📚 IB & Edexcel Biology: Cell Structure Key Points | IB与Edexcel生物：细胞结构考点精讲
Welcome to this comprehensive revision guide on cell structure, tailored for both IB and Edexcel Biology students. Understanding the architecture of cells is fundamental, as it underpins every physiological process and forms the basis of many exam questions. From the lipid bilayer to the intricate endomembrane system, mastering these concepts will boost your confidence and performance.
欢迎阅读这篇专为IB和Edexcel生物学生设计的细胞结构综合复习指南。理解细胞的结构是根本，它支撑着所有生理过程，也是许多考题的基础。从脂双层到复杂的内膜系统，掌握这些概念将提升你的自信心和考试成绩。
Published by TutorHao | Biology Revision Series | aleveler.com
1. Cell Theory & Its Modern Interpretation | 细胞学说及其现代诠释
Cell theory states that all living organisms are composed of one or more cells, the cell is the basic unit of life, and all cells arise from pre-existing cells. Modern biology has extended this to include that energy flow occurs within cells and that hereditary information is passed on during cell division.
细胞学说指出，所有生物由一个或多个细胞组成，细胞是生命的基本单位，且所有细胞都来自已有细胞。现代生物学将其延伸为：能量流动发生在细胞内，遗传信息通过细胞分裂传递。
A typical light microscope resolves structures down to about 200 nm. Electron microscopes achieve resolution below 1 nm, allowing visualisation of organelles.
典型光学显微镜可分辨约200 nm的结构。电子显微镜分辨率可达1 nm以下，能够观察到细胞器。
2. Prokaryotic vs Eukaryotic Cells | 原核与真核细胞对比
Prokaryotic cells (e.g. bacteria and archaea) lack a membrane-bound nucleus and membrane-bound organelles. Their DNA is a circular chromosome located in the nucleoid region, and they possess 70S ribosomes. Many have a peptidoglycan cell wall, a capsule, pili, and flagella.
原核细胞（如细菌和古菌）没有膜包被的细胞核及膜包被的细胞器。其DNA为环状染色体，位于拟核区，拥有70S核糖体。许多具有肽聚糖细胞壁、荚膜、菌毛和鞭毛。
Eukaryotic cells (protists, fungi, plants, animals) contain a true nucleus, membrane-bound organelles, and 80S ribosomes. Their DNA is linear and packaged with histones into chromosomes. The cytoplasm is filled with a complex endomembrane system and a cytoskeleton.
真核细胞（原生生物、真菌、植物、动物）含有真正的细胞核、膜包被的细胞器以及80S核糖体。其DNA为线性，与组蛋白结合成染色体。细胞质中充满复杂的内膜系统和细胞骨架。
| Feature | Prokaryote | Eukaryote |
|---|---|---|
| Nucleus | Absent | Present |
| DNA | Circular, plasmid | Linear, histone-bound |
| Ribosomes | 70S | 80S |
| Membrane-bound organelles | None | Many |
| Cell wall | Peptidoglycan | Cellulose (plants), chitin (fungi) |
| Size | 1-10 µm | 10-100 µm |
3. The Plasma Membrane & Fluid Mosaic Model | 细胞膜与流动镶嵌模型
The plasma membrane is a phospholipid bilayer with embedded proteins, cholesterol (in animal cells), and glycocalyx. Phospholipids have hydrophilic heads facing outward and hydrophobic tails inward, creating a semi-permeable barrier.
细胞膜是由磷脂双分子层构成，其中嵌有蛋白质、胆固醇（动物细胞）和糖萼。磷脂的亲水头部朝外，疏水尾部朝内，形成半透性屏障。
The fluid mosaic model describes the membrane as a dynamic structure: lipids and proteins move laterally, giving fluidity, while the ‘mosaic’ refers to the patchwork of different proteins. Functions include transport, cell recognition, and signalling.
流动镶嵌模型将膜描述为动态结构：脂质和蛋白质可以侧向移动，赋予流动性，“镶嵌”指不同蛋白质的拼图状分布。其功能包括运输、细胞识别和信号传导。
Integral proteins span the membrane; peripheral proteins attach to the surface. Glycoproteins and glycolipids form the glycocalyx, essential for cell-to-cell communication and adhesion.
整合蛋白贯穿膜；外周蛋白附着于表面。糖蛋白和糖脂构成糖萼，对细胞通讯和粘附至关重要。
4. Nucleus & Genetic Material | 细胞核与遗传物质
The nucleus is enclosed by a double membrane (nuclear envelope) with nuclear pores that regulate molecular traffic. Inside, chromatin (DNA + histones) resides, and the nucleolus synthesises ribosomal RNA (rRNA) and assembles ribosome subunits.
细胞核由双层膜（核膜）包围，核孔调控分子进出。内部有染色质（DNA+组蛋白），核仁合成核糖体RNA（rRNA）并组装核糖体亚基。
During cell division, chromatin condenses into distinct chromosomes. The nucleus maintains genetic integrity and orchestrates gene expression. In prokaryotes, the nucleoid does not have a membrane.
