and simple answer, I will be taking him back to the Park for some more leave crunching!
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