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  • 水与生命

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    The Blue Marble
    ::蓝色大理石

    It's often called the " planet," and it's been given the nickname "the blue marble." You probably just call it "home." Almost three-quarters of our home planet is covered by water, and without it, life as we know it could not exist on Earth. Water, like carbon, has a special role in living things. It is needed by all known forms of life. Although water consists of simple molecules, each containing just three atoms, its structure gives it unique properties that help explain why it is vital to all living organisms .
    ::它经常被称为“地球”, 它被命名为“蓝色大理石 ” 。 你可能只是把它称为“家 ” 。 我们家星球上几乎四分之三的地球被水覆盖着, 没有水,我们知道地球上不可能存在的生命, 水,像碳一样,在生命中有着特殊的作用。所有已知的生命形式都需要它。虽然水由简单的分子组成,每个分子只包含三个原子,但水的结构给它提供了独特的特性,帮助解释为什么它对所有生物体都至关重要。

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

    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. Water, however, also occurs on Earth as a solid (ice) and as a gas (water vapor).
    ::如果你看一下这个数字,你就会看到地球的水在哪里被发现。 水通常指其液体状态,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。

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    Most of the water on Earth consists of saltwater in the oceans. What percent of Earth’s water is fresh water? Where is most of the fresh water found?
    ::地球上的水大部分是海水中的盐水。 地球上的水中有多少是淡水? 大部分淡水在哪里?

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

    You are probably already aware of some of the properties of water. For example, you 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 by .
    ::你可能已经意识到水的某些特性。例如,你知道水没有品味和气味。你可能也知道水是透明的,这意味着光能穿过它。这对生活在水中的生物非常重要,因为有些生物需要阳光才能生产食物。

    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. Each molecule of water consists of one atom of oxygen and two atoms of hydrogen. The oxygen atom in a water molecule attracts 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 . The diagram shows water’s polarity.
    ::为了了解水的某些特性,您需要更多地了解水的化学结构。每个水分子由一个原子的氧和两个原子的氢组成。水分子中的氧原子比氢原子更能吸引电子。因此,氧原子的电荷略有负值,氢原子的电荷略有正值。同一分子不同部分的电荷差异被称为极性。图表显示了水的极度。

    Water Molecule. This diagram shows the positive and negative parts of a water molecule. It also depicts how a charge, such as on an ion (Na or Cl, for example) can interact with a water molecule.
    ::水分子。 此图显示了水分子的正和负部分。 该图还描述了电荷如何与水分子相互作用, 例如电离( Na 或 Cl ) 。

    W hen it comes to charged molecules, opposites attract. 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, as shown in the diagram . The type of bond that forms between molecules is called a hydrogen bond . Bonds between molecules are not as strong as bonds within molecules, but in water, they are strong enough to hold together nearby molecules.
    ::当涉及到充电分子时,反向吸引。在水方面,一个水分子的正(氢)端被附近水分子的负(氧)端吸引。由于这种吸引力,相邻水分子之间形成了微弱的联结,如图所示。分子之间形成的联结类型被称为氢联结。分子之间的联结不及分子内部的联结,而是在水中,它们足够强大,足以将附近的分子凝结在一起。

    Hydrogen Bonding in Water Molecules. Hydrogen bonds form between nearby water molecules. How do you think this might affect water’s properties?
    ::氢联结在水分子中。 附近水分子之间形成了氢联结。 你认为这会如何影响水的特性?

    Properties of Water
    ::水的属性

    Hydrogen bonds between water molecules explain some of water’s properties — for example, why water molecules tend to "stick" together. Did you ever watch water drip from a leaky faucet or from a melting icicle? If you did, then you know that water always falls in drops, rather than as separate molecules. The dew drops pictured are another example of water molecules sticking together.
    ::水分子之间的氢离子可以解释水的某些特性,例如,为什么水分子倾向于“粘合 ” 。 你有没有看过从漏水的水龙头或融化冰柱滴水?如果你看过,那么你就会知道水总是滴落在滴滴中,而不是作为分离的分子。 露水滴是水分子凝聚的另一个例子。

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    Dew drops cling to the petals of a yellow rose in this picture. Can you think of other examples of water forming drops? Hint: What happens when it rains on a newly waxed car?
    ::照片中黄玫瑰的花瓣紧紧粘着双滴滴。 你能想象水形成滴滴的其他例子吗? 提示:当新蜡车下雨时会怎样?

