Cell Organelles: IB and Edexcel Biology Complete Guide | IB Edexcel 生物：细胞器考点精讲

📚 Cell Organelles: IB and Edexcel Biology Complete Guide | IB Edexcel 生物：细胞器考点精讲

Cell organelles are the specialised subunits within a cell that perform specific functions, much like organs in a body. Understanding their structure and interactions is essential for both IB and Edexcel Biology, as questions frequently test your ability to link organelle function to processes such as protein synthesis, energy conversion and cell division. This revision guide walks you through every key organelle, explains the evidence for endosymbiosis, compares prokaryotic and eukaryotic cells, and highlights common pitfalls in exams.

细胞器是细胞内执行特定功能的特化亚基，就像身体中的器官一样。理解它们的结构和相互作用对 IB 和 Edexcel 生物考试都至关重要，因为考题经常考查你将细胞器功能与蛋白质合成、能量转换和细胞分裂等过程联系起来的能力。这份复习指南将带你梳理每一个关键细胞器，解释内共生的证据，比较原核细胞与真核细胞，并指出考试中常见的易错点。

1. Overview of Cell Organelles | 细胞器总览

Eukaryotic cells contain membrane-bound organelles that compartmentalise metabolic reactions, increasing efficiency and preventing harmful interactions. The main organelles include the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, vacuoles, chloroplasts (in plants), and the cytoskeleton. Each organelle has a unique composition of lipids and proteins, and their distribution varies according to cell type and function.

真核细胞含有膜包被的细胞器，这些细胞器将代谢反应分隔开，提高了效率并防止有害的相互干扰。主要细胞器包括细胞核、线粒体、内质网、高尔基体、溶酶体、过氧化物酶体、液泡、叶绿体（植物）以及细胞骨架。每种细胞器都具有独特的脂质和蛋白质组成，其分布因细胞类型和功能而异。

Table: Major organelles and their primary roles

表：主要细胞器及其主要功能

Organelle	Primary function
Nucleus	Stores genetic material, controls gene expression
Mitochondrion	Aerobic respiration, ATP production
Chloroplast	Photosynthesis (plants, algae)
Rough ER	Protein synthesis and folding
Smooth ER	Lipid synthesis, detoxification
Golgi apparatus	Modifies, sorts and packages proteins
Lysosome	Intracellular digestion
Ribosome	Protein synthesis (translation)
Vacuole	Storage, turgor pressure

2. Nucleus: the Control Centre | 细胞核：控制中心

The nucleus is the largest organelle in most eukaryotic cells and is surrounded by a double membrane called the nuclear envelope. This envelope is studded with nuclear pores that regulate the passage of molecules such as mRNA and ribosomal subunits. Inside, chromatin (DNA wrapped around histone proteins) and the nucleolus, where ribosomal RNA is synthesised and ribosome assembly begins, can be observed.

细胞核是大多数真核细胞中最大的细胞器，由称为核膜的双层膜包裹。核膜上分布着核孔，调节 mRNA 和核糖体亚基等分子的进出。核内可以看到染色质（缠绕在组蛋白上的 DNA）以及核仁，核仁是 rRNA 合成和核糖体组装起始的场所。

During cell division, chromatin condenses into discrete chromosomes. IB exam questions often ask you to identify the nucleolus and nuclear pores in electron micrographs and to explain how the structure of the nuclear pore facilitates selective transport. Edexcel papers might ask you to describe the relationship between the nucleus and the rough ER.

在细胞分裂期间，染色质凝缩为离散的染色体。IB 考题经常要求你在电子显微镜照片中辨认核仁和核孔，并解释核孔结构如何实现选择性转运。Edexcel 的试卷可能会要求你描述细胞核与粗面内质网之间的关系。

3. Mitochondria: Powerhouse and Endosymbiosis | 线粒体：动力工厂与内共生

Mitochondria are double-membrane organelles that produce ATP via aerobic respiration. The inner membrane is folded into cristae, which increase the surface area for oxidative phosphorylation. The matrix contains enzymes for the Krebs cycle, mitochondrial DNA, and ribosomes of the 70S type – a key piece of evidence for the endosymbiotic theory.

线粒体是双层膜的细胞器，通过有氧呼吸产生 ATP。内膜折叠成嵴，增加了氧化磷酸化的表面积。基质中含有三羧酸循环所需的酶、线粒体 DNA 以及 70S 型核糖体——这是内共生理论的关键证据之一。

The endosymbiotic theory states that mitochondria evolved from aerobic bacteria that were engulfed by an ancestral eukaryotic cell. Supporting evidence includes: mitochondria have their own circular DNA, double membranes, and divide by binary fission; they also have 70S ribosomes similar to those in prokaryotes. Both IB and Edexcel specifications require you to describe this theory and the evidence for it.

