Section outline

  • What happens if you put a few drops of food coloring in water?
    ::如果你在水里放几滴彩色食物会怎么样?

    Over time, the molecules of color spread out through the rest of the water. When the molecules are evenly spread throughout the space, the water will become an even color. This process of molecules moving from an area where there are lots of molecules to an area where there are fewer molecules is known as diffusion.
    ::随着时间的推移, 色分子会从其余的水中扩散出去。 当分子平均分布于整个空间时, 水会变成一个平衡的颜色。 分子从一个分子数量众多的区域移动到一个分子数量较少的区域, 这个过程被称为“ 扩散 ” 。

    Diffusion
    ::传播

    Small molecules can pass through the plasma membrane through a process called diffusion.  Diffusion  is the movement of molecules from an area where there is a higher  concentration  (larger amount) of the substance to an area where there is a lower concentration (lower amount) of the substance ( Figure   ). The amount of a substance in relation to the total volume is the  concentration . During diffusion, molecules are said to flow down their  concentration gradient , flowing from an area of high concentration to an area of low concentration. Molecules flowing down a concentration gradient is a natural process and does not require  energy .
    ::小分子可以通过一个叫做扩散的过程穿过等离子膜。扩散是指分子从一个物质浓度(大得多)较高的地区转移到一个物质浓度(低量)较低的地区(图 )。相对于总体积而言,一种物质的数量是浓度。在扩散过程中,据说分子会从一个高浓度地区流到一个低浓度地区,并流到一个低浓度地区。向浓度梯度下流的分子是一种自然过程,不需要能量。

    Diffusion can occur across a  semipermeable  membrane, such as the  , as long as a concentration gradient exists. Molecules will continue to flow in this manner until  equilibrium  is reached. At equilibrium, there is no longer an area of high concentration or low concentration, and molecules flow equally in both directions across the semipermeable membrane. At equilibrium, equal amounts of a  molecule  are entering and leaving a  cell .
    ::只要存在浓度梯度,这种半渗透膜即有可能发生扩散。在达到平衡之前,分子将继续以这种方式流动。在平衡时,不再有高浓度或低浓度的区域,分子在半渗透膜两侧均匀流动。在平衡时,分子进入和离开一个细胞的数量相等。

    Diffusion across a cell membrane showing concentration gradient over time.
     
    Diffusion is the movement of a substance from an area of a higher amount toward an area of lower amount. A concentration gradient initially exists across the cell membrane. Equilibrium is reached when there is an equal amount of the substance on both sides of the membrane.

    Osmosis
    ::骨循环

    The diffusion of water across a membrane because of a difference in concentration is called  osmosis . Let's explore three different situations and analyze the flow of water.
    ::由于浓度的差异,水在膜上的扩散被称为渗透。让我们探索三种不同的情况,分析水流。

    1. A  hypotonic  solution  means the environment outside of the cell has a lower concentration of dissolved material than the inside of the cell. If a cell is placed in a hypotonic solution, water will move into the cell. This causes the cell to swell, and it may even burst.
      ::低温溶液是指细胞外的环境溶解材料的浓度低于细胞内,如果将细胞放在低温溶液中,水会流入细胞,导致细胞膨胀,甚至可能爆裂。
    1. A  hypertonic  solution  means the environment outside of the cell has more dissolved material than inside of the cell. If a cell is placed in a hypertonic solution, water will leave the cell. This can cause a cell to shrink and shrivel.
      ::超声波溶液是指细胞外的环境溶解材料多于细胞内,如果将细胞放在超音速溶液中,水就会离开细胞。这可能导致细胞缩缩和缩缩。
    1. An  isotonic solution  is a solution in which the amount of dissolved material is equal both inside and outside of the cell. Water still flows in both directions, but an equal amount enters and leaves the cell.
      ::同位素溶液是一种溶液,溶解材料在细胞内外的数量相等,水仍然流向双向,但进入和离开细胞的数量相等。

    Applications of Osmosis
    ::肠胃病应用

    How do marine  animals  keep their cells from shrinking? How do you keep your   cells from bursting? Both of these questions have to do with the cell membrane and osmosis. Marine animals live in salt water, which is a hypertonic environment; there is more salt in the water than in their cells. To prevent losing too much water from their bodies, these animals intake large quantities of salt water and then secrete the excess salt.  Red blood cells  can be kept from bursting or shriveling if put in a solution that is  isotonic  to the blood cells. If the blood cells were put in pure water, the solution would be hypotonic to the blood cells, so water would enter the blood cells, and they would swell and burst ( Figure   ).
    ::海洋动物如何防止它们的细胞缩小?你怎么防止它们的细胞破裂呢?这两个问题都与细胞膜和宇宙体有关?海洋动物生活在盐水中,这是一个超声层环境;水中盐量比细胞中多。为了防止从它们体内流失过多的水,这些动物摄入大量盐水,然后将多余的盐分分出来。如果将血细胞放入一个对血细胞具有等离子的溶液中,红血细胞可以避免爆发或窒息。如果将血细胞放入纯水中,溶液就是血液细胞的低温,因此水会进入血液细胞,它们会膨胀和破裂(图示 ) 。

    Comparison of red blood cells in hypertonic, isotonic, and hypotonic solutions, showing osmotic effects.
     
    Osmosis causes these red blood cells to change shape by losing or gaining water.

    Summary
     ::摘要

    • Diffusion is the movement of molecules from an area of high concentration to an area of low concentration.
      ::扩散是指分子从高浓度地区向低浓度地区转移。
    • The diffusion of water across a membrane because of a difference in concentration is called osmosis.
      ::由于浓度差异,水通过膜扩散,称为渗透。

    Explore More
    ::探索更多

    Use the resource below to answer the following questions.
    ::使用以下资源回答下列问题。

    • Osmosis  at   (5:07)
      ::5:07时的疾病

     

     

    1. What is osmosis?
      ::什么是渗透?
    1. What is tonicity?
      ::什么是通情达理?
    1. How can a hypotonic solution cause a cell to rupture? Describe this process as specifically as you can.
      ::低度溶液如何导致细胞破裂? 尽可能具体描述这个过程 。
    1. How would a hypertonic solution affect a cell? How could this affect cellular processes?
      ::高音溶液如何影响细胞?这如何影响细胞过程?
    1. Do water molecules leave or enter a cell in an isotonic solution?
      ::水分子是以等离子溶液离开或进入细胞的吗?

    Review
    ::回顾

    1. Describe the process of diffusion.
      ::描述传播过程。
    1. Define osmosis.
      ::定义宇宙。
    1. If a plant cell is placed in a solution and the cell shrivels up, what type of solution was it placed in? How do you know?
      ::如果植物细胞被安置在溶液中,而细胞逐渐萎缩,那么它被安置在哪种溶液中?你怎么知道?