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Why Do Leaves Fall in Autumn?

– Houston, Texas
Fall, Autumn, leaves, science, nature, biology, photosynthesis, chlorophyll, cells, energy

The scene of leaves taking on a reddish-yellow hue and falling to the ground is a familiar one. Many people look forward to autumn because of its unique beautiful scenery. But what makes leaves change color and fall off of trees?


Changing Color

Leaves change color in the fall because they stop photosynthesis, which is the process of turning sunlight into the tree’s sustenance. The trees do not have enough sunlight or water to photosynthesize as days become shorter and the weather becomes colder, so they stop this process and live off of glucose stored from the summer. Stopping photosynthesis makes chlorophyll, the green pigment that helps them absorb sunlight, fade away which makes other colors like red, brown, or yellow more visible. These pigments are always present in the leaves, but they are usually hidden by the vibrant green color of chlorophyll.

Fall, Autumn, leaves, science, nature, biology, photosynthesis, chlorophyll, cells, energy

Falling off Trees

After leaves stop the process of photosynthesis and have lost their chlorophyll, they also lose their usefulness. The main purpose of leaves during spring and summer is to collect sun and produce food, so when this isn’t needed they die and fall off the trees. But rather than dying because they have stopped photosynthesis and lose energy, they die because the tree sheds them off purposefully. A special type of cell grows under the stem where the leaf is attached to its tree which eventually cuts off the connecting tissue. However, these cells have another purpose besides cutting off the leaf: They also must seal the place where the leaf was attached, leaving a leaf scar when the leaf blows off the tree. This process helps trees keep in more energy during winter time rather than losing energy on leaves that are no longer useful.


Learning about the science behind leaves in Fall is definitely interesting! Rather than leaves becoming a different color and dying because of the cold, they actually reveal pre-existing colors and are purposefully cut off to store energy. There are still many more discoveries to be made about the beauty of nature, just like how the trees reveal their beautiful colors to us, so as always stay curious!

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