📚 Respiration – IGCSE CIE Biology Exam Tips | 呼吸作用考点精讲
Respiration is one of the most fundamental life processes. It is the series of chemical reactions that releases energy from food molecules such as glucose, and this energy is used to power all the activities of living cells. For IGCSE CIE Biology, you must be able to write word and chemical equations, compare aerobic and anaerobic respiration, explain the role of ATP, describe practical investigations, and apply your knowledge to real-world processes like bread-making and muscle fatigue. This revision guide breaks down every key point in precise, exam-focused detail.
呼吸作用是最基本的生命过程之一。它是一系列从葡萄糖等食物分子中释放能量的化学反应，这些能量用于驱动活细胞的所有活动。针对IGCSE CIE生物考试，你必须能够书写文字方程式和化学方程式，比较有氧呼吸和无氧呼吸，解释ATP的作用，描述实验探究，并将知识应用到面包制作和肌肉疲劳等实际过程中。这份复习指南以精准、紧扣考点的细节分解了每一个关键知识点。
1. What Is Respiration? | 什么是呼吸作用?
Respiration is the process by which living cells release energy from organic molecules, primarily glucose. It is an exothermic reaction that occurs in every living cell continuously. The energy released is stored in a molecule called ATP (adenosine triphosphate), which acts as the immediate energy currency of the cell.
呼吸作用是活细胞从有机分子(主要是葡萄糖)中释放能量的过程。这是一个发生在每一个活细胞中且持续进行的放热反应。释放的能量储存在一种叫做ATP(三磷酸腺苷)的分子中，它充当细胞的即时能量货币。
It is crucial not to confuse respiration with breathing (ventilation). Breathing is the physical movement of air into and out of the lungs, while respiration is a chemical process that takes place inside cells. In IGCSE exams, you may be asked to distinguish between the two.
至关重要的是不要将呼吸作用与呼吸(通气)混淆。呼吸是空气进出肺部的物理运动，而呼吸作用是在细胞内部发生的化学过程。在IGCSE考试中，你可能会被要求区分这两者。
The main substrates for respiration are glucose and other nutrients, but glucose is the most common fuel.
呼吸作用的主要底物是葡萄糖和其他营养物质，但葡萄糖是最常见的燃料。
Energy released is used for active transport, muscle contraction, cell division, maintaining body temperature (in mammals), and building large molecules from smaller ones.
释放的能量用于主动运输、肌肉收缩、细胞分裂、维持体温(哺乳动物)以及由小分子合成大分子。
2. Aerobic Respiration | 有氧呼吸
Aerobic respiration requires oxygen. It takes place in the mitochondria of cells and produces a large amount of ATP. The complete breakdown of glucose releases carbon dioxide and water, with a high yield of energy.
有氧呼吸需要氧气。它发生在线粒体中，产生大量的ATP。葡萄糖的完全分解会释放二氧化碳和水，并伴随高能量产出。
The word equation for aerobic respiration is:
有氧呼吸的文字方程式为：
glucose + oxygen → carbon dioxide + water (+ energy released as ATP)
葡萄糖 + 氧气 → 二氧化碳 + 水 (+ 以ATP形式释放的能量)
The balanced chemical equation using symbols is:
用符号表示的平衡化学方程式为：
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy / ATP)
In IGCSE CIE exams, you must be able to recall both the word and the symbol equations. Note that the energy released is not a chemical substance but is transferred to ATP molecules. The process involves many enzyme-controlled steps inside the mitochondria, but for the exam you only need to state the overall reaction.
在IGCSE CIE考试中，你必须能够记住文字方程式和符号方程式。注意，释放的能量不是一种化学物质，而是转移到ATP分子中。该过程涉及线粒体内许多酶控制的步骤，但在考试中你只需陈述总反应。
3. Anaerobic Respiration in Animals | 动物无氧呼吸
When oxygen is in short supply, animal cells can switch to anaerobic respiration. This is a temporary measure that allows glycolysis to continue and produces a small amount of ATP without using oxygen. In animals (including humans), anaerobic respiration breaks down glucose into lactic acid.
