章节大纲

  • 常规

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  • 光合作用

    What will you learn
    ::你会学到什么

    • The process of photosynthesis
      ::光合作用进程
    • How capture sunlight
      ::如何捕捉阳光
    • How light energy is converted into chemical energy
      ::如何将光能转换成化学能源

    Photosynthesis showing sunlight, water, carbon dioxide, and byproduct oxygen.

    Oxygen has been described as a ‘‘waste product.’’ Is it?
    ::氧气被描述为废物产品。"是么?

    Essentially, oxygen is a waste product of the of photosynthesis. It is a ‘‘leftover’’ from a necessary part of the process. All the oxygen that is necessary to maintain most forms of life just happens to come about during this process.
    ::基本上,氧是光合作用产生的废物。它是过程一个必要部分的剩余部分。维持大多数生命形式所需的所有氧气在此过程中碰巧出现。

    Photosynthesis Stage I: The Light Reactions
    ::光合成阶段一:光反应

    Chloroplasts Capture Sunlight
    ::日光

    Every second, the sun fuses over 600 million tons of hydrogen into approximately 596 million tons of helium, converting over 4 million tons of matter (4.3 billion kg) into light and heat energy. Countless tiny packets of that light energy travel 93 million miles (150 million km) through space, and about 1% of the light which reaches the Earth’s surface participates in photosynthesis. Light is the source of energy for photosynthesis, and the first set of reactions which begin the process requires light – thus the name, light reactions , or light-dependent reactions.
    ::每秒,太阳将6亿吨以上的氢解成约5.96亿吨的氦,将400万吨物质(43亿公斤)转化为光能和热能。 光能的无数小包小包通过空间漂移9300万英里(1.5亿公里 ) , 到达地球表面的大约1%的光线都参与光合作用。 光是光合作用能源的来源,而开始这一过程的第一套反应需要光光 — — 也就是名称、光反应或光依赖反应。

    When light strikes chlorophyll (or an accessory pigment) within the chloroplast, it energizes electrons within that molecule. These electrons jump up to higher energy levels; they have absorbed or captured, and now carry, that energy. High-energy electrons are “excited.” Who wouldn’t be excited to hold the energy for life?
    ::当光在叶绿板内撞击叶绿素(或附属色素 ) , 光能在该分子内激活电子。 这些电子跳到更高的能量水平;它们吸收或捕捉了,现在携带了这种能量。 高能电子“兴奋 ” 。 谁会不兴奋地抓住生命的能量呢?

    The excited electrons leave chlorophyll to participate in further reactions, leaving the chlorophyll “at a loss”; eventually they must be replaced. That replacement process also requires light, working with an complex to split molecules. In this process of photolysis (“splitting by light”), H 2 O molecules are broken into hydrogen ions , electrons, and oxygen atoms. The electrons replace those originally lost from chlorophyll. Hydrogen ions and the high-energy electrons from chlorophyll will carry on the energy transformation after the light reactions are over.
    ::兴奋电子让叶绿素进一步参与反应,使叶绿素“丢失”;最终必须替换它们。替换过程还需要光线,与一个复合体合作分裂分子。在这一光解过程(“光分解 ” ) 中,H2O分子被破碎成氢离子、电子和氧原子。电子将取代最初从叶绿素中损失的。叶绿素中的氢离子和高能电子将在光反应结束后继续进行能量转换。

    DID YOU KNOW?
    Elysia chlorotica , a of green sea slug, takes chloroplasts from and places them into its own digestive . This enables these to capture solar energy and perform photosynthesis.
     

    The oxygen atoms, however, form oxygen gas, which is a waste product of photosynthesis. The oxygen given off supplies most of the oxygen in our atmosphere . Before photosynthesis evolved, Earth’s atmosphere lacked oxygen altogether, and this highly reactive gas was toxic to the many organisms living at the time. Something had to change! Most contemporary organisms rely on oxygen for efficient respiration . So plants don’t just “restore” the air, they also had a major role in creating it!
    ::然而,氧原子形成氧气,这是光合作用产生的废气。 氧气从大气中释放出来,提供了大部分氧气。 在光合作用演变之前,地球的大气完全缺乏氧气,而这种高度反应性气体对当时生活的许多生物有毒。必须改变一些东西。大多数当代生物依靠氧进行高效的呼吸。因此植物不仅“恢复”空气,而且在创造空气方面也起着重要作用。

