字幕列表 影片播放 列印英文字幕 Hi guys! What's it like outside this time of year where you live? In our part of the world, the days are getting shorter, and the weather's getting cooler, and some of the leaves on the trees are starting to change colors. This might be happening where you live too — or it might be happening pretty soon. That's because we're heading into one of the most colorful times of year— autumn! Nothing says autumn or fall like lots of brightly colored leaves to rake and jump into, or just to pick up and admire. Now, some trees -- like pine trees, spruces and firs -- stay green all autumn and winter. But for many of the trees that have leaves, instead of pointy needles, this time of year means their leaves will turn different shades of red, orange, and yellow and eventually drop to the ground. Have you ever wondered why this happens? To find out, let's take a close look at a green leaf. Leaves on most plants and trees are green because of a colorful chemical inside them called chlorophyll. Chlorophyll is bright green. But it does more than just look pretty! It has a special job, because it's able to capture the energy that's in sunlight. Leaves use this light energy to make sugars, which the tree can then use for its own energy! So chlorophyll is what plants use to make their own food from sunlight! But! Chlorophyll isn't the only thing in tree leaves that gives them color. Leaves have lots of other colorful chemicals -- called pigments -- inside them, that are red, yellow, orange, and even purple. If you've eaten carrots, cabbage, or cherries, then you've not only seen these pigments, you've had them for lunch! All of these colorful pigments have special jobs, but only chlorophyll helps a plant make the sugar that it needs to live. And since chlorophyll's job is so important, there's way more of it in green leaves than any of the other pigments. In fact, there's so much chlorophyll that its green color covers up all of the other colors. Through spring and summer, we don't see the red, yellow, and orange pigments in the leaves—we just see the green chlorophyll. But as summer starts to turn into fall, and the days get shorter, less and less sunlight hits the tree's leaves ... ...so the tree starts to make less and less chlorophyll. Then the leaves become less green, and we're able to see more of the other colors that were there all along! And when that starts to happen, you might want to take the time to enjoy these pretty leaves while you can … because not long after they turn color, they begin to fall! They fall because, without their chlorophyll to help them make energy, the leaves don't really have a job to do. So as winter approaches, the energy that the leaves have made flows into the tree, and gets stashed away. Then, when the time is just right, they break off from the branches and fall to the ground. The tree can then live through the winter, using the energy that it's saved up, until the days start to get longer and warmer. Then it grows new leaves to capture the sunlight… ...and the cycle starts all over again. So when you start to see yellow, orange and red leaves showing up where you live, remember, those colors were there are all along -- -- Autumn is just their time to shine! Thanks for joining me on SciShow Kids. What's your favorite colored leaf? If you found an extra pretty one, get an adult to help you take a picture of it and send us an email at firstname.lastname@example.org! And we'll see you next time.