细胞分裂时，染色质凝聚为清晰的染色体。细胞核维持遗传完整性并调控基因表达。在原核生物中，拟核没有膜包被。
Ribosomes assembled in the nucleolus are exported via nuclear pores. The outer nuclear membrane is often continuous with the rough endoplasmic reticulum.
在核仁中组装的核糖体经核孔输出。外核膜常与粗面内质网相连。
5. Endomembrane System: ER, Golgi, Vesicles | 内膜系统：内质网、高尔基体、囊泡
The endomembrane system includes the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vesicles, and the plasma membrane. It works together to synthesise, modify, package, and transport lipids and proteins.
内膜系统包括核膜、内质网（ER）、高尔基体、溶酶体、囊泡和细胞膜。它们协同工作，合成、修饰、包装并运输脂质和蛋白质。
Rough ER has ribosomes on its surface; it folds and modifies proteins. Smooth ER lacks ribosomes, synthesises lipids, metabolises carbohydrates, and detoxifies drugs.
粗面内质网表面有核糖体，负责蛋白质的折叠和修饰。光面内质网无核糖体，合成脂质、代谢碳水化合物并解毒药物。
The Golgi apparatus receives vesicles from the ER, further modifies proteins (e.g. glycosylation), sorts them, and dispatches them in vesicles to their destinations: secretion, plasma membrane, or lysosomes.
高尔基体接收来自内质网的囊泡，进一步修饰蛋白质（如糖基化），分选并通过囊泡运送至目的地：分泌、细胞膜或溶酶体。
6. Mitochondria & Chloroplasts: Energy Conversion | 线粒体与叶绿体：能量转换
Mitochondria are double-membrane organelles; the inner membrane is highly folded into cristae to increase surface area for oxidative phosphorylation. The matrix contains enzymes for the Krebs cycle and mitochondrial DNA (mtDNA) and ribosomes.
线粒体是双层膜细胞器；内膜向内折叠成嵴，增大了氧化磷酸化的表面积。基质含有三羧酸循环的酶、线粒体DNA（mtDNA）和核糖体。
Chloroplasts, found in plants and algae, also have a double membrane and internal thylakoids stacked into grana. The stroma contains enzymes for the Calvin cycle, DNA, and ribosomes. Chlorophyll captures light energy.
叶绿体存在于植物和藻类中，也具有双层膜，内部有类囊体堆叠成基粒。基质含有卡尔文循环的酶、DNA和核糖体。叶绿素捕捉光能。
Both organelles are believed to have originated from endosymbiotic prokaryotes — supported by their own DNA, 70S ribosomes, and double membranes.
这两种细胞器被认为起源于内共生的原核生物——证据包括它们拥有自己的DNA、70S核糖体和双层膜。
7. Ribosomes & Protein Synthesis | 核糖体与蛋白质合成
Ribosomes are non-membranous particles composed of rRNA and proteins. They consist of a large and a small subunit. Eukaryotic ribosomes are 80S, while prokaryotic, mitochondrial, and chloroplast ribosomes are 70S.
核糖体是由rRNA和蛋白质组成的无膜颗粒，包括大亚基和小亚基。真核生物核糖体为80S，原核生物、线粒体和叶绿体核糖体为70S。
They translate mRNA into polypeptides in the cytoplasm (free ribosomes) or on the rough ER (bound ribosomes). The 70S ribosome difference makes them targets for certain antibiotics.
它们在细胞质中（游离核糖体）或粗面内质网上（附着核糖体）将mRNA翻译成多肽。70S核糖体的差异使其成为某些抗生素的靶点。
Many ribosomes simultaneously translating a single mRNA form a polysome, improving efficiency.
多个核糖体同时翻译一条mRNA形成多聚核糖体，提高效率。
8. Cytoskeleton: Microtubules, Microfilaments, Intermediate Filaments | 细胞骨架
The cytoskeleton provides structural support, facilitates movement, and organises organelles. Three main types exist: microtubules, microfilaments (actin filaments), and intermediate filaments.
细胞骨架提供结构支持，促进运动并组织细胞器。主要有三种：微管、微丝（肌动蛋白丝）和中间丝。
Microtubules are hollow tubes of tubulin; they maintain cell shape, form the spindle during mitosis, and serve as tracks for motor proteins (kinesin, dynein). They are also the core of cilia and flagella (9+2 arrangement).
微管是由微管蛋白构成的空心管；维持细胞形状，在有丝分裂时形成纺锤体，并作为马达蛋白（驱动蛋白、动力蛋白）的轨道。它们也是纤毛和鞭毛的核心（9+2排列）。
Microfilaments (actin) are involved in muscle contraction, amoeboid movement, and cytokinesis (cleavage furrow). Intermediate filaments provide tensile strength and anchor organelles.
