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An Essential Scientific Process All l

恬恬2019-12-17  37
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：1.In the first paragraph，the wd “excess” meansA.heavy.B.extra.C.green.D.liquid.
选项
答案B
解析1.B　前文讲到，植物产生的氧气一部分被植物自身消耗了，但植物消耗的氧气量远小于它们产生的氧气，因此可以推测这句话的意思应该是剩余的氧气对于动物以及其他生物体的生存是至关重要的。excess在句中的意思是“超额的”，与extra“额外的”意思相近。
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