📚 IGCSE CCEA Biology: Cell Structure | IGCSE CCEA 生物：细胞结构 考点精讲
Cells are the fundamental units of life, and understanding their structure is crucial for every IGCSE CCEA Biology student. This revision guide covers animal cells, plant cells, bacteria, fungi, protoctists and viruses – highlighting key organelles, functions and comparisons that often appear in CCEA examinations. Use this article to consolidate your knowledge of cell structure, microscope calculations and the principles of cell organisation.
细胞是生命的基本单位，理解其结构对每一位 IGCSE CCEA 生物学习者都至关重要。这篇复习指南涵盖了动物细胞、植物细胞、细菌、真菌、原生生物和病毒，着重讲解常出现在 CCEA 考试中的关键细胞器、功能及比较。用这篇文章来巩固你在细胞结构、显微镜计算和细胞组织原理方面的知识。
1. The Cell Theory | 细胞学说
Cell theory states that all living organisms are composed of cells, the cell is the basic unit of structure and function, and all cells arise from pre-existing cells. This principle underpins modern biology and was developed through the work of scientists such as Hooke, Schleiden, Schwann and Virchow.
细胞学说指出，所有生物体都由细胞构成，细胞是结构和功能的基本单位，并且所有细胞都来源于已有的细胞。这一原理是现代生物学的基础，由胡克、施莱登、施旺和魏尔啸等科学家的研究发展而来。
In CCEA examinations, you may be asked to explain how cell theory applies to unicellular and multicellular organisms, and to discuss exceptions such as viruses – which are not considered living cells.
在 CCEA 考试中，你可能会被要求解释细胞学说如何适用于单细胞和多细胞生物，并讨论例外情况，例如病毒——它们不被视为活细胞。
2. Animal Cell Ultrastructure | 动物细胞超微结构
A typical animal cell contains a nucleus, cytoplasm, cell membrane, mitochondria, ribosomes and may include small temporary vacuoles. The nucleus holds genetic material (DNA) and controls cellular activities; it is surrounded by a nuclear membrane with pores. The cytoplasm is a jelly-like matrix where chemical reactions occur. The cell membrane, composed of phospholipids and proteins, is selectively permeable, controlling the movement of substances.
典型的动物细胞包含细胞核、细胞质、细胞膜、线粒体、核糖体，并可能含有小型的临时液泡。细胞核容纳遗传物质（DNA）并控制细胞活动；它由带有核孔的核膜包围。细胞质是发生化学反应的胶状基质。由磷脂和蛋白质组成的细胞膜具有选择透过性，控制物质进出。
Mitochondria are oval-shaped organelles with a double membrane; the inner membrane folds into cristae to increase surface area for aerobic respiration, releasing energy in the form of ATP. Ribosomes are tiny structures, bound to the rough endoplasmic reticulum or free in the cytoplasm, where protein synthesis takes place.
线粒体是具有双层膜的椭圆形细胞器；内膜向内折叠形成嵴，以增加有氧呼吸的表面积，释放 ATP 形式的能量。核糖体是微小的结构，附着在粗面内质网上或游离于细胞质中，蛋白质合成在此进行。
An animal cell lacks a cell wall and chloroplasts, and its vacuoles are small and numerous rather than one large central vacuole.
动物细胞没有细胞壁和叶绿体，其液泡小而多，而不是一个大中央液泡。
3. Plant Cell Ultrastructure | 植物细胞超微结构
Plant cells share many organelles with animal cells but possess three distinctive features: a cellulose cell wall, a large permanent vacuole and chloroplasts (in photosynthetic tissues). The cell wall is made of cellulose fibres, provides structural support and shape, and is fully permeable to water and dissolved substances. The large central vacuole contains cell sap (a solution of salts and sugars) and helps maintain turgor pressure, keeping the cell rigid.
植物细胞与动物细胞共有许多细胞器，但具有三个独特特征：纤维素细胞壁、一个大型永久液泡和叶绿体（在光合组织内）。细胞壁由纤维素纤维构成，提供结构支撑和形状，对水及溶解物质完全通透。大中央液泡含有细胞液（盐与糖的溶液），并有助于维持膨压，使细胞保持坚挺。
Chloroplasts are lens-shaped organelles containing the green pigment chlorophyll. They are the site of photosynthesis, where light energy is converted into chemical energy. Each chloroplast has a double membrane and an internal system of thylakoid membranes stacked into grana, suspended in the stroma.
叶绿体是含有绿色色素叶绿素的透镜状细胞器。它们是光合作用的场所，在此光能被转化为化学能。每个叶绿体具有双层膜，内部类囊体膜系统堆叠成基粒，悬浮于基质中。
Ribosomes, mitochondria, endoplasmic reticulum and the Golgi apparatus are also present, performing the same fundamental roles as in animal cells.
