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The secret of the falling leaves

Posted by Elsa Viegas on

Autumn is upon us; the days are starting to get shorter and colder while our little ones are becoming increasingly more curious. Why isn’t that tree green anymore? Why are its leaves falling off? Some deciduous trees are losing their green colour and their leaves are turning red and, of course, children want to know why.

 Leaves falling off trees

Yes, deciduous trees will soon have transformed into a display of ochres and reds almost on a par with the sunsets which are happening earlier each day. When Winter arrives, pathways will be covered in a thick, crunchy carpet which will leave the trees standing bare and the children stunned. But why do leaves fall off? Well, the leaves on deciduous trees fall in Winter because they stop being useful. Leaves are food factories for the rest of the plant, as they use energy from sunlight to transform carbon dioxide, water and other nutrients from the soil into the molecules that they need in order to grow and perform their vital functions: the famous photosynthesis. This process works very well when the weather is mild, but when it gets cold the leaves are a nuisance. They can’t do their job and so the plant gets rid of them.

 autumn tree

Frosty temperatures, for example, ruin leaves because the water they contain freezes, and this damages their tissues. Also, when the ground is frozen, roots cannot absorb water or nutrients as they can only do this if they are unfrozen. As a result, the plant dies of thirst by losing water through its leaves (as part of the photosynthesis process) and not being able to replace it through its roots.

 Autumn leaves 

And what about this bright orange colour? To avoid this death, when it starts to get cold the tree cuts off the supply of sap to the leaves, removes the chlorophyll and other elements, storing them in other tissues so it can make use of them when Spring comes around. Chlorophyll is a crucial chemical compound for harnessing the energy from the sun, and it is the pigment which gives leaves their characteristic green colour. As the leaf loses its chlorophyll, other underlying colours begin to appear. And voilà! that’s where the autumnal colours come from.

And you? Did you already know why leaves fall off trees? What other interesting questions does your little one ask? We’d love to read all about them.

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