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  3. An Essential Scientific Process All l

An Essential Scientific Process All l

免费考试题库2019-12-17  34
问题 An Essential Scientific ProcessAll life on the earth depends upon green plants. Using sunlight, theplants produce their own food. Then animals feed upon the plants. They take inthe nutrients the plants have made  sted. But that’s not all.Sunlight also helps a plant produce oxygen. Some of the oxygen is used by theplant, but a plant usually produces me oxygen than it uses. The excess oxygenis necessary f animals  other ganisms to live.The process of changing light into food  oxygen is calledphotosynthesis. Besides light energy from the sun, plants also use water carbon dioxide. The water gets to the plant through its roots. The carbondioxide enters the leaves through tiny openings called stomata. The carbondioxide travels to chloplasts, special cells in the bodies of green plants.This is  photosynthesis takes place. Chloplasts contain the chlophyllsthat give plants their green col. The chlophylls are the molecules thattrap light energy. The trapped light energy changes water  carbon dioxide toproduce oxygen  a simple sugar called glucose.Carbon dioxide  oxygen move into  out of the stomata. Watervap also moves out of the stomata. Me than 90 percent of water a planttakes in through its roots escapes through the stomata. During the daytime, thestomata of most plants are open. This allows carbon dioxide to enter the leavesf photosynthesis. As night falls, carbon dioxide is not needed. The stomataof most plants close. Water loss stops.If photosynthesis ceased, there would be little food  other ganicmatter on the earth. Most ganisms would disappear. The earth’s atmospherewould no longer contain oxygen. Photosynthesis is essential f life on ourplanet.　　词汇：nutrient n.营养物 ganism n.生物体，有机体carbon dioxide n.二氧化碳chloplast n.叶绿体molecule n.分子vap n.水蒸气oxygen n.氧气 photosynthesis n.光合作用chlophyll n.叶绿素glucose n.葡萄糖cease v.停止　　注释：1.Then animals feed upon the plants.动物以植物为食。　　练习：5.Another good title f this passage would beA.Oxygen  Carbon Dioxide.B.Plants  Their Roots.C.How Photosynthesis Wks.D.Why Our Earth Needs Water.
选项
答案C
解析5.C　文章的主题是光合作用的基本原理，因此选项C。A、B项在文中有提及，但不是主旨，D项与本文无关
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