当氧气供应不足时，动物细胞可以转为无氧呼吸。这是一种临时措施，使得糖酵解能够继续，并在不使用氧气的情况下产生少量ATP。在动物(包括人类)中，无氧呼吸将葡萄糖分解为乳酸。
The word equation is:
文字方程式为：
glucose → lactic acid (+ some energy released as ATP)
葡萄糖 → 乳酸 (+ 部分以ATP形式释放的能量)
In symbols, it is often simplified to:
用符号通常简化为：
C₆H₁₂O₆ → 2C₃H₆O₃ (+ energy)
Lactic acid build-up in muscles causes cramp and fatigue. After exercise, oxygen is needed to break down the lactic acid into carbon dioxide and water in the liver – this extra oxygen is called the oxygen debt. You must be able to explain how muscle cells respire anaerobically during vigourous exercise when oxygen delivery can't keep up with demand.
肌肉中乳酸的积累会导致痉挛和疲劳。运动后，需要氧气将乳酸在肝脏中分解为二氧化碳和水——这部分额外的氧气被称为氧债。你必须能够解释在高强度运动中，当氧气供应无法满足需求时，肌肉细胞如何进行无氧呼吸。
4. Anaerobic Respiration in Plants & Yeast | 植物与酵母的无氧呼吸
Plants and microorganisms such as yeast can also respire anaerobically. In yeast and many plant tissues, anaerobic respiration produces ethanol and carbon dioxide instead of lactic acid. This is often referred to as fermentation.
植物和酵母等微生物也可以进行无氧呼吸。在酵母和许多植物组织中，无氧呼吸产生乙醇和二氧化碳而非乳酸。这通常被称为发酵。
Word equation:
文字方程式：
glucose → ethanol + carbon dioxide (+ some energy released as ATP)
葡萄糖 → 乙醇 + 二氧化碳 (+ 部分以ATP形式释放的能量)
Chemical equation:
化学方程式：
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (+ energy)
Notice that carbon dioxide is released in this type of anaerobic respiration, unlike in animals. This fact is critical when designing or interpreting experiments investigating respiration. For example, yeast producing CO₂ can be detected by limewater turning milky, even in the absence of oxygen.
请注意，与动物不同，这种类型的无氧呼吸会释放二氧化碳。在设计或解读探究呼吸作用的实验时，这一事实至关重要。例如，即使在无氧条件下，酵母产生的CO₂也可以通过石灰水变浑浊来检测。
5. Comparing Aerobic and Anaerobic Respiration | 有氧与无氧呼吸比较
The table below summarises the key differences and the one important similarity you need to know for the exam.
下表总结了你需要为考试掌握的关键区别和一个重要的相似点。
| Feature | 特点 | Aerobic Respiration | 有氧呼吸 | Anaerobic Respiration | 无氧呼吸 |
|---|---|---|
| Oxygen required | 是否需要氧气 | Yes | 是 | No | 否 |
| Site in cell | 细胞内场所 | Mitochondria | 线粒体 | Cytoplasm only | 仅细胞质 |
| Products in animals | 动物产物 | CO₂ + H₂O | 二氧化碳+水 | Lactic acid | 乳酸 |
| Products in yeast/plants | 酵母/植物产物 | CO₂ + H₂O | 二氧化碳+水 | Ethanol + CO₂ | 乙醇+二氧化碳 |
| Energy released | 释放的能量 | Large amount (approx. 38 ATP) | Small amount (2 ATP) |
| Degree of glucose breakdown | 葡萄糖分解程度 | Complete | 完全 | Incomplete | 不完全 |
Similarity: Both processes begin with glycolysis in the cytoplasm and produce ATP. Glucose is the starting substrate in both.
相似点：两种过程都从细胞质中的糖酵解开始并产生ATP。葡萄糖是两者的起始底物。
Exam tip: Always specify which type of organism you are referring to when writing the anaerobic products. Saying 'anaerobic respiration produces lactic acid' is only correct for animals; plants and yeast produce ethanol and CO₂ instead.
考试技巧：在书写无氧呼吸产物时，务必说明你指的是哪种生物。如果说“无氧呼吸产生乳酸”仅对动物正确；植物和酵母则产生乙醇和二氧化碳。
6. The Role of ATP | ATP的作用
ATP (adenosine triphosphate) is the energy-carrying molecule used in all living cells. When ATP is broken down into ADP (adenosine diphosphate) and an inorganic phosphate (Pᵢ), energy is released. This energy is directly used to drive energy-requiring processes in the cell.
