欢迎来到上海新航道官网!英语高能高分,就上新航道!

4008-125-888

首页>sat>阅读>正文

sat阅读真题+答案+解析

2017年12月12日 03:04来源:互联网作者:上海管理员

摘要:题目:Plants, and all other living things, require nitrogen for growth; it is an essential component ofnucleic acids and proteins. Although air is mostly nitrogen, this gaseous form is inaccessible toplants and must be fixed into ammonium to render it biolog

今天上海新航道 小编为大家带来的是关于sat阅读的真题,本题是一道批判思维的选这题。

题目:

Plants, and all other living things, require nitrogen for growth; it is an essential component ofnucleic acids and proteins. Although air is mostly nitrogen, this gaseous form is inaccessible toplants and must be fixed into ammonium to render it biologically relevant. Soil bacteria calledrhizobia fix nitrogen, but to do this they must first take up residence inside the roots oflegumes like pea, alfalfa, clover, and soybean.

Soon after a legume begins to grow, rhizobia invade its root hairs and multiply, causing theplant to form specialized organs—nodules—that contain the proliferating bacteria. Thissymbiotic arrangement benefits both parties: legumes can thrive without nitrogen fertilizersonly if they have functional nitrogen-fixing nodules, while the bacteria receive the energyneeded to multiply and fix nitrogen from the plant. When the plant dies, the fixed nitrogen isreleased into the soil so other plants can use it. This process has significant implications foragriculture, as nitrogen is the most common nutrient deficient in the earth’s soil and, thus,the one most commonly supplied by chemical fertilizers.

Rhizobia are a diverse group taxonomically, genetically, and metabolically. They can be foundin distant genera. Their symbiotic trait appears to have arisen independently multiple times byhorizontal transfer of genes. However, it is not thought that this horizontal gene transferis sufficient to confer symbiosis, or to explain the biodiversity of rhizobia. There must beselective pressures preventing or permitting the expression of the acquired symbiosis trait andadaptive mechanisms to deal with these pressures. But neither the pressures nor themeasures taken to circumvent them are known.

What can reasonably be inferred about the fixed nitrogen released when a plant dies?

A.It is biologically insignificant because it reverts to its gaseous form.

B.It is not sufficient to maintain adequate nitrogen levels in soil.

C.It is less useful for other plants than the nitrogen found in chemical fertilizers.

D.It is not a consideration in farmers' decisions regarding agricultural practices.

上海新航道SAT培训班

答案:B

解析:

Choice B is the best answer. The author states that soil commonly is nitrogen-deficient andthat nitrogen is often supplied by fertilizers, even though the fixed nitrogen released whenlegume plants with nitrogen-fixing nodules die can be used by other plants. This suggests thatthe fixed nitrogen those legume plants release is not enough to supply all of the nitrogen thatis needed in soil; fertilizers are needed to address the remaining nitrogen deficiency.

上海sat'培训班

上海sat'培训班

上海sat'培训班

请加sunny老师(微信号:shnc2014

百人留学备考群,名师答疑,助教监督,分享最新资讯,领取独家资料。扫码免费加入

免费资料领取

热报课程

  • SAT系列课程
课程名称 班级人数 课时 学费 报名
SAT基础精讲班(争1250+分) 15-20人 72课时 ¥16800元 在线咨询
SAT精品强化班(争1350+分) 15-20人 72课时 ¥16800元 在线咨询
SAT精英冲刺班(争1500+,VIP铂金班) 3-6人 36课时 ¥16800元 在线咨询
SAT香港/美国考试团 99 3-8天 ¥6000-28800 在线咨询
SAT模考讲评班 15 6 ¥1280 在线咨询

免责声明
1、如转载本网原创文章,请表明出处;
2、本网转载媒体稿件旨在传播更多有益信息,并不代表同意该观点,本网不承担稿件侵权行为的连带责任;
3、如本网转载稿、资料分享涉及版权等问题,请作者见稿后速与新航道联系(电话:021-64380066),我们会第一时间删除。

免费在线模考测试

姓名:

电话:

立即测试

制作:每每

旗舰校区:上海市徐汇区裕德路126号
电话:4008-125-888 传真:+021-61208858
版权所有:新航道(北京)管理咨询有限公司 京IPC备05069206