内共生理论认为，线粒体是从被原始真核细胞吞噬的好氧细菌进化而来的。支持证据包括：线粒体拥有自身的环状 DNA、双层膜，并通过二分裂方式增殖；它们还含有与原核生物类似的 70S 核糖体。IB 和 Edexcel 教学大纲都要求你描述这一理论及其证据。

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP

The overall equation for aerobic respiration summarises the process that takes place partly in the cytosol and partly inside mitochondria. You should be able to locate glycolysis, the link reaction, the Krebs cycle and the electron transport chain within the cell.

有氧呼吸的总方程式总结了该过程，它部分发生在细胞质溶胶中，部分在线粒体内。你应该能够指出糖酵解、连接反应、三羧酸循环和电子传递链在细胞内的位置。

4. Chloroplasts: Photosynthesis and Endosymbiosis | 叶绿体：光合作用与内共生

Chloroplasts are found in plant cells and some algae. They have a double membrane and an internal system of thylakoid membranes arranged in stacks called grana. The stroma contains enzymes for the Calvin cycle, chloroplast DNA, and 70S ribosomes. Like mitochondria, chloroplasts are believed to have originated from a cyanobacterium via endosymbiosis.

叶绿体存在于植物细胞和一些藻类中。它们具有双层膜和内部称为类囊体的膜系统，类囊体堆叠成基粒。基质中含有卡尔文循环所需的酶、叶绿体 DNA 以及 70S 核糖体。与线粒体一样，叶绿体被认为是通过内共生起源于蓝细菌。

The light-dependent reactions occur on the thylakoid membranes, while the light-independent reactions (Calvin cycle) take place in the stroma. For exams, you must link the structure of the chloroplast to its function: the large surface area of thylakoids maximises light absorption, and the stroma compartment concentrates CO₂ fixation enzymes.

光反应发生在类囊体膜上，而暗反应（卡尔文循环）在基质中进行。考试中，你必须将叶绿体的结构与其功能联系起来：类囊体巨大的表面积最大化光吸收，基质区域则浓缩了固定 CO₂ 的酶。

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

This equation appears frequently in both IB and Edexcel papers. Be prepared to identify the organelles involved and to explain the role of chlorophyll in trapping light energy.

这个方程式经常出现在 IB 和 Edexcel 的试卷中。准备好辨认涉及的细胞器，并解释叶绿素在捕获光能中的作用。

5. Endoplasmic Reticulum and Ribosomes | 内质网与核糖体

The endoplasmic reticulum (ER) is a network of membranous tubules and sacs. Rough ER is studded with ribosomes and is the site of protein synthesis for proteins destined for secretion or membrane insertion. Ribosomes translating these proteins are directed to the ER by a signal sequence. Smooth ER lacks ribosomes and is involved in lipid synthesis, carbohydrate metabolism, and detoxification of drugs and poisons.

内质网（ER）是由膜性小管和囊泡组成的网络。粗面内质网上附着有核糖体，是合成分泌蛋白或膜蛋白的场所。翻译这些蛋白质的核糖体通过信号序列被引导到内质网。滑面内质网则没有核糖体，参与脂质合成、碳水化合物代谢以及药物和毒物的解毒。

Ribosomes themselves are not membrane-bound organelles but are essential for translation. Eukaryotic ribosomes are 80S, composed of a 60S and a 40S subunit. They can be free in the cytoplasm (synthesising cytosolic proteins) or bound to the rough ER. IB and Edexcel both expect you to distinguish between free and bound ribosomes and to give examples of proteins synthesised at each location.

核糖体本身不是膜包被的细胞器，但对翻译至关重要。真核生物的核糖体为 80S，由 60S 和 40S 亚基组成。它们可以游离在细胞质中（合成胞质蛋白），也可以结合在粗面内质网上。IB 和 Edexcel 都要求你区分游离核糖体和结合核糖体，并举例说明各自位置合成的蛋白质。

6. Golgi Apparatus and Vesicle Transport | 高尔基体与囊泡运输

The Golgi apparatus consists of flattened membranous sacs called cisternae. It receives transport vesicles from the ER at its cis face, modifies proteins (e.g., glycosylation), sorts them, and dispatches them in vesicles from the trans face to their destinations – the plasma membrane, lysosomes, or secretion outside the cell.

