Article #12 – Nature

Why Autumn Leaves Turn Orange?

Even though autumn is often called the season of ‘fall’, a lot of people actually welcome it as a much needed relief from those terribly scorching, hot summer months! When autumn is around the corner, you can breathe a sigh of relief that summer is indeed over for good! If you are from New England you should know how many tourists hop on to that area to catch a glimpse of the changing colors of leaves in this season. But the million dollar question remains: why do these leaves change colors from green to red, yellow and orange during this time? In this article I will answer just that!

Do you know how plants eat? Yes, they do eat indeed, but unlike us they can make their own food. All the while they grow, they produce a green pigment known as chlorophyll which helps (with the aid of sunlight) the plant convert water and carbon dioxide into its food, carbohydrates. For this reason, although a typical plant is multi-colored, the green chlorophyll pigment becomes the dominant color throughout its growing season. That is why plants remain green all through the growing season. When the season of fall comes, production of this chlorophyll is stopped dead in its tracks; in case of certain plants, the chlorophyll pigment present in the plant’s leaves start getting thinned out. Now that the dominant green pigment color is gone, the other colors of the plant (which were, as a matter of fact, always present there but in a form that was invisible to our eyes) such as red, orange and yellow start showing up! Those other colors belong to the other pigments which plants produce, such as xanthophylls and carotenes.

Production of the chlorophyll pigment is heavily dependent on the metabolic activity of a plant, which in turn is dependent on weather conditions. If the weather is not favorable then the production of chlorophyll either gets reduced or stopped completely. In this context, any level of temperature, sunlight, oxygen and water that is unsuitable for the production of chlorophyll can be termed as unfavorable weather condition. Grow a plant inside your home and its leaves would soon turn either yellow or show a waned green hue; this is because the plant is not getting enough sunlight, nitrogen, iron etc., something which would not have happened had it been allowed to grow up in the open. When a plant receives an excessive amount of heat or water (humidity), or when the temperature becomes cooler, then the production of chlorophyll stops and the green pigment is taken over by the yellow and orange pigments of xanthophylls and carotenes. All this while, the stock of carbohydrates which is the primary source of food for the plant also starts producing a molecule called anthocyanin, which in turn produces other pigment colors such as purple, pink and red; note that not all plants produce anthocyanin at the time of fall.

Well I hope that in this article I have been successful at explaining why leaves change their colors and turn orange during autumn.

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