Question

Have you ever wondered how and why a fall leaf changes color? We first have to understand what leaves are and what they do.

Plants are the world’s food factories. Plants take water from the ground and take CO2 from the air. Plants use sunlight to turn water and CO2 into glucose(葡萄糖). Glucose is a kind of sugar. Using it as food, plants get energy and grow. Plants using sunlight to turn water and CO2 into sugar is called photosynthesis(光合作用). ChlorophyII helps photosynthesis. It 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 light or water for photosynthesis. 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 chlorophyII disappears from the leaves, we begin to see yellow and orange leaves. These colors have been in the leaves all the time. We just can’t see them in the summer, because they are covered up by the green chlorophyII.

The bright reds and purples we see in leaves are made mostly in autumn. In some trees, glucose is caught in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn turn this glucose into a red color. The brown color of trees is made from waste left in the leaves. It is mixture(混合物) of all these things. It makes the beautiful leaves during autumn.

根据材料内容选择最佳答案。

1.The underline word ＂chlorophyII＂ in the passage means ＂ ＂ in Chinese.

A. 胡萝卜素 B. 叶绿素 C. 氯霉素 D.花青素

2.When they rest in winter, trees live on the food they store during the .

A. summer B. autumn C. winter D. spring

3.Plants use sunlight to turn into sugar.

A. water and chlorophyII

B. water and CO2

C. CO2 and glucose

D. water and glucose

4.Which of the following is NOT true according to the passage?

A. Glucose is a kind of sugar and plants use it as food for energy and growing.

B. Leaves turn red because sunlight and the cool nights of autumn turn glucose into a red color.

C. We can’t see yellow or orange leaves in summer because the two colors are not in leaves.

D. During winter, there is not enough light or water for photosynthesis.

5. What’s the main meaning of this passage?

A. What’s photosynthesis?

B. How and why leaves change colors?

C. Different kinds of leaves.

D. How the seasons change.

Answer 1