高尔基体由称为潴泡的扁平膜囊组成。它在顺面接收来自内质网的运输囊泡，对蛋白质进行修饰（如糖基化）、分拣，并从反面将蛋白质以囊泡形式发往目的地——质膜、溶酶体或分泌到细胞外。

Vesicle trafficking is a dynamic process involving budding, transport, and fusion. Exam questions often trace the path of a protein such as an antibody from its synthesis on ribosomes to its secretion. Remember the sequence: RER → transport vesicle → cis Golgi → trans Golgi → secretory vesicle → exocytosis.

囊泡运输是一个涉及出芽、运输和融合的动态过程。考试题常常追踪一种蛋白质（如抗体）从核糖体上合成到分泌的路径。请记住顺序：粗面内质网 → 运输囊泡 → 高尔基顺面 → 高尔基反面 → 分泌囊泡 → 胞吐作用。

7. Lysosomes and Peroxisomes | 溶酶体与过氧化物酶体

Lysosomes are membrane-bound vesicles containing hydrolytic enzymes that digest macromolecules. They function in autophagy (digesting worn-out organelles), phagocytosis (fusing with food vacuoles in immune cells), and programmed cell death. The internal pH of lysosomes is kept at ~5.0 to protect the cell if leakage occurs.

溶酶体是含有水解酶的膜包囊泡，能消化大分子。它们的功能包括自噬（消化老化的细胞器）、吞噬作用（在免疫细胞中与食物泡融合）以及程序性细胞死亡。溶酶体内部 pH 维持在约 5.0，以便在泄漏时保护细胞。

Peroxisomes are smaller organelles that contain oxidative enzymes, such as catalase, which break down fatty acids and detoxify hydrogen peroxide. They are particularly abundant in liver and kidney cells. In plant seeds, specialised peroxisomes called glyoxysomes convert stored lipids into sugars.

过氧化物酶体是较小的细胞器，含有氧化酶（如过氧化氢酶），能分解脂肪酸并解毒过氧化氢。它们在肝细胞和肾细胞中尤其丰富。在植物种子中，称为乙醛酸循环体的特殊过氧化物酶体将储存的脂质转化为糖类。

8. Vacuoles and Storage | 液泡与储存

Vacuoles are large, membrane-bound sacs found predominantly in plant cells. The central vacuole stores water, ions, sugars, pigments, and waste products. It also maintains turgor pressure, which is essential for structural support. In animal cells, vacuoles are smaller and often involved in endocytosis and exocytosis.

液泡是主要存在于植物细胞中的大型膜包囊。中央液泡储存水分、离子、糖类、色素和废物。它还维持着膨压，这对结构支持至关重要。在动物细胞中，液泡较小，通常参与胞吞和胞吐作用。

Contractile vacuoles in freshwater protists like Paramecium expel excess water to prevent lysis. IB often asks about osmoregulation in unicellular organisms, while Edexcel may incorporate vacuoles into context-based questions about plant wilting.

淡水原生动物（如草履虫）中的伸缩泡能排出多余水分以防止细胞破裂。IB 经常考查单细胞生物的渗透调节，而 Edexcel 可能将液泡融入到关于植物萎蔫的情景题中。

9. Cytoskeleton: Microtubules, Microfilaments, Intermediate Filaments | 细胞骨架：微管、微丝、中间纤维

The cytoskeleton is a dynamic network of protein filaments that provides shape, mechanical support, and intracellular transport. It consists of three main types: microtubules (made of tubulin), microfilaments (actin), and intermediate filaments (various proteins). Each type has distinct roles – microtubules form the mitotic spindle and serve as tracks for motor proteins, microfilaments drive cell movement and cytokinesis, and intermediate filaments provide tensile strength.

细胞骨架是由蛋白质纤维组成的动态网络，提供形状、机械支持和胞内运输。它主要包括三类：微管（由微管蛋白组成）、微丝（肌动蛋白）和中间纤维（多种蛋白质）。每种类型都有独特的作用——微管形成纺锤体并作为马达蛋白的轨道，微丝驱动细胞运动和胞质分裂，中间纤维则提供抗拉强度。

In IB Biology, knowledge of the cytoskeleton is required to explain processes such as muscle contraction (actin and myosin), flagella movement (microtubules in ‘9+2’ arrangement), and the movement of vesicles along microtubules. Edexcel may ask you to relate cytoskeletal elements to specialised cell structures like microvilli.

在 IB 生物中，需要运用细胞骨架的知识来解释诸如肌肉收缩（肌动蛋白和肌球蛋白）、鞭毛运动（“9+2”排列的微管）以及囊泡沿微管移动等过程。Edexcel 可能会要求你将细胞骨架成分与微绒毛等特化细胞结构联系起来。

10. Comparing Prokaryotic and Eukaryotic Cells | 原核细胞与真核细胞的比较

A classic exam question asks you to compare the ultrastructure of prokaryotes and eukaryotes. Prokaryotic cells lack a nucleus and membrane-bound organelles, have circular DNA freely in the cytoplasm, and possess 70S ribosomes. They may have a cell wall containing peptidoglycan (bacteria) and structures like pili and flagella. Eukaryotic cells, in contrast, contain a true nucleus, linear DNA with histones, 80S ribosomes, and a variety of membrane-bound organelles.

