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  • 丙烯酸酯

    An illustration of a bacterium, highlighting its shape and molecular structure.

    What are the most numerous organisms on the planet?
    ::地球上数量最多的生物是什么?

    . And all it takes is one to quickly grow, under just the right conditions, into millions and billions. Luckily, we know how to control bacteria when necessary. But bacteria do serve many important purposes. In fact, we could not survive without them.
    ::。 只需要一个在适当条件下迅速成长到数以百万计的细菌。 幸运的是,我们知道如何在必要时控制细菌。 但是细菌确实能为许多重要目的服务。事实上,没有细菌,我们就无法生存。

    Evolution of Prokaryotes
    ::Prokaryotes的演变

    No doubt you’ve had a sore throat before, and you’ve probably eaten cheese or yogurt. If so, then you’ve encountered the fascinating world of prokaryotes. Prokaryotes are single-celled organisms that lack a . They also lack other membrane-bound . Prokaryotes are tiny and sometimes bothersome, but they are the most numerous organisms on Earth. Without them, the world would be a very different place. Prokaryotes are the simplest organisms. The first and organisms to evolve would be classified as prokaryotic.
    ::毫无疑问,你曾经有过喉咙痛,而且你可能吃过奶酪或酸奶。 如果是这样的话,那么你已经体验到了prokaryotes的迷人世界。 prokaryotes是缺乏一种单细胞生物。它们也缺少其他含膜生物。prokaryotes很小,有时也很麻烦,但它们是世界上数量最多的生物。没有它们,世界将是一个非常不同的地方。prokaryotes是最简单的生物。首先进化的生物和进化的生物将被归类为prokaytography。

    Prokaryotes are currently placed in two . A domain is the highest taxon , just above the . The prokaryote domains are Bacteria and (see Figure ). The third domain is Eukarya . It includes all eukaryotes . Unlike prokaryotes, eukaryotes have a nucleus in their cells.
    ::Prokaryotes目前被置于两个区域。一个域是最高分类符,仅高于该分类符。 prokaryote 域是细菌和(见图 ) 。第三个域是 Eukarya 。 它包括所有eukaryotes。 与 prokaryotes 不同的是, eukaryotes 在细胞中有一个核。

    A Venn diagram depicting the three domains of life: Bacteria, Archaea, and Eukarya.

    The Three Domains of Life. All living things are grouped in three domains. The domains Bacteria and Archaea consist of prokaryotes. The Eukarya domain consists of eukaryotes.
    ::生命的三大域。 所有生物都分为三个域。 细菌和Archaea 域由prokaryotes组成。 Eukarya 域由eukaryotes组成。

    It’s not clear how the three domains are related. Archaea were once thought to be offshoots of Bacteria that were adapted to extreme environments. For their part, Bacteria were considered to be ancestors of Eukarya. Scientists now know that Archaea share several traits with Eukarya that Bacteria do not share (see Table ). How can this be explained? One hypothesis is that Eukarya arose when an Archaean cell fused with a Bacterial cell. The two cells became the nucleus and cytoplasm of a new Eukaryan cell. How well does this hypothesis fit the evidence in Table ?
    ::不清楚这三大领域之间的关系。 Archaea曾经被认为是适应极端环境的细菌的产物。 而细菌则被认为是尤卡里亚的祖先。 科学家现在知道,Archaea与尤卡里亚有着细菌所不共有的若干特征(见表 ) 。 这如何解释呢? 一种假设是,当一个阿赫萨尼细胞与细菌细胞结合时,尤卡里亚就出现了。 这两个细胞成了新欧卡里亚细胞的核心和细胞。 这个假设与表里的证据有什么相配?

    Characteristic Bacteria Archaea Eukarya
    Flagella Unique to Bacteria Unique to Archaea Unique to Eukarya
    Unique to Bacteria Like Bacteria and Eukarya Unique to Eukarya
    Unique to Bacteria Like Eukarya Like Archaea
    Introns Absent in most Present Present
    Peptidoglycan (in cell wall) Present Absent in most Absent

    Summary
    ::摘要

    • Prokaryotes include Bacteria and Archaea. An individual prokaryote consists of a single cell without a nucleus.
      ::Prokaryotes包括细菌和Archaea, 单子血管由没有核的单细胞组成。
    • Bacteria live in virtually all environments on Earth.
      ::细菌几乎生活在地球上的所有环境中。
    • Archaea live everywhere on Earth, including extreme environments.
      ::Archaea生活在地球上的任何地方,包括极端环境。

    Review
    ::回顾

    1. What are prokaryotes?
      ::什么是prokaryoytes 是什么?
    2. What are two major differences between Bacteria and Archaea?
      ::细菌和Archaea之间的两大区别是什么?