介绍:
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. Leaves have lots of other colorful chemicals - called pigments - inside them, that are red, yellow, orange, and even purple.
So 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 the 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.
大多数植物和树上的叶子成绿色是因为它们内部有一种叫叶绿素的彩色化学物质。叶绿素是鲜亮的绿色，但它不仅仅是看起来漂亮。它还有一种特殊的功能，能够吸收阳光中的能量。叶子利用太阳能转化生成糖类物质，然后树木可以利用这些糖类物质，然后树木可以利用这些糖类物质为自己提供能量。叶子里面还有很多其他颜色的化学物质，叫做色素，有红色、黄色、橙色，甚至是紫色。
所以在春季和夏季，我们看不到树叶上的红色、黄色和橙色色素。我们只能看到绿色色素。但从夏季开始进入秋季后，白天变短，照到树叶上的阳光越来越少，树木产生的叶绿素也越来越少，然后叶子的绿色减少，我们就能看到一直存在的其他颜色了。
