5.7 Respiration: Key Exam Points | 5.7 呼吸作用考点突破

📚 5.7 Respiration: Key Exam Points | 5.7 呼吸作用考点突破

Respiration is a fundamental metabolic pathway that releases energy from organic molecules, primarily glucose, to drive cellular activities. In your exam, you need to master the stages of aerobic respiration (glycolysis, link reaction, Krebs cycle, oxidative phosphorylation) as well as anaerobic pathways, ATP yields, respiratory quotients, and practical applications. This revision guide breaks down every essential concept with paired English–Chinese explanations to help you achieve top marks.

呼吸作用是一条基础代谢途径，它从葡萄糖等有机分子中释放能量以驱动细胞活动。在考试中，你需要掌握有氧呼吸的各个阶段（糖酵解、连接反应、三羧酸循环、氧化磷酸化）以及无氧途径、ATP产量、呼吸商和实际应用。这篇复习指南通过中英文对照讲解每一个核心概念，帮助你冲击高分。

1. Overview of Respiration | 呼吸作用概述

Respiration is the enzymatic breakdown of organic substrates to release chemical energy in the form of ATP. It occurs in all living cells and can be classified as aerobic (requiring oxygen) or anaerobic (without oxygen).

呼吸作用是通过酶催化分解有机底物，以ATP形式释放化学能的过程。它发生在所有活细胞中，可分为有氧呼吸（需要氧气）和无氧呼吸（不需要氧气）。

The overall equation for aerobic respiration is often summarised as:

有氧呼吸的总方程式通常概括为：

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP)

In reality, respiration is a multi‑step process where glucose is oxidised in a controlled manner, and the free energy is used to phosphorylate ADP into ATP. ATP then serves as the immediate energy currency for cellular work.

实际上，呼吸作用是一个多步骤的过程，葡萄糖在其中被逐步氧化，释放的自由能用于将ADP磷酸化为ATP。ATP随后充当细胞活动的即时能量货币。

2. Glycolysis | 糖酵解

Glycolysis takes place in the cytoplasm and does not require oxygen. It is the first stage of both aerobic and anaerobic respiration. One molecule of glucose (a 6‑carbon sugar) is converted into two molecules of pyruvate (3C).

糖酵解发生在细胞质中，不需要氧气。它是有氧呼吸和无氧呼吸的第一阶段。一分子葡萄糖（六碳糖）被转化为两分子丙酮酸（三碳化合物）。

Energy is invested first: two ATP molecules are used to phosphorylate glucose, producing fructose‑1,6‑bisphosphate. This phosphorylation makes glucose more reactive and traps it inside the cell.

首先投入能量：使用两个ATP分子将葡萄糖磷酸化，生成果糖‑1,6‑二磷酸。这一磷酸化使葡萄糖更具反应活性，并将其限制在细胞内。

The hexose bisphosphate is split into two molecules of triose phosphate (3‑carbon). Each triose phosphate is then oxidised by the removal of hydrogen (dehydrogenation), with NAD⁺ acting as the hydrogen acceptor to form reduced NADH.

六碳糖二磷酸被裂解成两分子磷酸丙糖（三碳）。然后每个磷酸丙糖通过脱氢作用被氧化，NAD⁺作为氢受体形成还原型NADH。

Substrate‑level phosphorylation occurs, where phosphate groups are transferred directly to ADP to form ATP. Overall, 4 ATP molecules are produced per glucose, but because 2 ATP were used in the phosphorylation stage, the net gain is 2 ATP.

底物水平磷酸化发生，磷酸基团直接从底物转移到ADP以生成ATP。总体上，每分子葡萄糖产生4个ATP，但由于在磷酸化阶段消耗了2个ATP，净增益为2个ATP。

The net products of glycolysis per glucose are: 2 ATP (net), 2 NADH, and 2 pyruvate.

每分子葡萄糖经糖酵解的净产物是：2 ATP（净）、2 NADH和2丙酮酸。

Glucose + 2NAD⁺ + 2ADP + 2Pᵢ → 2 Pyruvate + 2NADH + 2H⁺ + 2ATP + 2H₂O

3. Link Reaction | 连接反应

The link reaction occurs in the mitochondrial matrix once pyruvate has entered the mitochondrion. Each pyruvate molecule is decarboxylated (a carboxyl group is removed as CO₂) and dehydrogenated (hydrogen is removed).

连接反应发生在线粒体基质中，丙酮酸进入线粒体后即发生。每个丙酮酸分子被脱羧（脱去羧基生成CO₂）和脱氢（去除氢）。

The remaining 2‑carbon acetyl group combines with coenzyme A, forming acetyl coenzyme A (acetyl‑CoA). The hydrogen removed is accepted by NAD⁺, producing reduced NADH.

剩下的二碳乙酰基与辅酶A结合，形成乙酰辅酶A。脱去的氢被NAD⁺接受，生成还原型NADH。

No ATP is made directly in this step. Since two pyruvate molecules are produced from one glucose, the link reaction occurs twice per glucose, yielding 2 acetyl‑CoA, 2 CO₂ and 2 NADH.

