章节大纲

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    Letting in the Light
    ::将光放入光明

    Look at the big windows and glass doors in this house. Imagine all the light they must let in on a sunny day. Now imagine living in a house that has walls without any windows or doors. Nothing could enter or leave. Or imagine living in a house with holes in the walls instead of windows and doors. Things could enter or leave, but you couldn’t control what came in or went out. Only when a house has walls with windows and doors that can be opened or closed can you control what enters or leaves. Windows and doors allow you to let in light and the family dog and keep out rain and bugs, for example. 
    ::看看这栋房子的大窗和玻璃门。 想象一下他们必须在阳光明媚的一天让出所有的灯光。 现在想象一下他们必须让出所有的灯光。 想象一下他们生活在一栋没有窗户或门的房屋里。 没有任何东西可以进入或离开。 或者想象一下住在一栋墙上有洞而不是窗户和门的房屋里。 事情可以进入或离开,但是你无法控制进或出的东西。 只有房子有窗户和门,可以打开或关闭,才能控制进出的东西。 窗窗和门允许你让灯光和家狗进来,并保持雨和虫,比如雨和虫。

    Transport Across Membranes
    ::横跨膜膜运输

    If a were a house, the plasma membrane would be walls with windows and doors. Moving things in and out of the cell is an important function  of the plasma membrane. It controls everything that enters and leaves the cell. There are two basic ways that substances can cross the plasma membrane: passive transport — which requires no energy expenditure by  the cell — and — which requires energy from the cell.
    ::如果是一个房子,等离子膜就是有窗户和门的墙壁。把东西搬进和搬出细胞是等离子膜的一个重要功能。它控制着进出细胞的所有物质。物质可以穿过等离子膜有两种基本方法:被动运输——细胞不需要能源支出——以及需要细胞能量的被动运输。

    Transport Without Energy Expenditure B y The Cell
    ::按小组分列的无能源运输(无能源)

    Passive transport occurs when substances cross the plasma membrane without any input of energy from the cell. No energy is required  because the substances are moving from an area where they have a higher concentration to an area where they have a lower concentration. Concentration refers to the number of particles of a substance per unit of volume. The more particles of a substance in a given volume, the higher the concentration. A substance always moves from an area where it is more concentrated to an area where it is less concentrated.
    ::当物质通过等离子膜而没有从细胞中输入任何能量时,即发生被动迁移。不需要能量是因为物质正在从它们具有较高浓度的地区转移到它们具有较低浓度的地区。浓度是指物质每单位体积的颗粒数量。物质在某一体积中的粒子数量越多,浓度就越高。物质总是从它较集中的地区转移到它较不集中的地区。

    There are several different types of passive transport, including simple , , and facilitated diffusion . Each type is described below.
    ::存在着几种不同类型的被动运输,包括简单的、便利的传播。

    Simple Diffusion
    ::简单传播

    Diffusion is the movement of a substance due to a difference in concentration. It happens without any help from other molecules. The substance simply moves from the area  where it is more concentrated to the area  where it is less concentrated. The figure shows how diffusion works across a . Substances that can squeeze between the molecules in the plasma membrane by simple diffusion are generally very small, hydrophobic molecules, such as molecules of oxygen and carbon dioxide.
    ::扩散是指物质由于浓度差异而转移。它发生时没有任何其他分子的帮助。该物质简单地从它比较集中的地区移到它比较集中的地区。图示显示了它如何扩散到一个地区。可以通过简单的扩散在等离子膜分子之间挤压的物质一般是很小的疏水分子,例如氧和二氧化碳分子。

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    Diffusion Across a Cell Membrane. Molecules diffuse across a membrane from an area of higher concentration to an area of lower concentration until the concentration is the same on both sides of the membrane.
    ::分子在膜膜上扩散,从高浓度地区扩散到低浓度地区,直到薄膜两侧的浓度相同。

    Osmosis
    ::骨循环

    Osmosis is a special type of diffusion — the diffusion of molecules across a membrane. Like other molecules, water moves from an area of higher concentration to an area of lower concentration. Water moves in or out of a cell until its concentration is the same on both sides of the plasma membrane.
    ::骨质疏松是一种特殊的传播类型,即分子在膜上扩散,与其他分子一样,水从高浓度地区移动到低浓度地区,水进出细胞,直至血浆膜两侧的浓度相同。