    Hydrogen bonds cause water to have a relatively high boiling point of 100°C (212°F). Extra energy is needed to break these bonds and separate water molecules so they can escape into the air as water vapor. Because of its high boiling point, most water on Earth is in a liquid state, rather than 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 (that is, less mass per unit volume) than liquid water. The lower density of ice means that it floats on water. In cold climates, ice floats on top of the water in lakes. This allows lake like   to survive the winter by staying in the liquid water under the ice.
    ::氢离子导致水的沸点相对较高,为100°C(212°F)。需要额外的能量来打破这些结点和分离水分子,以便它们能作为水蒸气逃入空气中。由于沸点高,地球上的水大多处于液态,而不是气态状态。所有生物都需要液体状态的水。氢离子在冷冻时还会导致水膨胀。这反过来又导致冰的密度(即每单位体积的质量较低)低于液体水。冰的密度较低意味着它会浮在水中。在寒冷的气候下,湖泊的水顶部会浮冰。这让湖在冰下的液体水中生存到冬天。

    Water and Living Things
    ::水与生活

    The is about 70 percent 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. Water's polarity helps it dissolve other polar substances. Water is also necessary for many . The examples below are among the most important biochemical processes that occur in living things, but they are just two of the many ways that water is involved in biochemical reactions.
    ::水大约占水量的70%(不包括人体脂肪中的水,这种水因人而异)。身体需要所有这些水才能正常运转。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。水的极性有助于它溶解其他极性物质。水对许多人来说也是必要的。下面的例子是生命中最重要的生化过程,但水只是生物化学反应中水参与的多种方法中的两种。

    • Photosynthesis: In this process, use the energy in sunlight to change carbon dioxide and water to glucose and oxygen. The reactions of photosynthesis 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转化为葡萄糖和氧气。光合作用的反应可以用化学方程式表示:

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

    • :  In this process, cells break down glucose in the presence of oxygen and release carbon dioxide, water, and energy. The reactions of cellular respiration can be represented by the chemical equation:
      :::在这一过程中,细胞在氧气条件下分解葡萄糖,释放二氧化碳、水和能量。细胞呼吸的反应可以用化学方程式表示:

                      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. Almost all life processes depend on water.
    ::水涉及许多其他生物化学反应,几乎所有生命过程都依赖于水。

    Feature: My Human Body
    ::特质:我的人体

    Are you a marathon runner or other endurance athlete? Do you live and work in a hot, humid climate ? If you answered "yes" to either question, you may be at risk of water intoxication.
    ::你们是马拉松赛跑者或其他耐力运动员吗?你们是在炎热潮湿的气候中生活和工作吗?如果你们回答“同意”任一问题,你们可能面临水中毒的风险。

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    Marathon runners are especially at risk of developing water intoxication.
    ::马拉松赛跑者特别容易产生水中毒。

    Water is considered the least toxic chemical compound, so it may surprise you to learn that drinking too much water can cause serious illness and even death. Water intoxication is a potentially fatal disturbance in brain functions. It results when the normal balance of sodium and other electrolytes in the body is pushed outside safe limits by overhydration, or taking in too much water. The condition is also called hyponatremia , which refers to a lower-than-normal level of sodium in the that occurs when more water is entering than leaving the body.
    ::水被认为是毒性最小的化学化合物,所以你可能会惊讶地知道,喝太多的水会导致严重疾病甚至死亡。水中毒是大脑功能中潜在的致命干扰。当体内钠和其他电解质的正常平衡因水分过量或摄入过多而排出安全限度之外时,就会发生这种情况。 这种状况也被称为低纳特雷米,这是指进入水量大于离开水量时出现的低于正常水平的钠。

    As excessive water is consumed, fluid outside the cells decreases in its concentration of sodium and other electrolytes relative to the concentration inside the cells. This causes fluid to enter the cells by to balance the electrolyte concentration. The extra fluid in the cells causes them to swell. In the brain, this swelling increases the pressure inside the skull. It is this increase in pressure that leads to the first observable symptoms of water intoxication, which typically include headache, confusion, irritability, and drowsiness. As the condition worsens, additional symptoms may occur, such as difficulty during exertion, muscle weakness and pain, or nausea and vomiting. If the condition persists, the cells in the brain may swell to the point where blood flow is interrupted or pressure is applied to the brain stem . This is extremely dangerous and may lead to seizures, brain damage, coma, or even death.
    ::随着过量水的消耗,细胞外的液体会比细胞内的浓度减少钠浓度和其他电解液,从而通过电解浓度平衡液体进入细胞。细胞中的额外液体会使细胞膨胀。在大脑中,这种膨胀会增加头骨内的压力。正是这种压力的增加导致第一批可观测到的水中毒症状,通常包括头痛、混乱、不适和沉睡。随着病情恶化,还可能出现更多的症状,例如施用困难、肌肉疲软和疼痛、恶心和呕吐。如果情况持续下去,大脑中的细胞可能会膨胀到血液流动中断或对脑干施压的地步。这极危险,甚至可能导致癫痫、脑损伤、昏迷甚至死亡。

    Under normal circumstances, it is very rare to accidentally consume too much water. However, it is relatively common in athletes who participate in endurance activities, such as marathon running. A study conducted on participants of the 2002 Boston Marathon, for example, found that 13  percent of the runners finished the race with water intoxication. The study also found that water intoxication was just as likely to occur in runners who drank sports drinks containing electrolytes as those who drank plain water. Water intoxication is so common at marathon events that medical personnel who work at such events are trained to suspect water intoxication when runners collapse or show signs of confusion.
    ::在正常情况下,意外消耗过多水的情况非常罕见,但是,在参加诸如马拉松跑步等耐力活动的运动员中,这种情况比较常见。例如,对2002年波士顿马拉松赛的参加者进行的一项研究发现,13%的跑者在比赛中喝完水中中毒;研究还发现,饮用含有电解剂的体育饮料的跑者与饮用纯水的跑者同样可能发生水中毒。马拉松赛事中,水中毒现象十分普遍,因此,在马拉松赛事中工作的医务人员在跑者倒下或出现混乱迹象时,都受过关于怀疑水中毒的培训。

