Leaves are nature's food factories. Plants take water from the ground through their roots. They take a gas called carbon dioxide from the air. Plants use sunlight to turn water and carbon dioxide into oxygen and glucose(葡萄糖). Oxygen is a gas in the air that we need to breathe. Glucose is a kind of sugar. Plants use glucose as food for energy and as a building block for growing. The way plants turn water and carbon dioxide into sugar is called photosynthesis(光合作用).

　　A chemical called chlorophyll (叶绿素)helps make photosynthesis happen. Chlorophyll is what gives plants their green color.

　　As summer ends and autumn comes, the days get shorter and shorter. This is how the trees "know" to begin getting ready for winter.

　　During winter, there is not enough light or water for photosynthesis. The trees will rest, and live on the food they stored during summer. They begin to shut down their food-making factories. The green chlorophyll disappears from the leaves. As the bright green dies away, we begin to see yellow and orange colors. Small amounts of these colors have been in the leaves all along. We just can't see them in summer, because they are covered up by the green chlorophyll.

　　The bright reds and purples we see in leaves are made mostly in the fall. In some trees, like maples, glucose is trapped in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn cause the leaves to turn this glucose into a red color. The brown color of trees like oaks is made from wastes left in the leaves.

【广东省肇庆市2016-2017学年高一上学期期末质量检测英语试卷】相关文章：

★ 江西省景德镇市2017-2017学年高一上学期期中质量检测英语试题 Word版含答案

★ 广东省东莞市第七高级中学2017-2017学年高一上学期期中考试英语试题

★ 河北省邯郸市2017届高三上学期期末教学质量检测英语试卷

★ 广东省肇庆市2016-2017学年高一上学期期末考试英语试卷

★ 新疆兵团建工师第四中学2017-2017学年高一上学期期中考试英语试题（无答案）

★ 浙江省湖州市2016-2017学年高一上学期期中考试英语试卷

★ 浙江省杭州市重点中学2017-2017学年高一上学期抽测英语试题

★ 山西省原平市第一中学2016-2017学年高一上学期期中考试英语试题 Word版含答案

★ 河南省许昌市五校2017-2017学年高一上学期第二次联考英语试题 Word版无答案

★ 广东省广州英豪学校2014-2015学年高一上学期期中英语试卷