    Facilitated Diffusion
    ::推动传播

    Water and many other substances cannot simply diffuse across a membrane. Hydrophilic molecules, charged ions , and relatively large molecules (such as glucose) all need help with diffusion. This  help comes from special in the membrane known as transport proteins . Diffusion with the help of transport proteins is called facilitated diffusion . There are several types of transport proteins, including channel proteins and carrier proteins . Both are shown in the figure .
    ::水和其他许多物质不能简单地在膜上扩散。 水文分子、充电离子和相对较大分子(如葡萄糖)都需要在扩散方面得到帮助。这种帮助来自被称为运输蛋白的膜的特殊用途。在运输蛋白的帮助下传播被称为便利的传播。有几种类型的运输蛋白,包括渠道蛋白和载体蛋白。两者都见于图中。

    • Channel proteins form pores (or tiny holes) in the membrane. This allows water molecules and small ions to pass through the membrane without coming into contact with the hydrophobic tails of the lipid molecules in the interior of the membrane.
      ::通道蛋白质在膜内形成孔孔(或小孔),允许水分子和小离子通过膜,而不接触膜内脂肪分子的疏水尾巴。
    • Carrier proteins bind with specific ions or molecules. In doing so, they change shape. As carrier proteins change shape, they carry the ions or molecules across the membrane.
      ::载体蛋白与特定的离子或分子结合, 从而改变形状。 随着载体蛋白改变形状, 它们携带离子或分子横跨膜。

    LadyofHats, modified by Hana Zavadska

    Facilitated Diffusion Across a Cell Membrane. Channel proteins and carrier proteins help substances diffuse across a cell membrane. In this diagram, the channel and carrier proteins are helping substances move into the cell (from the extracellular space to the intracellular space).
    ::通道蛋白质和载体蛋白有助于物质通过细胞膜扩散,在本图中,通道和载体蛋白帮助物质进入细胞(从外细胞空间到细胞内部空间)。

    Transport and Homeostasis
    ::运输与保持原生状态

    For a cell to function normally, the inside of it must maintain a stable state . The concentrations of salts, nutrients , and other substances must be kept within certain ranges. The state in which stable conditions are maintained inside a cell (or an entire organism) is called . Homeostasis requires constant adjustments, because conditions are always changing both inside and outside the cell. The transport of substances into and out of cells as described in this section  plays an important role in homeostasis. By allowing the movement of substances into and out of cells, transport keeps conditions within normal ranges inside the cells and throughout the organism as a whole.
    ::为使细胞正常运转,其内部必须保持稳定的状态;盐类、营养素和其他物质的浓度必须保持在一定的范围之内; 细胞(或整个生物体)内保持稳定条件的状态称为:. 恒定状态需要不断调整,因为细胞内外的条件总是在变化; 本节所述物质进出细胞的运输在常态状态中起着重要作用; 通过允许物质进出细胞,运输使细胞内和整个生物体内的条件保持在正常范围之内。

    Summary
    ::摘要

    • Controlling the movement of  things in and out of the cell is an important function  of the plasma membrane. There are two basic ways that substances can cross the plasma membrane: passive transport — which requires no energy expenditure by the cell — and active transport — which requires energy.
      ::控制物质进出细胞的移动是等离子膜的一个重要功能,物质能够跨越等离子膜有两种基本途径:被动运输——细胞不需要能源支出——和主动运输——需要能源。
    • No energy is needed from the cell for passive transport because it occurs when substances move naturally from an area of higher concentration to an area of lower concentration.
      ::被动运输不需要细胞的能量,因为当物质从高浓度地区自然迁移到低浓度地区时,就会产生这种能量。
    • Simple diffusion is the movement of a substance due to differences in concentration. It happens without any help from other molecules. This is how very small, hydrophobic molecules (such as oxygen and carbon dioxide) enter and leave the cell.
      ::简单的扩散是物质由于浓度差异而移动。它发生时没有任何其他分子的帮助。这就是非常小的疏水分子(如氧和二氧化碳)进入和离开细胞的方式。
    • Osmosis is the diffusion of water molecules across a membrane. Water moves in or out of a cell by osmosis until its concentration is the same on both sides of the plasma membrane.
      ::Osmosis是水分子通过膜扩散,水通过宇宙进入或流出细胞,直至血浆膜两侧的浓度相同。
    • Facilitated diffusion is the movement of a substance across a membrane due to differences in concentration, but it only occurs with the help of transport proteins (such as channel proteins or carrier proteins) in the membrane. This is how large or hydrophilic molecules and charged ions enter and leave the cell.
      ::便利扩散是指一种物质由于浓度差异而跨膜移动,但只有在膜内运输蛋白(如通道蛋白或载体蛋白)的帮助下才能扩散,这就是大型或流体性分子和充电离子进入和离开细胞的方式。
    • Processes of passive transport play important roles in homeostasis. By allowing the movement of  substances into and out of the cell, they keep conditions within normal ranges inside the cell and the organism as a whole.
      ::被动运输过程在自闭状态中起着重要作用,允许物质进出细胞,使细胞和整个生物体内的条件保持在正常范围内。