    Because of the publicity water intoxication has received lately, sports experts have lowered  their recommendations for water intake during endurance events. They now advise drinking only when thirsty rather than drinking to "stay ahead of thirst," which they recommended previously . Keeping water intake in line with water loss is the best way to prevent water intoxication. Mild water intoxication can be treated by restricting fluid intake. In more severe cases, treatment may require the use of diuretic drugs (which increase urination) or other types of drugs to reduce blood volume. Serious water intoxication should be considered a true medical emergency.
    ::最近,由于宣传水的中毒现象,体育专家降低了对耐久性事件期间水摄取的建议,现在他们建议只有在渴时才饮用,而不是饮用,以达到他们以前的建议的 " 口渴前期 " 。 保持水摄取与缺水相一致是防止水中毒的最佳办法。 轻水中毒可以通过限制液体摄取来治疗。 在更严重的情况下,治疗可能需要使用尿素药物(增加尿液)或其他类型的药物来减少血量。 严重的水中毒应被视为真正的医疗紧急情况。

    Summary
    ::摘要

    • Most water on Earth consists of salt water in the oceans. Only a tiny percentage of the Earth's water is fresh liquid water.
      ::地球上的大部分水由海洋中的盐水组成,地球水中只有一小部分是淡水。
    • Virtually all living things on Earth require liquid water. Water exists as a liquid over a wide range of temperatures and dissolves many substances. These properties depend on water's polarity, which causes water molecules to "stick" together.
      ::地球上几乎所有生物都需要液态水。 水作为一种液体存在于广泛的温度上,溶解了许多物质。 这些特性取决于水的极性,它使水分子“粘合在一起 ” 。
    • The human body is about 70 percent water (outside of fat). Organisms need water to dissolve many substances and for most biochemical processes, including photosynthesis and cellular respiration.
      ::人体大约是70%的水(脂肪外)。 生物需要水来溶解许多物质和大部分生化过程,包括光合作用和细胞呼吸。

    Review
    ::回顾

    1. Where is most of Earth's fresh water found?
    ::1. 地球大部分淡水在哪里?

    2. Identify properties of water.
    ::2. 查明水的特性。

    3. What is polarity? Explain why water molecules are polar.
    ::3.什么是极性?解释为什么水分子是极性。

    4. Why do water molecules tend to "stick" together?
    ::4. 为什么水分子倾向于“棍子”在一起?

    5. What role does water play in photosynthesis and cellular respiration?
    ::5. 水在光合作用和细胞呼吸方面起什么作用?

    6. Which do you think is stronger: the bonds between the hydrogen and oxygen atoms within a water molecule, or the bonds between the hydrogen and oxygen atoms between water molecules? Explain your answer.
    ::6. 你认为哪个更强:水分子中的氢原子和氧原子之间的关联,或者水分子中的氢原子和氧原子之间的关联?解释你的答复。

    7. Given what you’ve learned about water intoxication (or hyponatremia), explain why you think drinking salt water would be bad for your cells.
    ::7. 鉴于你对水中毒(或低纳特雷米亚)的认识,

    8. What is the name for the bonds that form between water molecules?
    ::8. 水分子之间形成的联系的名称是什么?

    9. Explain why water can dissolve other polar molecules.
    ::9. 解释为什么水能溶解其他极分子。

    10. If there is pollution in the ocean that causes the water to become more cloudy or opaque, how do you think the ocean's  photosynthetic organisms will be affected? Explain your answer.
    ::10. 如果海洋中存在污染,导致水更加多云或不透明,那么你认为海洋的光合生物将受到何种影响?解释你的答复。

    11. The boiling point of water is 100°C (212°F) and the freezing point is 0°C (32°F).
    ::11. 水的沸点为100°C(212°F),冷点为0°C(32°F)。

    a. What is the state of water at 75°C?
    ::a. 75°C的水状况如何?

    b. What is the state of water at 28°F?
    ::b. 28°F的水状况如何?

    c. What is the state of water at 105°C?
    ::c. 105°C的水状况如何?

     

    12. Describe one way in which your body gets rid of excess water.
    ::12. 描述你的身体如何摆脱多余的水的一种方式。

     

    13. True or False:  Ice floats on top of water because it is denser than water.
    ::13. 真实或假:冰浮在水上,因为它比水密度高。

    Explore More
    ::探索更多

    Fresh water can be very scarce  in certain areas. Watch the video below to learn about traditional water harvesting techniques in India's Golden Desert. 
    ::某些地方的淡水非常稀少。 看下面的录像, 了解印度金沙漠的传统集水技术。


    The video below discusses water's molecular structure, including  hydrogen bonds.
    ::下面的录像讨论水的分子结构,包括氢联结。