题目内容
Do you want to know how and why a fall leaf changes color? We first have to understand what leaves are and what they do.
Leaves are the world's food factories. Plants take water from the ground through their roots and take CO2 from the air. Plants use sunlight to turn water and CO2 into glucose(葡萄糖), a kind of sugar. Plants use it as food for energy and growing.
A chemical called “chlorophyll” in the leaves gives plants their green color. As summer ends and autumn comes, the days get shorter and shorter, and trees “know” to begin getting ready for winter.
During winter, there is not enough sunlight or water. Trees rest during this time and live on the food they store during the summer. They begin to shut down their food?making factories. As the green chlorophyll disappears from the leaves, we begin to see yellow and orange leaves.
The bright reds and purples we see in leaves are made mostly in autumn. In some trees, like maples(枫树), sunlight and the cool nights of autumn turn the glucose in the leaves into a red color. And we can enjoy the beautiful red leaves during autumn.
1.Which should be in the box?
sunlight＋
＋CO2→glucose
A. air B. sugar C. water
2.The underlined word “chlorophyll” means “ ”．
A. 蛋白质 B. 脂肪 C. 叶绿素
3.The leaves turn yellow because they are short of .
A. sunlight and water
B. glucose and energy
C. water and CO2
4.Which of the following is NOT true?
A. When autumn comes, the days get shorter and shorter.
B. Trees begin to stop making food in summer.
C. During winter some of the yellow and orange colors are still in the leaves.
