Prep2, essay #4

timetoleave

A recent experiment has supplied a more promising method for controlling the algae.  To repress the algae cells' capacity for accommodating themselves to environmental changes, the water in the solar pond was first made more saline through evaporation and then diluted by a rapid inflow of fresh water.  This shock reduced the cells' ability to regulate the movement of water through their membranes. They rapidly absorbed water, resulting in distortions of shape, increase in volume, and impairment to motility. Their buoyancy adversely affected, the cells sank to the bottom of the pond, where they encountered the hot waters of the storage layer and were destroyed. This method allows for effective control of nuisance algae while leaving solar ponds as one of the cleanest technologies providing energy for human use.

Question #15. 

 

Which of the following, if true, would seriously undermine the validity of the conclusions drawn from the experiment described in the last paragraph of the passage?

 

(A) The algae cells that sank to the bottom of the pond were destroyed only after a time lag of twenty-four hours.

(B) The lateral motility of the algae cells that sank to the bottom of the pond was not impaired.

(C) The water with which the artificial solar pond was diluted contained microorganisms that kill algae.

(D) The algae cells that sank to the bottom of the pond were actually killed by the rapid change in pressure.

(E) The higher salinity brought about through evaporation increased the transparency of the upper levels of water in the pond.

Why the key is C? I chose B... thanks!!!

youdoudou

up , 有xdjm能帮忙解释一些么？我也选b 好不容易查到这个贴还没人回。。。

b不是说杀不死么，那不就是weaken么？？

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scut_long

 B中，algae已经沉下去了，不影响上层水的透光性就行

C中，如果是其他方式杀死algae,那么第三段所说的迅速改变盐浓度来破坏algae的浮性使其沉下去这个过程就不会发生。就是说杀死后，那些algae还有可能是浮在上层水面，破坏透光性

emiliejiang

我在这道题目里纠结了很久，也看了别人的解答。但是都觉得不满意。我自己的结论是：这是一个实验，实验用的水里有“微生物”杀死了海藻，并没有证明实验本来要证明的pressure问题。也就是说这种方法是否可行根本不知道，因为也许下次inflow 的水没有微生物了。 其实就是一个实验没控制变量的flaw。