ATP(三磷酸腺苷)是所有活细胞中使用的能量载体分子。当ATP分解为ADP(二磷酸腺苷)和一个无机磷酸(Pᵢ)时，能量被释放。这些能量直接用于驱动细胞内的需能过程。
ATP → ADP + Pᵢ (+ energy for cellular work)
The synthesis of ATP from ADP and Pᵢ happens during respiration, and this is how energy released from glucose is captured in a usable form. You do not need to know the detailed structure of ATP for IGCSE CIE, but you must understand its role as an 'energy currency'.
从ADP和Pᵢ合成ATP的过程发生在呼吸作用中，这就是葡萄糖释放的能量被捕获为可用形式的方式。IGCSE CIE并不要求你了解ATP的详细结构，但你必须理解它作为“能量货币”的作用。
Uses of ATP include muscle contraction, active transport across membranes, synthesis of proteins and other large molecules, and cell division. Without ATP production from respiration, these activities would stop.
ATP的用途包括肌肉收缩、跨膜主动运输、蛋白质及其他大分子的合成、以及细胞分裂。如果没有呼吸作用产生的ATP，这些活动将会停止。
7. Investigating Respiration: Heat Production | 探究呼吸作用：产热
Respiration is an exothermic reaction, and the heat produced can be measured experimentally. A classic investigation uses germinating seeds in a vacuum flask with a thermometer. As the seeds respire aerobically, they release heat, causing the temperature inside the flask to rise.
呼吸作用是一种放热反应，可以通过实验测量产生的热量。一个经典的探究实验将萌发的种子放入带有温度计的保温瓶中。当种子进行有氧呼吸时释放热量，导致瓶内温度升高。
Control experiments should use dead, boiled seeds (washed in disinfectant) to prove that the heating is due to living processes and not microbial decay. This demonstrates the importance of a control for a valid comparison.
对照实验应使用死的、煮沸过的种子(并用消毒剂清洗)，以证明升温来自生命活动过程而非微生物腐烂。这体现了设立对照以进行有效比较的重要性。
In IGCSE exam questions, you may be asked to suggest how to improve the reliability of this experiment – for example, by repeating with multiple flasks or insulating the apparatus further.
在IGCSE考试问题中，你可能会被要求建议如何提高该实验的可靠性——例如，通过用多个烧瓶重复实验或进一步隔热设备。
8. Investigating Respiration: Carbon Dioxide Production | 探究呼吸作用：二氧化碳产生
Carbon dioxide is a product of both aerobic respiration and anaerobic respiration in yeast. The standard test for CO₂ is limewater, which turns from clear to cloudy/milky when CO₂ is bubbled through it. Another indicator is hydrogencarbonate indicator, which changes from red-orange to yellow in the presence of CO₂.
二氧化碳是有氧呼吸和酵母无氧呼吸的产物。检测CO₂的标准方法是石灰水，当CO₂通过时，石灰水会从澄清变为浑浊/乳白色。另一种指示剂是碳酸氢盐指示剂，它在CO₂存在时会从红橙色变为黄色。
A typical class experiment involves connecting a flask containing respiring organisms (e.g. germinating seeds or small invertebrates) to a tube of limewater. Air is drawn through the apparatus slowly to carry CO₂ into the limewater. A second setup with dead organisms acts as the control and should produce little or no colour change.
一个典型的课堂实验是将装有呼吸生物(如萌发的种子或小型无脊椎动物)的烧瓶连接到一个装有石灰水的试管。空气缓慢地通过装置，将CO₂带入石灰水中。第二个使用死生物的设置作为对照，应产生极少量或没有颜色变化。
If using yeast, the same setup can be used for anaerobic respiration by covering the yeast suspension with a layer of oil to exclude oxygen. CO₂ produced will still turn limewater milky, confirming that anaerobic respiration in yeast releases CO₂.
如果使用酵母，可以通过在酵母悬液上覆盖一层油以隔绝氧气，来检测其无氧呼吸。产生的CO₂仍会使石灰水变浑浊，从而确认酵母的无氧呼吸释放CO₂。
9. Investigating Respiration: Oxygen Uptake | 探究呼吸作用：氧气消耗
To measure oxygen consumption during respiration, a respirometer is used. This apparatus typically contains organisms (such as maggots or germinating seeds) in a sealed tube connected to a coloured liquid in a capillary tube. As the organisms take up oxygen, the liquid moves along the tube, and the distance moved indicates the volume of oxygen consumed.
