Section outline

  • General

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  • 水与生命

    What you will learn
    ::你会学到什么

    • The distribution of on Earth
      ::地球分布
    • The chemical
      ::化学品
    • How water is important for all life processes
      ::水如何对所有生命过程都很重要

    Iguassu Falls, showcasing powerful waterfalls and lush greenery, emphasizing water's beauty and necessity.

    Dihydrogen oxide, or dihydrogen monoxide. Does this chemical sound dangerous?
    ::氧化二氢或一氧化二氢,这种化学品听起来危险吗?

    Another name for this compound is…water. Water can create some absolutely beautiful sights. Iguassu Falls is the largest series of waterfalls on the planet, located in Brazil, Argentina, and Paraguay. And water is necessary for life. The importance of water to life cannot be emphasized enough. All life needs water. Life started in water. Essentially, without this simple three atom molecule, life would not exist.
    ::这个化合物的另一个名称是...水。水可以创造一些绝对美丽的景象。 Iguassu Falls是地球上最大的一系列瀑布,位于巴西、阿根廷和巴拉圭。水是生命所必需的。水对生命的重要性是无法强调的。所有生命都需要水。生命起源于水中。基本上,没有这三个原子分子,生命就不会存在。

    Water
    ::水 水

    Water, like carbon, has a special role in living things. It is needed by all known forms of life. Water is a simple molecule, containing just three atoms. Nonetheless, water’s structure gives it unique properties that help explain why it is vital to all living organisms .
    ::水像碳一样,在生命中有着特殊的作用。 所有已知生命形式都需要水。 水是一个简单的分子,仅包含三个原子。 尽管如此,水的结构赋予它独特的特性,帮助解释为什么它对所有生物体至关重要。

    Water, Water Everywhere
    ::水、水、无处饮水

    Water is a common chemical substance on planet Earth. In fact, Earth is sometimes called the "water planet" because almost 75% of its surface is covered with water. If you look at the Figure , you will see where Earth’s water is found. The term water generally refers to its liquid state, and water is a liquid over a wide range of temperatures on Earth. However, water also occurs on Earth as a solid (ice) and as a gas (water vapor).
    ::水是地球上常见的化学物质。 事实上,地球有时被称为“水行星 ” , 因为它的表面有近75%的水覆盖着地球。 如果你看一下图,你就会看到地球的水在哪里。 水通常指它的液体状态,水是地球上各种温度的液体。 然而,水也以固体(冰 ) 和气体(水蒸气)的形式出现在地球上。

    Distribution of Earth's water: 97% saltwater, 3% freshwater sources.
    Most of the water on Earth consists of saltwater in the oceans. What percent of Earth’s water is freshwater? Where is most of the freshwater found?

    Structure and Properties of Water
    ::水的结构和属性

    No doubt, you are already aware of some of the properties of water. For example, you probably know that water is tasteless and odorless. You also probably know that water is transparent, which means that light can pass through it. This is important for organisms that live in the water, because some of them need sunlight to make food .
    ::毫无疑问,你已经意识到水的某些特性。例如,你可能知道水的品味和气味是无味的。你可能也知道水是透明的,这意味着光能通过它。这对于生活在水中的生物非常重要,因为有些生物需要阳光做食物。

    Chemical Structure of Water
    ::水的化学结构

    To understand some of water’s properties, you need to know more about its chemical structure. As shown in the Figure , each molecule of water consists of one atom of oxygen (red) and two atoms of hydrogen (white). The oxygen atom in a water molecule attracts negatively-charged electrons more strongly than the hydrogen atoms do. As a result, the oxygen atom has a slightly negative charge, and the hydrogen atoms have a slightly positive charge. A difference in electrical charge between different parts of the same molecule is called polarity , making water a polar molecule .
    ::为了了解水的某些特性, 您需要了解更多关于水化学结构的信息。 如图所示, 每个水分子包括一个氧原子( 红) 和两个氢原子( 白 ) 。 水分子中的氧原子比氢原子更能吸引负载电子。 因此, 氧原子的电荷略为负荷, 氢原子的电荷略有阳性。 同一分子不同部分的电荷差异被称为极性, 使水成为极分子。

    Chemical structure of a water molecule showing one oxygen atom and two hydrogen atoms.