核糖体、线粒体、内质网和高尔基体同样存在，执行与动物细胞中相同的基本功能。
4. Key Comparisons Between Animal and Plant Cells | 动物细胞与植物细胞的关键比较
CCEA often requires students to tabulate or describe differences. The table below summarises the main contrasts.
CCEA 常要求学生列表或描述差异。下表总结了主要对比。
| Feature / 特征 | Animal Cell / 动物细胞 | Plant Cell / 植物细胞 |
| Cell wall / 细胞壁 | Absent / 无 | Present (cellulose) / 有（纤维素） |
| Chloroplasts / 叶绿体 | Absent / 无 | Present in green parts / 在绿色部分有 |
| Vacuole / 液泡 | Small, temporary / 小，临时性 | Large, permanent / 大，永久性 |
| Shape / 形状 | Irregular / 不规则 | Regular (turgid) / 规则（膨压） |
| Carbohydrate storage / 碳水化合物储存 | Glycogen / 糖原 | Starch / 淀粉 |
Remember that both cell types possess nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Explaining how the structures relate to their functions is essential for earning higher marks.
记住，两种细胞类型都拥有细胞核、细胞质、细胞膜、线粒体和核糖体。解释结构如何与其功能相关联是获得高分的关键。
5. Bacterial Cell Structure | 细菌细胞结构
Bacteria are prokaryotes, meaning their cells lack a true nucleus and membrane-bound organelles. The genetic material is a single circular chromosome of DNA, free in the cytoplasm, often accompanied by small rings of DNA called plasmids. A bacterial cell is surrounded by a cell wall made of peptidoglycan (not cellulose) and a cell membrane.
细菌是原核生物，意味着它们的细胞没有真正的细胞核和膜包裹的细胞器。遗传物质是一个单一的环状 DNA 染色体，游离于细胞质中，通常还有称为质粒的小环状 DNA 相伴。细菌细胞由肽聚糖（非纤维素）构成的细胞壁和细胞膜所包围。
Many bacteria have a slime capsule outside the wall for protection and to help them adhere to surfaces. Some possess flagella for locomotion, which are long protein filaments that rotate. Ribosomes (70S, smaller than the 80S ribosomes of eukaryotes) are present for protein synthesis, but mitochondria, chloroplasts and nuclear envelope are absent.
许多细菌在细胞壁外有一层黏液荚膜，用于保护并帮助附着在表面上。一些细菌拥有用于运动的鞭毛，它们是旋转的蛋白质长丝。存在核糖体（70S，比真核生物的 80S 核糖体小）进行蛋白质合成，但无线粒体、叶绿体和核膜。
In CCEA, you might need to label a diagram of a bacterium, identify features and contrast it with eukaryotic cells.
在 CCEA 中，你可能需要标注细菌示意图、识别其特征并与真核细胞进行对比。
6. Fungal Cell: Yeast | 真菌细胞：酵母菌
Yeast is a unicellular fungus studied in IGCSE CCEA Biology. The yeast cell has a cell wall made of chitin, not cellulose or peptidoglycan. It possesses a true nucleus (eukaryotic), cytoplasm, a cell membrane, mitochondria and vacuoles, but lacks chloroplasts as fungi are heterotrophic.
酵母是 IGCSE CCEA 生物中研究的单细胞真菌。酵母细胞具有由几丁质（而非纤维素或肽聚糖）组成的细胞壁。它拥有真正的细胞核（真核生物）、细胞质、细胞膜、线粒体和液泡，但缺乏叶绿体，因为真菌是异养生物。
Yeast stores carbohydrate as glycogen and can respire aerobically or anaerobically. Many yeast cells reproduce by budding, where a small outgrowth from the parent cell enlarges and eventually separates.
酵母以糖原形式储存碳水化合物，并能进行有氧或无氧呼吸。许多酵母细胞通过出芽繁殖，即从母细胞长出的一个小突起逐渐增大并最终分离。
In the exam, you should be able to compare yeast cells with plant and bacterial cells, focusing on the cell wall composition and nutritional mode.
在考试中，你应该能够比较酵母细胞与植物细胞及细菌细胞，重点关注细胞壁组成和营养方式。
7. Protoctist: Amoeba | 原生生物：变形虫
Amoeba is a single-celled eukaryotic organism belonging to the kingdom Protoctista. It lives in water and has a flexible cell membrane with no cell wall, allowing it to change shape. The cytoplasm is divided into an outer clear ectoplasm and an inner granular endoplasm. It contains a nucleus, contractile vacuole (for osmoregulation), food vacuoles and mitochondria.
