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  • 真核生物向多细胞生物的进化

    Depiction of Dickinsonia costata, an enigmatic organism from the Ediacara fauna.

     

    If you could go back to the late Precambrian, would you recognize these as ancestors of modern life?
    ::如果你能回到已故的普雷坎布里安 你会承认这些是现代生活的祖先吗?

    This is a depiction of  Dickinsonia costata , a member of the Ediacara fauna. No one knows quite how to categorize these organisms. Some scientists think that they are the ancestors of modern life. But most scientists believe that the Ediacara fauna died out and that other organisms were the ancestors of modern life. If you could go back in time maybe you could figure it out. But since that isn't possible, is there any way to really know?
    ::这是对Dickinsonia Costata的描述,Dickinsonia Costata是Ediacara动物群的成员。没有人知道如何分类这些生物体。有些科学家认为他们是现代生活的祖先。但大多数科学家认为Ediacara动物群是死亡的,而其他生物是现代生活的祖先。如果你能回到过去,也许你可以把它找出来。但是,既然这样不可能,有没有办法真正知道呢?

    Life Gets More Complex
    ::生活变得更复杂

    Eukaryotes  evolved about 2 billion years ago. Unlike  prokaryotes ,  eukaryotes  have a cell  nucleus . They have more structures and are better organized. Organelles within a eukaryote can perform certain functions. Some supply  energy ; some break down wastes. Eukaryotes were better able to live and so became the dominant life form. You can see an example of a eukaryotic cell below ( Figure   ).
    ::Eukaryotes在20亿年前就进化了。与prokaryotes不同,eukaryotes有一个细胞核。它们拥有更多的结构,并且组织得更好。eukaryotes内部的Organelles可以发挥某些功能。一些供应能源;一些分解废物。Eukaryotes更有能力生活,因此成为主要的生命形式。您可以看到下面的eukaryotes细胞的例子(图 )。

    An eukaryotic animal cell, highlighting various organelles and their functions.

     

    A eukaryotic cell. This one is from an animal.
    ::衣原体细胞,这个是动物产的

    Multicellular Life Originates
    ::多细胞生命来源

    For life to become even more complex, multicellular organisms needed to evolve. Prokaryotes and eukaryotes can be multicellular.
    ::要使生命变得更加复杂,多细胞生物就需要进化。 Prokaryotes和eukaryotes可以是多细胞。

    Toward the end of the Precambrian, the Ediacara fauna evolved ( Figure   ). The Ediacara fauna was extremely diverse. The organisms appeared after Earth defrosted from a worldwide glaciation. The Ediacara fauna seems to have died out without leaving descendants. Other multicellular organisms appeared in the Phanerozoic.
    ::在Precambrian的末端,Ediacara动物群进化(图 ) , Ediacara动物群极为多样化,在地球从全球冰川脱霜后出现生物体,Ediacara动物群似乎在未留下后代的情况下死亡,其他多细胞生物体出现在Phanerozoic。

    Fossil of an Ediacara organism, depicting ancient multicellular life from the Precambrian.

     

    A fossil of an Ediacara organism.
    ::一种Ediacara生物的化石

    Summary
    ::摘要

    • Eukaryotic cells have a nucleus. They also have well-developed structures.
      ::Eukaryaty细胞有一个核心,它们也有完善的结构。
    • Eukaryotes did not evolve until 2 billion years ago.
      ::Eukaryotes直到20亿年前才演变。
    • Ediacara organisms probably went extinct. Other organisms were the ancestors to modern life.
      ::Ediacara生物可能灭绝,其他生物是现代生命的祖先。

    Review
    ::回顾

    1. Describe eukaryotic cells.
      ::eukaryaty细胞描述。
    1. Why are organelles important to cells?
      ::为什么器官对细胞很重要?
    1. Describe the Ediacara fauna.
      ::描述Ediacara动物群。

    Explore More
    ::探索更多

    Use the resource below to answer the questions that follow.
    ::利用以下资源回答以下问题。

    1. What were the first life forms on Earth?
      ::地球上第一种生命形式是什么?
    1. What is the origin of multicellular organisms?
      ::多细胞生物的起源是什么?
    1. What three traits are needed for a group of cells to be considered a multicellular life form?
      ::要将一组细胞视为多细胞生命体,需要具备哪些三个特征?
    1. How many branches of complex organisms are there projected to be?
      ::预计会有多少个复杂的生物分支?
    1. What is the oldest multicellular life fossil found?
      ::发现的最古老的多细胞生命化石是什么?
    1. What is necessary for all life that we know of?
      ::我们所知道的所有生命需要什么?
    1. What do scientists look for when looking for life on Earth?
      ::科学家在寻找地球上的生命时寻找什么?
    1. What needed to happen for cells living in colonies to become multicellular organisms?
      ::生活在聚居区的细胞要成为多细胞生物,需要做些什么?