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21英语教师网 > 备课资源 > 拓展阅读 > 正文
The trees in color
作者:21ST    来源:21英语网    日期: 2012-12-17

外研版初二年级:The trees in color

关键词:The wettest place

话题归类:天气Weather

 

是谁让这个季节变得如此的绚烂多彩?


全版词数 500 建议阅读时间 14分钟 教案见网站

DID you enjoy autumn? Yellow, orange, red and purple! Why do the leaves change their colors every fall? It is a mysterious (神秘的) thing and scientists are still trying to work out what exactly happens.

Inside a leaf, there are millions of little color "bags". They're green, yellow and orange. The green ones are chlorophyll (叶绿素). The yellow ones are xanthophylls (叶黄素). The orange ones are carotene (胡萝卜素).

Trees are busy in summer. They make lots of food and store it for winter. The chlorophyll has the job of making food. It catches sunlight to change water and carbon dioxide (二氧化碳) into sugar. This sugar is the food for the tree. There is a lot of chlorophyll and it is busy working. It covers up all of the other colors in the leaf so the leaves look green.

When there is less light in autumn, there is less chlorophyll. This is because chlorophyll needs light to reproduce. The chlorophyll starts to break down or move to tree trunks. The other colors in the leaf come out. So the leaves don't really "turn" a certain color- they just lose their greenness.

But how about the red and purple leaves? As the weather becomes colder more sugar stays in the leaves. This makes the leaf look red and purple.



关键词:外研版初二年级 The weather 天气Weather



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