    Opposites attract when it comes to charged molecules. In the case of water, the positive (hydrogen) end of one water molecule is attracted to the negative (oxygen) end of a nearby water molecule. Because of this attraction, weak bonds form between adjacent water molecules. The type of bond that forms between molecules is called a hydrogen bond . Bonds between molecules are not as strong as bonds within molecules. There are just many more hydrogen bonds in water (between water molecules) than there are covalent bonds within a molecule. The hydrogen bonds may not be strong, but in water they are strong enough to hold together nearby molecules.
    ::在水中,一个水分子的正(氢)端被附近水分子的负(氧)端吸引到一个水分子的负(氢)端上。由于这种吸引力,相邻水分子之间形成了微弱的联结。分子之间形成的联结类型被称为氢联结。分子之间的联结不如分子内部的联结那么强大。水中氢联结(水分子之间的联结)比分子内部的共价联结多得多。氢联结可能不强,但在水中,氢联结足够坚固,可以将附近的分子放在一起。

    Because of its polarity, water readily dissolves many substances including ionic compounds like table salt (NaCl). Water molecules stabilize the Na + and Cl - ions that are formed after the ionic bond between them breaks.
    ::由于其极性,水很容易溶解许多物质,包括象桌盐(NaCl)等离子化合物,水分子稳定了纳加和氯离子,这些离子是在它们之间断裂离子后形成的。

     

    Properties of Water
    ::水的属性

    Hydrogen bonds between water molecules explain some of water’s properties. For example, hydrogen bonds explain why water molecules tend to stick together. This property is known as cohesion . Have you ever watched water drip from a leaky faucet or from a melting icicle? If you have, then you know that water always falls in drops rather than as separate molecules.
    ::水分子之间的氢离子可以解释水的某些特性。 比如,氢离子可以解释水分子为何会粘在一起。 这个特性被称为凝固。 你有没有看过从漏水的水龙头或融化冰柱滴水的情况?如果有,那么你就会知道水总是滴在滴子中,而不是作为分离的分子。

    Another important physical property of water is adhesion . In terms of water, adhesion is the bonding of a water molecule to another substance, such as the sides of a leaf's veins . This process happens because hydrogen bonds are special in that they break and reform with great frequency. This constant rearranging of hydrogen bonds allows a percentage of all the molecules in a given sample to bond to another substance. This grip-like characteristic that water molecules form causes capillary action, the ability of a liquid to flow against gravity in a narrow space. An example of capillary action is when you place a straw into a glass of water. The water seems to climb up the straw before you even place your mouth on the straw.
    ::水的另一个重要物理特性是粘合。在水方面,粘合是水分子与另一种物质(如叶叶的侧面)的结合。这一过程之所以发生,是因为氢联结具有特殊性,因为氢联结断裂和非常频繁地改造。氢联结的这种持续重新排列使特定样本中所有分子的一定比例能够与另一种物质相连接。水分子形成这种紧凑的特征导致毛细作用,液体在狭小空间中对重力流动的能力。一个毛细作用的例子就是将一根稻草放入水杯中。水似乎爬上你面前的稻草,甚至把嘴放在稻草上。

    Adhesion, cohesion and capillary action are necessary to the survival of most organisms. It is the mechanism that is responsible for water transport in plants through and (see Figure ), and in through small .
    ::多数生物的生存离不开粘合、凝聚和毛细行动,而是负责通过植物和通过小植物(见图 )和通过小植物(见图 ) 进行水运的机制。

    Water Transport In A Plant, Depicting Cohesion And Adhesion Effects.
    Evaporation of water through transpiration causes the movement of water in plants.
    Water moves up the stem by cohesion and adhesion.