变形虫是一种属于原生生物界的单细胞真核生物。它生活在水中，具有无细胞壁的柔性细胞膜，使其能改变形状。细胞质分为外部透明的外质和内部颗粒状的内质。它包含细胞核、伸缩泡（用于渗透调节）、食物泡和线粒体。
Amoeba moves and captures prey by extending temporary projections called pseudopodia (false feet). It engulfs food particles by phagocytosis, forming a food vacuole where digestion occurs.
变形虫通过伸出称为伪足的临时突起进行运动和捕捉猎物。它通过吞噬作用吞食食物颗粒，形成食物泡，消化便在泡内发生。
This organism exemplifies how a single cell can perform all life processes, making it a common exam example for protoctists.
这一生物体展示了单一细胞如何执行所有生命过程，因此成为原生生物中常见的考试例子。
8. Viruses: Acellular Structures | 病毒：非细胞结构
Viruses are not classified as living cells. They are small particles consisting of genetic material (DNA or RNA) enclosed in a protein coat called a capsid, sometimes with a lipid envelope. They lack cytoplasm, organelles, enzymes for metabolism, and cannot reproduce independently – they must infect a host cell to replicate.
病毒未被归类为活细胞。它们是微小颗粒，由包裹在称为衣壳的蛋白质外壳中的遗传物质（DNA 或 RNA）组成，有时具有脂质包膜。它们缺乏细胞质、细胞器、用于新陈代谢的酶，并且不能独立繁殖——它们必须感染宿主细胞才能复制。
The CCEA specification expects you to explain why viruses are not considered living: they do not carry out the seven life processes (MRS GREN) outside the host. However, you should recognise components like the capsid and genetic core in a labelled diagram.
CCEA 大纲要求你解释为什么病毒不被视为生物：它们在宿主外不执行七种生命过程（MRS GREN）。然而，你应能在标注图中识别衣壳和遗传核心等组成部分。
Examples include the tobacco mosaic virus (rod-shaped) and human immunodeficiency virus (spherical with envelope).
例子包括烟草花叶病毒（杆状）和人类免疫缺陷病毒（球形，具包膜）。
9. Magnification and Size Calculations | 放大倍率与大小计算
Calculating magnification or actual size of a specimen is a key practical skill in CCEA. The formula is:
计算标本的放大倍率或实际大小是 CCEA 中的一项关键实验技能。公式为：
Magnification = Image size ÷ Actual size
放大倍率 = 图像尺寸 ÷ 实际尺寸
Always ensure that the units of image size and actual size are the same before calculating. Commonly used units are millimetres (mm), micrometres (µm) and nanometres (nm). Remember the conversions: 1 mm = 1000 µm; 1 µm = 1000 nm.
计算前务必确保图像尺寸和实际尺寸的单位一致。常用单位是毫米 (mm)、微米 (µm) 和纳米 (nm)。记住换算关系：1 mm = 1000 µm；1 µm = 1000 nm。
For example, if an image of a cell is 5 mm (5000 µm) and the actual cell is 20 µm, the magnification = 5000 ÷ 20 = ×250. Many CCEA exam questions require rearranging the equation and showing working.
例如，若一张细胞图像为 5 mm（5000 µm），而实际细胞为 20 µm，则放大倍率 = 5000 ÷ 20 = ×250。许多 CCEA 考题要求变形公式并展示计算过程。
10. Levels of Organisation and Specialised Cells | 组织层次与特化细胞
In multicellular organisms, cells of similar structure and function group together to form tissues; tissues working together form organs; and organs cooperating for a common function build organ systems. CCEA expects you to apply this hierarchy, e.g. muscle cell → muscle tissue → heart → circulatory system.
在多细胞生物中，结构和功能相似的细胞聚集形成组织；共同工作的组织形成器官；为共同功能而协作的器官构建器官系统。CCEA 要求你应用这一层级关系，例如：肌肉细胞 → 肌肉组织 → 心脏 → 循环系统。
Specialised cells are adapted to perform specific roles. Example: a red blood cell has a biconcave disc shape, no nucleus and contains haemoglobin to maximise oxygen transport. A root hair cell in plants has a large surface area and thin walls to absorb water and minerals efficiently. Be prepared to explain how the structure of at least three specialised cells relates to their function.
特化细胞适应于执行特定的功能。例如：红细胞呈双凹圆盘状，无细胞核，并含有血红蛋白，以最大限度地运输氧气。植物根毛细胞具有很大的表面积和薄壁，以高效吸收水分和矿物质。请准备好解释至少三种特化细胞的结构如何与其功能相关。
CCEA exam papers frequently include unfamiliar cells and ask students to deduce functions from structural features – practising this skill is invaluable.
CCEA 试卷常出现陌生细胞，要求学生根据结构特征推断功能——练习这一技能十分宝贵。
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