The passage supports which of the following inferences about heterocysts?答案解析-雷哥GRE

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Researchers are finding that in many ways an individual bacterium is more analogous to a component cell of a multicellular organism than it is to a free-living, autonomous organism. Anabaena, a freshwater bacteria, is a case in point. Among photosynthetic bacteria, Anabaena is unusual: it is capable of both photosynthesis and nitrogen fixation. Within a single cell, these two biochemical processes are incompatible: oxygen produced during photosynthesis, inactivates the nitrogenase required for nitrogen fixation. In Anabaena communities, however, these processes can coexist. When fixed nitrogen compounds are abundant, Anabaena is strictly photosynthetic and its cells are all alike. When nitrogen levels are low, however, specialized cells called heterocysts are produced which lack chlorophyll (necessary for photosynthesis) but which can fix nitrogen by converting nitrogen gas into a usable form. Submicroscopic channels develop which connect the heterocyst cells with the photosynthetic ones and which are used for transferring cellular products between the two kinds of Anabaena cells.

The passage supports which of the following inferences about heterocysts?

Heterocysts do not produce oxygen. Nitrogen gas inactivates heterocysts. Chlorophyll increases the productivity of heterocysts. Heterocysts allow nitrogen fixation and photosynthesis to occur in the same cell. Heterocysts are more important for Anabaena’s functioning than are photosynthetic cells.

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4楼 | 2020-11-05 18:49:49 回复

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Researchers are finding that in many ways an individual bacterium is more analogous to a component cell of a multicellular organism than it is to a free-living, autonomous organism. 研究人员发现啊，在许多方面，individual bacterium，相较于自治有机体，与多细胞有机体更像。 Anabaena, a freshwater bacteria, is a case in point. anabaena就是个例子。 Among photosynthetic bacteria, Anabaena is unusual: it is capable of both photosynthesis and nitrogen fixation. 在光合作用的细菌中，anabaena是不同的: 他可以既光合又固氮。 Within a single cell, these two biochemical processes are incompatible: oxygen produced during photosynthesis, inactivates the nitrogenase required for nitrogen fixation. 单细胞里，这两种过程无法兼容：氧气通过光合作用产生，抑制了固氮所需的nitrogenase。 In Anabaena communities, however, these processes can coexist. 在anabaena中，却是可以共存的 When fixed nitrogen compounds are abundant, Anabaena is strictly photosynthetic and its cells are all alike. 当固氮混合物多的时候，anabaena抑制光合并且所有细胞相似。 When nitrogen levels are low, however, specialized cells called heterocysts are produced which lack chlorophyll (necessary for photosynthesis) but which can fix nitrogen by converting nitrogen gas into a usable form. 当氮的含量降低，一个专门的细胞，heterocysts，被产生，chlorophyll降低（光合作用的），heterocysts可以使气态氮转化为可用氮。 Submicroscopic channels develop which connect the heterocyst cells with the photosynthetic ones and which are used for transferring cellular products between the two kinds of Anabaena cells. 亚微观渠道连接了heterocyst和光合作用的细胞，并且帮助两种anabaena细胞之间传递物质

3楼 | 2020-08-08 02:17:31 回复

BarryChen

When nitrogen levels are low, however, specialized cells called heterocysts are produced。然而当氮的水平较低的时候，会产生一种叫做heterocysts的专门细胞。疑问，这难道不是说明，氮会抑制heterocysts的生成嘛？

2楼 | 2018-08-14 15:52:04 回复

863366vdhdc 回复 863366vdhdc 哈哈哈

2019-09-14 12:27:44 回复
320480zm 回复 320480zm 我猜nitrogen levels指的是前文提到的 nitrogen compounds，中文意思氮化合物。因此B选项的氮气显然不对了

2019-12-21 10:42:50 回复
WJLOGWHEN 回复 WJLOGWHEN 这是说heterocysts会在低氮的时候生成，并没有说氮会抑制heterocysts生成

2020-02-25 07:34:18 回复
296763rkmmh 回复 296763rkmmh 同感啊

2020-03-17 14:52:48 回复

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1楼 | 2018-05-03 17:38:25 回复

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