     

    Hydrogen bonds cause water to have a relatively high boiling point of 100°C (212°F). Because of its high boiling point, most water on Earth is in a liquid state rather than in a gaseous state. Water in its liquid state is needed by all living things. Hydrogen bonds also cause water to expand when it freezes. This, in turn, causes ice to have a lower density (mass/volume) than liquid water. The lower density of ice means that it floats on water. For example, in cold climates, ice floats on top of the water in lakes. This allows lake animals such as to survive the winter by staying in the water under the ice.
    ::氢结层导致水具有100°C(212°F)这一相对较高的沸点。由于其高温点,地球上的水大多处于液态,而不是气体状态。所有生物都需要液态的水。氢结层在冷冻时也会导致水膨胀。这反过来又导致冰的密度(质量/体积)低于液态水。冰的密度较低意味着它在水上漂浮。例如,在寒冷的气候下,湖泊水面顶部的冰浮。这允许湖内动物在冰层下生存,如在水中生存等。

    Water and Life
    ::水与生命

    The is about 70% water (not counting the water in body fat, which varies from person to person). The body needs all this water to function normally. Just why is so much water required by human beings and other organisms? Water can dissolve many substances that organisms need, and it is necessary for many . The examples below are among the most important biochemical processes that occur in living things, but they are just two of many ways that water is involved in biochemical reactions.
    ::水大约占水量的70%(不包括人与人之间不同的体脂肪水)。身体需要所有水才能正常运转。为什么人类和其他生物体需要这么多水?水能溶解许多生物体需要的物质,对许多生物体来说是必要的。下面的例子就是生命中最重要的生化过程,但是水在生化反应中只是两种方式中的两种。

    • Photosynthesis—In this process, use the energy in sunlight to change carbon dioxide and water to glucose and oxygen. Water is a reactant in this process. The reactions of can be represented by the chemical equation
      ::光合作用-在此过程中,利用阳光中的能量将二氧化碳和水变成葡萄糖和氧气,水是这一过程的一种反应剂。

                               6CO 2 + 6H 2 O + Energy → C 6 H 12 O 6 + 6O 2
    ::6CO2 + 6H2O + 能源 C6H12O6 + 6O2

    • Cellular respiration—In this process, cells break down glucose in the presence of oxygen and release carbon dioxide, water (a product), and energy. The reactions of can be represented by the chemical equation
      ::细胞呼吸——在这一过程中,细胞在氧气和释放二氧化碳、水(一种产品)和能量的情况下分解葡萄糖。

                               C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + Energy
    ::C6H12O6 + 6O2 + 6O2 + 6CO2 + 6H2O+ 能源

    Water is involved in many other biochemical reactions. As a result, just about all life processes depend on water. Clearly, life as we know it could not exist without water.
    ::水涉及许多其他生物化学反应。 因此,几乎所有生命过程都依赖于水。 显然,我们知道生命没有水是不可能存在的。

     

     

     

     

    Summary
    ::摘要

    • Water is needed by all known forms of life.
      ::所有已知生命形式都需要水。
    • Due to the difference in the distribution of charge, water is a polar molecule.
      ::由于电荷分布的不同,水是一种极分子。
    • Hydrogen bonds hold adjacent water molecules together.
      ::氢联结将相邻的水分子聚集在一起。
    • Water has several important properties including cohesion, adhesion and a relatively high boiling point.
      ::水具有若干重要特性,包括凝聚、粘合和相对较高的沸点。
    • Water is involved in many biochemical reactions. As a result, just about all life processes depend on water.
      ::水涉及许多生化反应,因此,几乎所有生命过程都依赖于水。

    Review
    ::回顾

    1. Where is most of Earth’s water found?
      ::地球的大部分水在哪里?
    2. What percent of Earth’s water is freshwater?
      ::淡水占地球水量的百分比是多少?
    3. What is polarity? Describe the polarity of water.
      ::什么是极性?描述水的极性。
    4. How could you demonstrate to a child that solid water is less dense than liquid water?
      ::你怎么能向孩子证明 固体水比液态水密度低?
    5. Explain how water’s polarity is related to its boiling point.
      ::解释水的极性与沸点有何关联。
    6. Explain why metabolism in organisms depends on water.
      ::解释为什么生物的新陈代谢依赖水。