Have you ever noticed how leaves change color in the fall? It’s like magic! One moment they’re green, and the next, they’re a beautiful mix of yellow, orange, red, and brown. But why does this happen? Let’s find out!
Leaves start out green because they have something called chlorophyll. Chlorophyll is a special substance that helps leaves make food for the tree using sunlight. But when fall comes, the days get shorter, and there’s less sunlight. The trees start to get ready for winter.
In the fall, trees do something really smart. They start to save up nutrients from the chlorophyll. These nutrients are like vitamins for the tree, and they are stored in the tree’s branches and trunk. This way, the tree can use them again when spring arrives and it’s time to grow new leaves.
When the chlorophyll is taken away, the green color fades. But leaves have other colors hiding inside them! These are yellow, orange, brown, and sometimes even red. So when the green fades, we get to see these beautiful colors that were there all along.
Some people might think that when leaves change color, the tree is sick or dying. But that’s not true! It’s just the tree’s way of getting ready for winter and making sure it has enough nutrients to grow new leaves in the spring.
Isn’t it amazing how trees have their own way of preparing for the seasons? There are so many mysteries in nature, and asking questions helps us learn more about the world around us. So keep wondering and exploring!
Thanks for joining us on this colorful journey. Remember, there are always new things to discover, so stay curious and keep asking questions!
Sure! Here’s a sanitized version of the transcript:
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[PHONE RINGING][DING] Whoo! Fall! I love fall. One of my favorite things to do is to rake up a big pile of leaves and then run and jump in them. Someone named Nikhil has a question about leaves. Let’s give him a call now. [PHONE RINGING][DING] Hi, Doug. Hi, Nikhil. I have a question for you. Why do leaves change color in the fall? That’s a great question. You’ve probably noticed leaves changing color in the fall, and they can be so pretty with all those different colors—yellow, orange, red. But why do they do this?
Leaves start out green, and then in the fall, or autumn, they turn different colors. What do you think? Why do you think leaves change color in the fall? Now would be a good time to pause the video and discuss. OK, you ready? I don’t know what ideas you might have come up with, but think about this: If you’ve ever forgotten to water a plant, you might have seen its leaves turn kind of yellow or brown. The plant is dying. Could it be that trees’ leaves are changing color because the trees are dying?
Well, it might look like the trees are dying. In fact, by the end of fall, the leaves actually fall off the tree. We think that might even be why we call this season fall. But think about it. A few months later, after winter has passed, springtime comes around, right? In spring, trees grow back new leaves, and they look healthy again. So when a tree’s leaves change color, that probably doesn’t mean it’s dying or sick.
Why would leaves change color in the fall, then? Now, I have to tell you, this is a question that is not easy to answer. It took scientists hundreds of years to figure it out. It was a real puzzle. First, using microscopes and other tools, scientists discovered that leaves contain a green-colored substance called chlorophyll. This is actually why leaves look green.
But now here was the really hard part to figure out: Why do leaves stop looking green in the fall? One clue scientists discovered is that in the springtime, when a tree is growing new leaves, it has to do a lot of hard work to make chlorophyll. Chlorophyll contains special nutrients that the tree pulls from the soil around it. That’s when scientists realized that every fall, if a tree were to drop its leaves while they’re still green, it would lose all the special nutrients that it used to make the chlorophyll.
So instead of losing the leaves when they’re green, trees have a way of saving some of those special nutrients. Here’s what they do: Before its leaves fall off, trees pull some of the nutrients from the green chlorophyll into their branches and trunks, places where the nutrients can be stored safely during the cold winter. So you see, that’s why the leaves stop looking green in the fall. The green stuff, chlorophyll, is getting taken apart and moved out of the leaves.
Now, that might make you think that in the fall, the leaves should look clear-colored, then, once there’s no chlorophyll left in them. But it turns out that chlorophyll isn’t the only colored substance in the leaves. Leaves also have substances inside them that can be yellow-colored, or in some leaves, orange-colored, or brown-colored, or in special cases, even red-colored.
So when trees pull some of the chlorophyll nutrients into their trunks and branches each fall, we begin to see some of the other colored substances in the leaves—browns, yellows, oranges, or reds that are left behind. That’s why leaves change color in the fall.
So in summary, when leaves change color in the fall, it doesn’t mean trees are dying or sick. It took scientists a long time to figure it out, but they discovered that in fall, trees are pulling nutrients from the green chlorophyll in their leaves to store them for winter. Then, in the springtime, trees reuse those nutrients to grow a new set of green leaves.
That’s all for this week’s question. Thanks, Nikhil, for asking it. Now, for the next episode, I reached into my question jar and found three questions submitted to me that I’m thinking about answering. When this video is done playing, you’ll get to vote on one. You can choose from: how do people make mirrors? Why do different places have different times? Or why does it rain so much in the rainforest? So submit your vote when the video is over. I want to hear from all of you watching. There are mysteries all around us. Stay curious, and see you next week.
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