此步骤不直接生成ATP。由于一分子葡萄糖产生两分子丙酮酸，连接反应每分子葡萄糖发生两次，产生2乙酰辅酶A、2 CO₂和2 NADH。

Pyruvate + NAD⁺ + CoA → Acetyl‑CoA + CO₂ + NADH + H⁺

4. Krebs Cycle (Citric Acid Cycle) | 三羧酸循环（柠檬酸循环）

The Krebs cycle takes place in the mitochondrial matrix. Acetyl‑CoA (2C) combines with oxaloacetate (4C) to form citrate (6C). Coenzyme A is released and can be reused in the link reaction.

三羧酸循环发生在线粒体基质中。乙酰辅酶A（2碳）与草酰乙酸（4碳）结合生成柠檬酸（6碳）。辅酶A被释放并可重复用于连接反应。

Through a series of enzyme‑controlled reactions, citrate is decarboxylated and dehydrogenated. Two CO₂ molecules are released, regenerating the 4‑carbon oxaloacetate so the cycle can continue.

经过一系列酶控制的反应，柠檬酸被脱羧和脱氢。释放出两个CO₂分子，重新生成四碳草酰乙酸，使循环可以继续进行。

During one turn of the cycle, 3 NAD⁺ are reduced to NADH, 1 FAD is reduced to FADH₂, and 1 ATP is formed by substrate‑level phosphorylation (in the form of GTP, quickly converted to ATP). All of this occurs in a single turn, but recall that each glucose yields two acetyl‑CoA molecules, so the cycle turns twice per glucose.

循环每运转一圈，3个NAD⁺被还原为NADH，1个FAD被还原为FADH₂，另通过底物水平磷酸化生成1个ATP（以GTP形式，迅速转化为ATP）。每分子葡萄糖产生两个乙酰辅酶A，因此循环需运转两圈。

Products per glucose (two turns): 6 NADH, 2 FADH₂, 2 ATP (substrate‑level), and 4 CO₂.

每分子葡萄糖（两圈）的产物：6 NADH、2 FADH₂、2 ATP（底物水平）、4 CO₂。

5. Oxidative Phosphorylation | 氧化磷酸化

Oxidative phosphorylation occurs on the inner mitochondrial membrane. The reduced coenzymes NADH and FADH₂ are re‑oxidised, passing their electrons to the electron transport chain (ETC).

氧化磷酸化发生在线粒体内膜上。还原型辅酶NADH和FADH₂被重新氧化，将电子传递给电子传递链。

As electrons move through a series of protein complexes (I, II, III, IV), energy released is used to pump protons (H⁺) from the matrix into the intermembrane space, creating an electrochemical gradient.

电子通过一系列蛋白质复合体（I、II、III、IV）传递时，释放的能量被用来将质子（H⁺）从基质泵入膜间隙，形成电化学梯度。

Protons flow back into the matrix through ATP synthase, a channel that uses the flow (chemiosmosis) to phosphorylate ADP + Pᵢ into ATP. This is known as oxidative phosphorylation because oxygen is the final electron acceptor, combining with electrons and protons to form water.

质子通过ATP合酶流回基质，该通道利用质子流（化学渗透）将ADP + Pᵢ磷酸化为ATP。这被称为氧化磷酸化，因为氧气是最终电子受体，与电子和质子结合生成水。

If oxygen is absent, the ETC halts, and no ATP can be made via this route – hence the need for anaerobic respiration in some organisms. In eukaryotes, each NADH typically yields about 2.5 ATP and each FADH₂ yields about 1.5 ATP, although exact numbers depend on shuttle systems.

如果缺乏氧气，电子传递链停止，因此无法通过此途径生成ATP——这就是某些生物需要进行无氧呼吸的原因。在真核生物中，每个NADH通常生成约2.5个ATP，每个FADH₂生成约1.5个ATP，尽管确切数值取决于穿梭系统。

6. Anaerobic Respiration | 无氧呼吸

When oxygen is limited, some cells can respire anaerobically using only glycolysis. The priority is to re‑oxidise the NADH produced in glycolysis back to NAD⁺, so that glycolysis can continue and produce at least some ATP.

当氧气有限时，一些细胞可以通过仅使用糖酵解进行无氧呼吸。首要任务是将在糖酵解中产生的NADH重新氧化为NAD⁺，从而使糖酵解得以继续并至少产生一些ATP。

In animal cells (e.g. human muscle cells during vigorous exercise), pyruvate is reduced to lactate (lactic acid) by the enzyme lactate dehydrogenase. NADH donates its hydrogen, regenerating NAD⁺.

在动物细胞中（如剧烈运动时的人体肌肉细胞），丙酮酸经由乳酸脱氢酶催化被还原为乳酸。NADH提供氢，使NAD⁺得以再生。

In yeast and some bacteria, pyruvate is decarboxylated to ethanal and then reduced to ethanol, also regenerating NAD⁺. This ethanol fermentation also produces CO₂.

在酵母和某些细菌中，丙酮酸被脱羧生成乙醛，然后被还原为乙醇，同时再生NAD⁺。这种乙醇发酵还会释放CO₂。

The net ATP yield from anaerobic respiration is only the 2 ATP from glycolysis per glucose. Anaerobic respiration is less efficient but provides a quick energy supply when oxygen is scarce.