一道经典的考题要求你比较原核生物和真核生物的超微结构。原核细胞没有细胞核和膜包被的细胞器，DNA 呈环状游离在细胞质中，并具有 70S 核糖体。它们可能含有由肽聚糖（细菌）组成的细胞壁以及菌毛和鞭毛等结构。相反，真核细胞含有真正的细胞核、与组蛋白结合的线性 DNA、80S 核糖体和各种膜包被的细胞器。

Both IB and Edexcel recognise that some features overlap: prokaryotes can have infoldings of the plasma membrane analogous to cristae (mesosomes), and eukaryotes can have circular DNA in mitochondria and chloroplasts. The endosymbiotic theory helps explain these similarities.

IB 和 Edexcel 都承认有些特征是重叠的：原核生物可以有类似嵴的质膜内褶（间体），而真核生物可以在线粒体和叶绿体中存在环状 DNA。内共生理论有助于解释这些相似性。

11. Techniques to Study Organelles: Microscopy and Cell Fractionation | 研究细胞器的技术：显微镜与细胞分级分离

Electron microscopy (TEM and SEM) provides high-resolution images of organelles. Transmission electron microscopy reveals internal structures like cristae and thylakoids, while scanning electron microscopy shows surface features. IB requires you to interpret electron micrographs and relate structures to functions. Edexcel practicals may include drawing cells from microscope observations.

电子显微镜（透射电镜和扫描电镜）提供了细胞器的高分辨率图像。透射电子显微镜显示嵴和类囊体等内部结构，而扫描电子显微镜则展示表面特征。IB 要求你解读电子显微镜照片并将结构与功能联系起来。Edexcel 的实践环节可能包括根据显微镜观察画细胞图。

Cell fractionation is a technique used to isolate organelles by centrifugation at increasing speeds. The process involves homogenisation (breaking cells open), filtration, and differential centrifugation. The pellet obtained at each spin is enriched for a specific organelle: nuclei at 1,000 × g, mitochondria at 10,000 × g, and microsomes (ER fragments) at 100,000 × g. You need to explain why the process must be carried out in cold, isotonic, buffered solutions.

细胞分级分离是一种通过逐渐提高离心转速来分离细胞器的技术。该过程包括匀浆（破碎细胞）、过滤和差速离心。每次离心后得到的沉淀富含特定细胞器：1000 × g 得到细胞核，10000 × g 得到线粒体，100000 × g 得到微粒体（内质网碎片）。你需要解释为什么这一过程必须在冷、等渗、缓冲溶液中进行。

12. Exam Tips and Common Mistakes | 考试技巧与常见错误

One frequent error is using ‘S’ unit incorrectly – remember that Svedberg units are not additive, so 50S + 30S = 70S, not 80S. Also, many students confuse the terms ‘cell wall’ and ‘cell membrane’, or state that animal cells have a cell wall. Ensure you know the composition of walls in plants (cellulose), fungi (chitin), and bacteria (peptidoglycan).

一个常见错误是错误使用“S”单位——记住沉降系数不是可加的，因此 50S + 30S = 70S，而不是 80S。此外，许多学生混淆“细胞壁”和“细胞膜”，或说动物细胞有细胞壁。务必了解植物（纤维素）、真菌（几丁质）和细菌（肽聚糖）细胞壁的成分。

When describing endosymbiosis, provide specific evidence rather than claiming ‘they are similar’. Quote 70S ribosomes, circular DNA, double membranes, and binary fission. In IB extended-response questions, structure and function must always be linked – never list structures without explaining how they aid the function.

在描述内共生时，要提供具体的证据，而不是只说“它们相似”。要引用 70S 核糖体、环状 DNA、双层膜和二分裂。在 IB 拓展性回答题中，结构必须始终与功能联系起来——不要只列出结构而不解释它们如何帮助实现功能。

Finally, practise drawing and labelling organelles: a good diagram of a mitochondrion or a chloroplast with clear, ruled label lines and no arrowheads can earn marks quickly in both IB and Edexcel papers.

最后，练习绘制并标注细胞器：画一个清晰的线粒体或叶绿体示意图，用尺子引线标注且不带箭头，能在 IB 和 Edexcel 的试卷中迅速得分。

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Cell Organelles: IB and Edexcel Biology Complete Guide | IB Edexcel 生物：细胞器 考点精讲