GRE阅读练习每日一篇(四十一)_GRE阅读

GRE阅读练习每日一篇(四十一)

　　编辑点评： GRE阅读的方法相信大家已经积累了很多了，本文就为大家提供一些GRE阅读的材料，大家来练一练，把平时学到的东西运用到实际中，也多多积累词汇和句子，提高自己的阅读能力。

　　每天做一些标准的GRE阅读练习，有助于大家在GRE考试的复习过程中不断地进行练习和总结。希望大家在进行GRE阅读练习时，充分运用平时所积累的知识，这样才能有效果。

　　The deep sea typically has a sparse fauna dominated by tiny worms and crustaceans, with an even sparser distribution of larger animals. However, near hydrothermal vents, areas of the ocean where warm water emerges from subterranean sources, live remarkable densities of huge clams, blind crabs, and fish.

　　Most deep-sea faunas rely for food on particulate matter , ultimately derived from photosynthesis, falling from above. The food supplies necessary to sustain the large vent communities, however, must be many times the ordinary fallout. The first reports describing vent faunas proposed two possible sources of nutrition: bacterial chemosynthesis, production of food by bacteria using energy derived from chemical changes, and advection, the drifting of food materials from surrounding regions. Later, evidence in support of the idea of intense local chemosynthesis was accumulated: hydrogen sulfide was found in vent water; many vent-site bacteria were found to be capable of chemosynthesis; and extremely large concentrations of bacteria were found in samples of vent water thought to be pure. This final observation seemed decisive. If such astonishing concentrations of bacteria were typical of vent outflow, then food within the vent would dwarf any contribution from advection. Hence, the widely quoted conclusion was reached that bacterial chemosynthesis provides the foundation for hydrothermal-vent food chains an exciting prospect because no other communities on Earth are independent of photosynthesis.