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Why do Leaves Change Colour?

Biology | 7-14 yrs | Learning Pod

Why do Leaves change color in the Fall?

  • There are two types of trees – evergreen and deciduous.
  • The evergreen trees do not shed their leaves. The deciduous trees shed their leaves every autumn.
  • As the winter season approaches, the days get shorter and cooler.
  • A tree’s sturdy trunk, branches and roots can survive in low temperatures, but the leaves are not so tough.
  • Also, there is little sunlight available for the leaves to make food and generate enough energy for the entire tree.
  • The freezing temperatures make water transport from the roots to the trunk and the trunk to the branches and leaves very difficult. If the leaves are allowed to stay during the winters, whatever moisture is left in the tree may get robbed by the harsh and cold winds via the surface of the leaves. So, the deciduous trees shut down their ‘leafy food factories’ in the winters to save their energy and go dormant.
  • In order to drop their leaves, deciduous trees start withdrawing pigments like chlorophyll from their leaves, which makes them change colour- from green to yellow and then brown.. Then, a thin layer of dead cells is formed at the base of the stem, which slowly detaches the leaf from the stalk.
  • The spots where the leaves were attached get carefully sealed. Now, no loss of water can happen. By the end of the autumn season, all the leaves fall. When spring brings warm air and fresh water, new leaves start sprouting again.

Why don’t Evergreens lose their Leaves?

Evergreen trees like pines, spruces, firs and cedars do not drop their leaves because they have thin needle-like leaves that are covered with a heavy wax coating. So, there is only a little surface area available from which the water can be lost. And, the fluids inside the cells of evergreen trees contain substances that are resistant to freezing.

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