[Small bite] Why are leaves green?

Occasionally, we post ‘small bites’. In this feature, we give brief answers to general scientific questions. This time it is all about leaves. Why are they green and how come they change colour in the autumn?

Plants do not eat, but make their own energy with sunlight, water, and carbon dioxide from the air. The energy factories responsible for this are located in the leaves and are called chloroplasts. These chloroplasts are responsible for the green colour as they absorb all visible colours from sunlight except green. The green colour they reflect back for us to see.

In the autumn, leaves die. To preserve the energy factories, the tree moves the chloroplasts from the leaves to the branches. We then see the coloured substances, the pigment, that leaves make themselves and are always present: red, orange and yellow. The colour differs per tree species, but also depends on the weather and where the tree grows.

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