[CASK EFFECT] 难度【LSAT】1-15 解读

lghscuUID: 2552043

题目请参考

【CASK EFFECT】0910G阅读全方位锻炼--难度【LSAT】1-15

【CASK EFFECT】1006G阅读全方位锻炼--难度【LSAT】--答题解读汇总

答案：BEECBA
16(B)
题目关键语句为“bacteria detect changes … in front and back of the cell body simultaneously”
查找相关信息如下
“the bacteria swim along a gradient of the attractant”
“their swimming pattern consists only of smooth runs and tumbles, the latter resulting in random changes in direction”
“As the bacteria encounter increasing concentrations of the attractant, their tendency to tumble is suppressed, whereas tumbling increases whenever they move away from the attractant”
以上信息表明bacteria根据substance梯度值决定smooth runs/tumbles，他们沿着梯度增大的方向行进以寻找attractant。如果梯度变化不大，通过tumbles产生新的寻找方向，然后再检测梯度变化，不断重复。这一过程算得上一个“寻食优化算法”
如果bacteria如题目所述那样检测，则
“If, on the other hand, bacteria detect a chemical gradient by measuring it simultaneously at two distinct points, front and back, on the cell body, they would not respond to the jump in concentration because the concentration of the attractant in front and back of the cells, though high, would be uniform”这里的jump指代内容为
“when suddenly exposed to a uniformly high concentration of an attractant”
很明显，虽然当前concentration比较高，但concentration为uniformly，因此，梯度为0。而exposed之前，concentration比较低，但同样为uniformly，即梯度也为0。“寻食优化算法”的重要参量“梯度”并没有变化，bacteria检测到的值也是相同的。因此，他们的行为并不会发生变化。只有选项(B)是这样描述的。
“When suddenly transferred from a medium in which the concentration of an attractant was uniformly low to one in which the concentration was uniformly high, the bacteria’s exhibited no change in the pattern of their motion”

17(E)
根据“a bacterium would increase the likelihood of its moving away from an area where the concentration of a harmful substance is high”定位原文
“They are attracted to materials they need and are repelled by harmful substances”
“As the bacteria encounter increasing concentrations of the attractant, their tendency to tumble is suppressed, whereas tumbling increases whenever they move away from the attractant”
注意到need—attracted, harmful—repelled，推断出二者相反。即高梯度应该tumbles，低梯度应该smooth runs
选项(E)表述最为恰当
“Exhibited an increased tendency to tumble as it encountered increasing concentrations of the substance, and suppressed tumbling as it detected decreases in the concentration of the substance”

18(E)
根据“swimming up a concentration gradient”定位原文
“when suddenly exposed to a uniformly high concentration of an attractant, the cells would behave as if they were swimming up a concentration gradient, with long, smooth runs and relatively few tumbles.”
再根据“with long, smooth runs and relatively few tumbles.”定位前文
“the bacteria swim along a gradient of the attractant, from an area where the concentration of the attractant is weaker to an area where it is stronger. As they do so, their swimming is characterized by a decrease in tumbling and an increase in straight runs over relatively longer distances.”
“with long, smooth runs and relatively few tumbles.”与“by a decrease in tumbling and an increase in straight runs over relatively longer distances.”表述相同动作，那么“swimming up a concentration gradient”也应该和“定位前文”中对应内容相同，即
选项(E)
“From an area where the concentration of a substance is weaker to an area where it is stronger”

19(C)
根据“the pattern that characterizes a bacterium’s motion changes in response to”结合第16题分析““the bacteria swim along a gradient of the attractant”
选项(C)“The bacterium’s detection of changes in the concentration of an attractant”为同意表述

20(B)
根据“the organization of the third paragraph of the passage”阅读第三段
“Biologists have proposed two mechanisms …First…Alternatively…the initial concentration”提出两种proposals
“Researchers reasoned …the cells would … If, on the other hand, … they would …”Researchers对两种情况的分析
“Experimental evidence suggests …”实验证实假设之一
选项(B)与(C)最为接近答案，但需要排除一个。
选项(C)中的“the flaws inherent in one of them are elaborated”明显不对，因为只提到一方面，而且还是错误的表述
再确定选项(B)
“a way of determining which of them is more likely to be true is discussed”这是专家“两种情况分析”的另一种说法，因此，(B)为最佳选项

21(A)
“The seemingly erratic motion exhibited by a microorganism can in fact reflect a mechanism by which it is able to control its movement”

Erratic motion并不erratic，因为“They are attracted to materials they need and are repelled by harmful substances.”

dave2008UID: 2489122

19题貌似不少人会选E，我做的时候也选了这个。。
说说我的理解吧，题目问的是in response to，也就是说运动方式的改变是以下哪一个选项的回应，这样理解的话应该就比较好选了
C：detection正是导致它变化的原因
E：这个是很具体，但说得却是变化的表现了，不符合题意