为了测量呼吸作用中的耗氧量，需要使用呼吸计。该设备通常将生物(如蛆虫或萌发的种子)放置在一个密封管中，并连接到一根毛细管内的有色液体。当生物吸收氧气时，液体会沿管子移动，移动的距离表示消耗的氧气体积。
Soda lime or potassium hydroxide solution is added to absorb the CO₂ produced; otherwise, the volume of gas would not change because CO₂ is released at approximately the same rate as O₂ is taken up. By absorbing CO₂, any decrease in gas volume is due solely to O₂ consumption.
需要加入碱石灰或氢氧化钾溶液来吸收产生的CO₂；否则，由于CO₂的释放速率与O₂的吸收速率大致相同，气体体积不会变化。通过吸收CO₂，任何气体体积的减少都完全归因于O₂的消耗。
For anaerobic respiration, the apparatus would show no change in volume because no oxygen is taken up. This can be used to distinguish between the two modes of respiration in yeast when layered with oil.
对于无氧呼吸，装置不会显示体积变化，因为没有氧气被消耗。这可以用来在酵母被油层覆盖时区分其两种呼吸模式。
10. Applications of Anaerobic Respiration | 无氧呼吸的应用
Anaerobic respiration in yeast is exploited in the food industry for baking and brewing. In bread-making, yeast ferments sugars in the dough, producing CO₂ bubbles that cause the dough to rise and giving bread its light, spongy texture. The ethanol evaporates during baking.
酵母的无氧呼吸在食品工业中被用于烘焙和酿造。在面包制作中，酵母发酵面团中的糖类，产生CO₂气泡，使面团膨胀，从而赋予面包轻盈、松软的质地。乙醇在烘烤过程中蒸发。
In brewing, yeast respires anaerobically to convert sugars in fruit juice or grain extract into ethanol, producing alcoholic drinks such as wine and beer. The amount of alcohol produced depends on the yeast strain and the availability of sugar.
在酿造中，酵母进行无氧呼吸，将果汁或谷物提取物中的糖转化为乙醇，从而生产出葡萄酒和啤酒等酒精饮料。产生的酒精量取决于酵母菌株和糖的可利用性。
Another application is the production of biogas, where organic waste is broken down by microorganisms in anaerobic conditions to release methane, which can be used as fuel. This process links to the carbon cycle and sustainable energy resources, which may appear in ecosystem questions.
另一个应用是生产沼气，即在厌氧条件下，有机废物被微生物分解，释放出甲烷作为燃料使用。这一过程与碳循环和可持续能源资源相联系，可能会出现在生态系统相关问题中。
11. Key Exam Tips & Common Misconceptions | 重要考试技巧与常见误区
Do not confuse respiration with breathing. Respiration is a chemical reaction that releases energy; breathing is the physical process of moving air in and out.
不要混淆呼吸作用与呼吸。呼吸作用是释放能量的化学反应；呼吸是空气进出的物理过程。
Remember that anaerobic respiration in animals produces lactic acid, NOT ethanol and CO₂. In yeast and plants, anaerobic respiration produces ethanol and CO₂ – know which is which.
记住动物的无氧呼吸产生乳酸，而不是乙醇和CO₂。在酵母和植物中，无氧呼吸产生乙醇和CO₂——清楚区分二者。
ATP is the energy currency; energy is not produced as a separate substance. Always mention that energy is released and transferred to ATP.
ATP是能量货币；能量不是作为分离的物质产生的。始终要提到能量被释放并转移给ATP。
When describing respirometer experiments, always mention the role of soda lime for absorbing CO₂. Without this step, you cannot measure O₂ uptake reliably.
在描述呼吸计实验时，一定要提及碱石灰吸收CO₂的作用。没有这一步，就无法可靠地测量O₂消耗。
In practical investigations, always set up a control (e.g. boiled/dead organisms) to prove that the observed effect is due to respiration and not another factor.
在实验探究中，始终设置对照组(如煮沸/死亡的生物)，以证明观察到的效应来自呼吸作用而非其他因素。
Aerobic respiration releases more energy per glucose molecule than anaerobic respiration. Be prepared to explain why: incomplete breakdown of glucose in anaerobic conditions.
有氧呼吸每分子葡萄糖比无氧呼吸释放更多能量。准备好解释原因：无氧条件下葡萄糖的不完全分解。
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