微丝（肌动蛋白）参与肌肉收缩、变形运动和胞质分裂（分裂沟）。中间丝提供抗拉强度并锚定细胞器。
9. Cell Wall & Extracellular Matrix | 细胞壁与细胞外基质
Plant cells have a rigid cell wall made of cellulose, hemicellulose, and pectin. It provides structural support, prevents excessive water uptake, and maintains shape. Fungal cell walls contain chitin; bacterial cell walls contain peptidoglycan.
植物细胞具有由纤维素、半纤维素和果胶构成的刚性细胞壁。它提供结构支持，防止过度吸水并维持形状。真菌细胞壁含几丁质，细菌细胞壁含肽聚糖。
Animal cells lack a cell wall but secrete an extracellular matrix (ECM) rich in collagen, fibronectin, and proteoglycans. The ECM influences cell adhesion, migration, and differentiation.
动物细胞没有细胞壁，但分泌富含胶原蛋白、纤连蛋白和蛋白聚糖的细胞外基质（ECM）。ECM影响细胞粘附、迁移和分化。
Plasmodesmata in plant cells and gap junctions in animal cells allow direct communication between adjacent cells.
植物细胞的胞间连丝和动物细胞的间隙连接使相邻细胞能够直接通讯。
10. Specialised Cell Structures: Cilia, Flagella, Microvilli | 特化细胞结构：纤毛、鞭毛、微绒毛
Cilia and flagella are microtubule-based projections. Cilia are numerous and short, beating in coordination to move fluid (e.g. in the trachea). Flagella are longer and usually fewer, propelling cells (e.g. sperm). Both have a 9+2 axoneme pattern of microtubules.
纤毛和鞭毛是基于微管的突起。纤毛数量多且短，协调摆动以移动液体（如气管中）。鞭毛更长且通常较少，推动细胞运动（如精子）。两者均具有9+2微管轴丝模式。
Microvilli are actin-filament-supported finger-like extensions of the plasma membrane that vastly increase surface area for absorption, prominent in the small intestine and kidney tubules.
微绒毛是由肌动蛋白丝支撑的质膜指状突起，极大增加了吸收表面积，在小肠和肾小管中尤为突出。
A basal body anchors cilia and flagella, structurally similar to a centriole (9+0 triplet arrangement).
纤毛和鞭毛由基体锚定，其结构类似于中心粒（9+0三联体排列）。
11. Microscopy & Measuring Cells | 显微镜与细胞测量
IB and Edexcel exams frequently test your ability to calculate magnification, actual size, or image size using the formula:
Magnification = Image size ÷ Actual size
Always convert units to the same scale (mm, µm, nm). Remember: 1 mm = 1000 µm; 1 µm = 1000 nm.
IB和Edexcel考试经常考查你使用公式计算放大倍数、实际大小或图像大小的能力：
放大倍数 = 图像大小 ÷ 实际大小
务必统一单位（mm、µm、nm）。记住：1 mm = 1000 µm；1 µm = 1000 nm。
A stage micrometer and an eyepiece graticule are used to calibrate and measure specimens. Ensure you know how to draw labelled diagrams and calculate scale bars.
使用镜台测微尺和目镜测微尺来校准和测量标本。确保你知道如何绘制标注图并计算比例尺。
Light microscopes can visualise living cells; transmission electron microscopes (TEM) reveal internal ultrastructure; scanning electron microscopes (SEM) show 3D external surfaces.
光学显微镜可观察活细胞；透射电子显微镜（TEM）显示内部超微结构；扫描电子显微镜（SEM）展示三维外表面。
12. Common Exam Questions & Top Tips | 常见考题与高分技巧
Expect questions comparing prokaryotic and eukaryotic cells, labelling organelle functions, explaining membrane structure, and solving magnification problems. Command terms like ‘describe’, ‘explain’, and ‘compare’ signal the depth required.
预计会出现比较原核与真核细胞、标注细胞器功能、解释膜结构以及解决放大倍数问题的题目。指令词如“描述”、“解释”和“比较”提示了所需的深度。
Draw clear, labelled diagrams even when not explicitly asked — they can earn additional marks. Use annotative arrows, not just lines. Practice conversions between mm, µm, and nm until they become second nature.
即使题目未明确要求，也画出清晰标注的图示——这能帮你赢得额外分数。使用带注释的箭头，而不仅仅是线条。反复练习mm、µm和nm之间的换算，直到熟练自如。
Revise the endosymbiotic theory evidences: mitochondria and chloroplasts have double membranes, circular DNA, 70S ribosomes, and divide by binary fission — all resembling prokaryotes.
复习内共生理论的证据：线粒体和叶绿体具有双层膜、环状DNA、70S核糖体，并通过二元分裂繁殖——这些特征都与原核生物相似。
Manage your time: allocate 1 mark per minute in exams. For 6-mark questions, structure your answer with bullet points or a logical sequence, covering all assessment objectives.
管理好时间：考试中每1分分配1分钟。对于6分题，用要点或逻辑顺序组织答案，覆盖所有评估目标。
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