Why are trees green?


Today, we went for a stroll at Westonbirt Arboretum – a good opportunity to answer this question about why trees are green.

Trees and many other plants look green because their leaves and sometimes their stems contain a substance called chlorophyll. The word ‘chlorophyll’ comes from two Greek words that mean ‘green’ and ‘leaf’.

Chlorophyll is a really important molecule for plants because they use it to make their own food in a chemical reaction called photosynthesis. Photosynthesis uses energy from sunlight to convert water and carbon dioxide into a sugar called glucose, which plants use as food.

But why does chlorophyll make leaves look green?

Well, light from the Sun is a mixture of light of all colours of the rainbow. Chlorophyll absorbs red and blue light but not green light. So, when sunlight shines onto plants, the red and blue light is absorbed by the leaves but the green light is reflected back. Our eyes see this reflected green light, so plant leaves look green to us!

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