    Review
    ::回顾

    1. What is the main difference between passive and active transport?
    ::1. 被动和主动运输之间的主要区别是什么?

    2. Summarize three different ways that passive transport can occur. Give an example of a substance that is transported in each way.
    ::2. 概述被动运输可能发生的三种不同方式:举例说明每种方式运输的物质。

    3. Explain how transport across the plasma membrane is related to homeostasis of the cell.
    ::3. 解释等离子膜的运输与电池的均匀状态如何相关。

    4. In general, why can  only very small, hydrophobic molecules cross the cell membrane by simple diffusion?
    ::4. 一般而言,为什么只有很小的疏水分子可以通过简单的扩散穿过细胞膜?

    5. Explain how facilitated diffusion assists with osmosis in cells. D efine osmosis and facilitated diffusion in your answer.
    ::5. 解释促进扩散如何有助于细胞中的渗透,界定渗透,并促进回答中的传播。

    6. Imagine a hypothetical cell with a higher concentration of glucose inside the cell than outside. Answer the following questions about this cell, assuming all transport across the membrane is passive, not active.
    ::6. 想象一个假设的细胞,细胞内葡萄糖浓度高于外表,回答以下关于细胞的问题,假设穿越膜的所有运输都是被动的,而不是主动的。

    a. Can the glucose simply diffuse across the cell membrane? Why or why not?
    ::a. 葡萄糖能否简单地扩散到细胞膜之间?为什么或为什么不能?

    b. Assuming that there are glucose transport proteins in the cell membrane, which way would glucose flow — into or out of the cell? Explain your answer.
    ::b. 假设细胞膜内含有葡萄糖运输蛋白,而葡萄糖流入或流出细胞的方式如何?解释你的答复。

    c. If the concentration of glucose was equal inside and outside of the cell, do you think there would be a net flow of glucose across the cell membrane in one direction or the other? Explain your answer.
    ::c. 如果葡萄糖在细胞内外的浓度相等,你是否认为细胞膜的某一方向或另一方向会有葡萄糖净流动?解释你的答复。

     

    7. What are the similarities and differences between channel proteins and carrier proteins?
    ::7. 渠道蛋白质和载体蛋白之间有什么相似和不同?

     

    8. True or False:  Only active transport, not passive transport, involves transport proteins.
    ::8. 真实或假:只有主动运输,而不是被动运输,涉及运输蛋白质。

     

    9. True or False:  Oxygen and carbon dioxide can squeeze between the lipid molecules in the plasma membrane.
    ::9. 真实或假:氧和二氧化碳可以在等离子膜中的脂分子之间挤压。

     

    10. True or False:  Ions easily diffuse across the cell membrane by simple diffusion.
    ::10. 真实或假:通过简单的扩散很容易在细胞膜之间扩散。

     

    11. Controlling what enters and leaves the cell is an important function of the:
    ::11. 控制细胞的进出是下列单位的一个重要功能:

    a. nucleus
    ::a. 核心核心

    b. vesicle
    ::b. 冰球

    c. plasma membrane
    ::c. 等离子膜

    d. Golgi apparatus
    ::d. Golgi装置

    Explore More
    ::探索更多

    This video shows a short  animation of passive transport.   
    ::这段影片展示了被动运输的简短动画。

     

    Check out this video to learn more about osmosis and tonicity:
    ::校对:Portnoy