无氧呼吸的净ATP产量仅为每分子葡萄糖从糖酵解获得的2个ATP。无氧呼吸效率较低，但能在缺氧时快速提供能量。

Animal: Pyruvate + NADH → Lactate + NAD⁺
Yeast: Pyruvate → Ethanal + CO₂ → Ethanol + NAD⁺

7. ATP Yield and Efficiency | ATP产量与效率

The theoretical maximum ATP yield from one glucose molecule in aerobic respiration is often quoted as 38 ATP for prokaryotes, but in eukaryotes the total is approximately 30–32 ATP. This lower number reflects the energy cost of transporting NADH from glycolysis into the mitochondria.

有氧呼吸中一分子葡萄糖的理论最大ATP产量在教材中常被引述为原核生物38个ATP，但在真核生物中总数约为30–32个ATP。这个较低的数字反映了将糖酵解产生的NADH运送进线粒体的能量消耗。

A typical breakdown in eukaryotes is: glycolysis (net 2 ATP, 2 NADH → later yields ~3–5 ATP depending on shuttle), link reaction (2 NADH → ~5 ATP), Krebs cycle (2 ATP substrate‑level, 6 NADH → ~15 ATP, 2 FADH₂ → ~3 ATP). Adding these gives around 30–32 ATP.

真核生物中的典型分解如下：糖酵解（净2 ATP，2 NADH后续生成约3–5 ATP），连接反应（2 NADH生成约5 ATP），三羧酸循环（底物水平2 ATP，6 NADH生成约15 ATP，2 FADH₂生成约3 ATP）。合计约30–32 ATP。

In contrast, anaerobic respiration yields only 2 ATP per glucose, illustrating the importance of oxygen for maximal energy harvesting. While the efficiency of aerobic respiration is about 32–34% of the total energy available, the rest is released as heat to maintain body temperature in warm‑blooded organisms.

相比之下，无氧呼吸每分子葡萄糖仅产生2个ATP，这突显了氧气对于最大限度获取能量的重要性。有氧呼吸的效率约为可利用能量的32%至34%，其余以热量形式释放，用于维持恒温动物的体温。

8. Respiratory Quotient (RQ) | 呼吸商

The respiratory quotient (RQ) is the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed during respiration, measured at the same temperature and pressure.

呼吸商（RQ）是在相同温度和压力下，呼吸作用中产生的二氧化碳体积与消耗的氧气体积之比。

RQ = CO₂ produced ÷ O₂ consumed

The RQ value gives clues about the type of respiratory substrate being used. For carbohydrates, RQ = 1.0 (equal volumes of CO₂ and O₂). For lipids, RQ ≈ 0.7 (less O₂ needed per CO₂ released). For proteins, RQ is about 0.9, though it varies depending on amino acid composition.

RQ值可提示被利用的呼吸底物类型。碳水化合物RQ = 1.0（CO₂和O₂体积相等）。脂质RQ ≈ 0.7（每释放CO₂所需氧气较少）。蛋白质RQ约为0.9，但会因氨基酸组成而异。

When carbohydrates are converted to fat (e.g. in overfeeding), RQ can exceed 1.0 because the synthesis of fat from carbohydrate releases extra CO₂. Examiners often ask you to calculate RQ from respirometer data or to deduce the substrate from RQ values.

当碳水化合物转化为脂肪（如过度喂养）时，RQ可能超过1.0，因为从碳水化合物合成脂肪会释放额外的CO₂。考官常要求根据呼吸计数据计算RQ，或根据RQ值推断底物。

9. Respiratory Substrates | 呼吸底物

The main respiratory substrates are carbohydrates (mainly glucose), lipids (fatty acids and glycerol), and proteins. All can be respired, but they enter the respiratory pathway at different points.

主要的呼吸底物包括碳水化合物（主要是葡萄糖）、脂质（脂肪酸和甘油）以及蛋白质。它们都可以被呼吸，但进入呼吸途径的节点不同。

Glucose is the primary fuel for most cells. Lipids yield more energy per gram than carbohydrates because they are more reduced and contain less water. Before respiration, lipids are hydrolysed to glycerol and fatty acids; glycerol can be converted to triose phosphate and enter glycolysis, while fatty acids undergo β‑oxidation to form acetyl‑CoA.

葡萄糖是大多数细胞的主要燃料。脂质每克提供的能量比碳水化合物更多，因为它们更为还原且含水量少。呼吸前，脂质被水解为甘油和脂肪酸；甘油可转化为磷酸丙糖进入糖酵解，脂肪酸则通过β‑氧化生成乙酰辅酶A。

Proteins are generally used only when carbohydrate and fat reserves are depleted. They are first deaminated (removal of amino groups) and the carbon skeletons are converted into pyruvate, acetyl‑CoA, or Krebs cycle intermediates. The amino groups are converted to urea for excretion.

蛋白质通常只在碳水化合物和脂肪储备耗尽时使用。它们首先被脱氨（去除氨基），碳

Published by TutorHao | Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）