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  • 细胞分裂

    A rusty old car parked behind a wooden fence, symbolizing worn-out cells.

     

    Do  cells  get worn out?
    ::细胞破损了吗?

    Yes, just like this car, cells cannot last forever. Cells do eventually wear out. At that point, they need to be replaced. This is one reason that your cells divide. New cells that result after cells divide are also used for growth and to repair cuts.
    ::是的, 就像这辆车一样, 细胞不能永远持续。 细胞最终会耗尽。 在这一点上, 它们需要被替换 。 这是您细胞分裂的原因之一。 细胞分裂后产生的新细胞也被用于生长和修补伤口 。

    Why Cells Divide
    ::为何分裂单元格

    Imagine the first stages of life. In humans and other  animals , a   fertilizes an  egg , forming the  . But humans are made up of trillions of cells, so where do the new cells come from? Remember that according to the  ,  all cells come from existing cells. Once a sperm and egg cell unite and the first cell, called a  zygote ,  forms, an entire baby will develop. And each cell in that baby will be genetically identical, meaning that each cell will have exactly the same  .
    ::想象生命的最初阶段。 在人类和其他动物中, 卵会受精, 形成。 但是人类是由数万亿个细胞组成的, 所以新细胞从何而来? 记住, 根据这些细胞, 所有细胞都来自现有的细胞。 一旦精子和蛋细胞联合起来, 第一个细胞, 叫做zygote, 形态, 整个婴儿就会发育。 婴儿中的每个细胞在基因上都是相同的, 这意味着每个细胞都有完全相同的细胞。

    How does a new life go from one cell to so many? The cell divides in half, creating two cells. Then those two cells divide, for a total of four cells. The new cells continue to divide and divide. One cell becomes two, then four, then eight, and so on ( Figure   ). This continual process of a cell dividing and creating two new cells is known as  cell division.  Cell division is part of a cycle of cellular growth and division known as the cell cycle—cells must grow before they divide. The   describes the "life" of a  eukaryotic cell . In addition to cell division, the cell cycle includes the division of the   and the  cytoplasm . 
    ::新的生命是如何从一个细胞分裂成这么多的? 细胞分裂成两半, 产生两个细胞。 然后这两个细胞分裂, 共四个细胞。 新的细胞继续分裂和分裂。 一个细胞分裂成两个细胞, 然后是四个, 然后是八个, 等等( 图表 ) 。 这个细胞分裂和创造两个新细胞的连续过程被称为细胞分裂。 细胞分裂是细胞生长循环的一部分, 分裂是细胞循环的一部分, 细胞在分裂之前必须成长。 描述一个电子细胞的“ 生命 ” 。 除了细胞分裂之外, 细胞循环还包括细胞分裂和细胞分裂。

    Most cell division produces genetically identical cells, meaning they have the same DNA. The process of  ,  which specifically is the division of the nucleus, ensures that each cell has the same DNA. During mitosis, the  chromosomes  equally separate, thus making sure each nucleus in each resulting cell after cell division is genetically identical.
    ::大部分细胞分解产生基因相同的细胞,意思是它们有相同的DNA。 具体地说,这是核的分解,它的过程确保每个细胞都有相同的DNA。 在细胞分解过程中,染色体同样分开,从而确保细胞分解后的每个细胞中的每个核在基因上是相同的。

    A special form of cell division, called  ,  produces cells with half as much DNA as the  parent cell . These cells are used for  . 
    ::一种特殊的细胞分解形式,叫做 , 产生细胞, 其DNA量为母细胞的一半。 这些细胞用于 。

    Stages of cell division, illustrating zygote dividing into multiple cells in sequence.

     

    Cells divide repeatedly to produce an embryo. Previously the one-celled zygote (the first cell of a new organism) divided to make two cells (a). Each of the two cells divides to yield four cells (b), then the four cells divide to make eight cells (c), and so on. Through cell division, an entire embryo forms from one initial cell.
    ::以前,单细胞的zygote(新生物体的第一个细胞)分裂成两个细胞(a),两个细胞的每一个分裂成四个细胞(b),四个细胞分裂成八个细胞(c),等等。通过细胞分裂,一个最初的细胞形成一个完整的胚胎。

    Besides the development of a baby, there are many other reasons that cell division is necessary for life:
    ::除了婴儿的发育之外,还有许多其他原因,即细胞分裂是生命所必需的:

    1. To grow and develop, you must form new cells. Imagine how often your cells must divide during a growth spurt. Growing just an inch requires countless cell divisions. Your body must produce new  bone  cells, new skin cells, new cells in your   and so on.
      ::为了成长和发展, 您必须形成新的细胞。 想象一下您的细胞在成长过程中必须分化的频率。 仅仅生长一英寸需要无数的细胞分裂。 您的身体必须产生新的骨细胞、 新的皮肤细胞、 新的细胞等等 。
    1. Cell division is also necessary to repair damaged cells. Imagine you cut your finger. After the scab forms, it will eventually disappear and new skin cells will grow to repair the wound. Where do these cells come from? Some of your existing skin cells divide and produce new cells.
      ::细胞分裂也是修复受损细胞所必须的。 想象一下, 你切下手指。 在剖腹产状后, 它最终会消失, 新的皮肤细胞会成长来修复伤口。 这些细胞来自何处? 您现有的部分皮肤细胞会分裂并产生新的细胞 。
    1. Your cells can also simply wear out. Over time you must replace old and worn-out cells. Cell division is essential to this process.
      ::您的单元格也可以简单地耗尽。 随着时间的推移, 您必须替换旧的和破旧的单元格。 单元格分割对于这一过程至关重要 。

    Summary
    ::摘要

    • Cells must divide repeatedly for an embryo to develop or for you to grow.
      ::胚胎发育或生长 细胞必须反复分裂
    • Cells also divide in order to replace damaged or worn-out cells.
      ::电池也分开,以更换受损或破损的电池。

    Explore More
    ::探索更多

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

    • Surface Area to Volume Ratios  at   (2:45)
      ::地表对量比率(2:45)
    1. Does the rate at which materials diffuse into a cell vary with the size of the cell?
      ::材料扩散到细胞的速度是否与细胞大小不同?
    1. What does this mean for large cells?
      ::这对大型细胞意味着什么?

    Review
    ::回顾

    1. Define cell division.
      ::定义单元格分区 。
    1. How does an embryo develop from a fertilized egg?
      ::胚胎如何从受精卵中发育?
    1. List two reasons that cells must divide.
      ::列出单元格必须分割的两种理由。