    To summarize, chloroplasts “capture” sunlight energy in two ways. Light ‘‘excites’’ electrons in pigment molecules, and light provides the energy to split water molecules, providing more electrons as well as hydrogen ions.
    ::简言之,叶绿石以两种方式“捕捉”阳光能量。 色素分子中的光电和光能为分解水分子提供了能量,提供了更多的电子和氢离子。

    Light Energy to Chemical Energy
    ::轻光能源变化学能源

    Excited electrons that have absorbed light energy are unstable. However, the highly organized electron carrier molecules embedded in chloroplast membranes order the flow of these electrons, directing them through chains (ETCs). At each transfer, small amounts of energy released by the electrons are captured and put to work or stored. Some is also lost as heat with each transfer, but overall the light reactions are extremely efficient at capturing light energy and transforming it into chemical energy.
    ::吸收了光能的兴奋电子是不稳定的,然而,嵌入氯板膜中的高度有组织的电子载体分子命令这些电子流动,引导它们通过链条(ETCs)运行。在每次转移时,电子释放的少量能量都会被捕获并投入使用或储存。有些也随着每次转移的热量而消失,但总体而言,光反应在捕捉光能并将其转化为化学能量方面极为高效。

    Two sequential transport chains harvest the energy of excited electrons.
    ::两条相继运输链收获兴奋电子的能量。

    (1) First, they pass down an ETC, which captures their energy and uses it to pump hydrogen ions by into the thylakoids . These concentrated ions store potential energy by forming a chemiosmotic or – a higher concentration of both positive charge and hydrogen inside the thylakoid than outside. The gradient formed by the H + ions is known as a chemiosmotic gradient . Picture this energy buildup of H + as a dam holding back a waterfall. Like water flowing through a hole in the dam, hydrogen ions “slide down” their concentration gradient through a which acts as both ion channel and enzyme. As they flow, the ion channel/enzyme ATP synthase uses their energy to chemically bond a phosphate group to ADP, making ATP .
    :伤心1) 首先,它们传递了一种ETC,它捕捉了它们的能量,并用它将氢离子注入甲状腺,这些集中的离子通过形成一种化学反应或——在甲状腺内,正电荷和氢的浓度高于外表——将潜在能量储存起来。H+离子形成的梯度被称为化学反应梯度。想象H+的这种能量积聚作为阻挡瀑布的水坝。就像流经大坝一个洞的水,氢离子“滑落”其浓度梯度通过一个既作为离子通道又作为酶的电流。随着它们流动,离子通道/酶ATP合成酶利用它们的能量将磷酸盐组与ADP进行化学联系,使ATP成为ATP。

    (2) Light re-energizes the electrons, and they travel down a second electron transport chain (ETC), eventually bonding hydrogen ions to NADP + to form a more stable energy storage molecule, NADPH . NADPH is sometimes called “hot hydrogen,” and its energy and hydrogen atoms will be used to help build sugar in the second stage of photosynthesis.
    :伤心2) 光能重新激活电子,它们沿着第二个电子运输链(ETC)运行,最终将氢离子连接到NADP+,形成一个更稳定的能源储存分子NADPH,NADPH有时被称为“热氢”,其能量和氢原子将被用来帮助在光合作用第二阶段建造糖。

    NADPH and ATP molecules now store the energy from excited electrons – energy which was originally sunlight – in chemical bonds . Thus chloroplasts, with their orderly arrangement of pigments, enzymes, and electron transport chains, transform light energy into chemical energy. The first stage of photosynthesis – light-dependent reactions or simply light reactions – is complete.
    ::NADPH和ATP分子现在将兴奋电子 — — 最初是阳光的能源 — — 的能量储存在化学链中。 因此,叶片随着色素、酶和电子运输链的有序安排,将光能转化为化学能源。 光合作用的第一个阶段 — — 光依赖反应或光反应 — — 是完整的。

     

     

     

     

     

    Summary
    ::摘要

    • The light reactions capture energy from sunlight, which they change to chemical energy that is stored in molecules of NADPH and ATP.
      ::光反应从阳光中捕捉到能量,它们转变为化学能量,储存在NADPH和ATP的分子中。
    • The light reactions also release oxygen gas as a waste product.
      ::光反应还释放氧气作为废物。

    Review
    ::回顾

    1. Summarize what happens during the light reactions of photosynthesis.
      ::总结光合作用光反应时发生的情况。
    2. What is the chemiosmotic gradient?
      ::什么是化学梯度?
    3. Explain the role of the first electron transport chain in the formation of ATP during the light reactions of photosynthesis.
      ::解释第一个电子运输链在光合作用光反应时在ATP形成中的作用。