📚 IGCSE Edexcel Science: Cell Structure and Organisation | IGCSE Edexcel 科学：细胞结构与组织
All living organisms are made of cells. The cell is the smallest unit that can carry out all life processes, from exchanging gases to releasing energy from food. By studying cell structure and organisation, you can explain how the building blocks of life work together to keep an organism alive.
所有生物体都由细胞构成。细胞是能够完成全部生命活动的最小单位，例如进行气体交换、从食物中释放能量。通过学习细胞结构与组织，你可以解释生命的基本单位如何协同工作，从而维持生物体的生命活动。
1. Prokaryotic and Eukaryotic Cells | 原核细胞与真核细胞
Cells are divided into two broad groups: prokaryotic cells and eukaryotic cells. Prokaryotic cells, such as bacteria, do not have a true nucleus or membrane-bound organelles. Eukaryotic cells, such as animal and plant cells, have a distinct nucleus and membrane-bound organelles including mitochondria and chloroplasts.
细胞分为两大类：原核细胞与真核细胞。原核细胞如细菌，没有真正的细胞核，也没有膜包被的细胞器。真核细胞如动物细胞和植物细胞，具有清晰可见的细胞核，并含有线粒体、叶绿体等膜包被的细胞器。
- Prokaryotic cells are usually smaller and simpler.
原核细胞通常更小、结构更简单。 - Eukaryotic cells have a nucleus; prokaryotic cells do not.
真核细胞有细胞核，原核细胞没有。 - Bacteria have a cell wall made of peptidoglycan, not cellulose.
细菌的细胞壁由肽聚糖组成，而不是纤维素。 - Eukaryotic cells contain mitochondria; prokaryotic cells generally do not.
真核细胞含有线粒体，原核细胞通常没有。
2. Animal Cell Organelles | 动物细胞的细胞器
An animal cell contains several organelles, each with a specific function. You need to be able to label a typical animal cell and recall the role of each part.
动物细胞含有多种细胞器，每一种都有特定功能。你需要能够标注典型动物细胞的结构，并记住各部分的机能。
| Organelle (English) | 细胞器（中文） | Function (English) | 功能（英文） | 功能（中文） |
|---|---|---|
| Nucleus | 细胞核 | Contains DNA; controls cell activities | 含有DNA；控制细胞活动 |
| Cytoplasm | 细胞质 | Site of most chemical reactions | 大多数化学反应进行的场所 |
| Cell membrane | 细胞膜 | Controls what enters and leaves | 控制物质进出细胞 |
| Mitochondria | 线粒体 | Aerobic respiration occurs here | 有氧呼吸在此发生 |
| Ribosomes | 核糖体 | Synthesis of proteins | 合成蛋白质 |
3. Plant Cell Structures | 植物细胞的特殊结构
Plant cells have all the organelles of animal cells, but they also contain three extra structures: a cellulose cell wall, chloroplasts, and a permanent vacuole. These structures support the plant and allow it to make food by photosynthesis.
植物细胞拥有动物细胞的所有细胞器，但还额外含有三种结构：纤维素细胞壁、叶绿体和永久性液泡。这些结构支撑植物体，并使其能通过光合作用制造食物。
- Cell wall: made of cellulose, supports the cell and prevents it from bursting.
细胞壁：由纤维素构成，支撑细胞并防止细胞破裂。 - Chloroplasts: contain chlorophyll, which absorbs light energy for photosynthesis.
叶绿体：含有叶绿素，吸收光能用于光合作用。 - Permanent vacuole: filled with cell sap, helping to keep the cell turgid.
永久性液泡：充满细胞液，有助于维持细胞的膨压。
4. Comparing Animal and Plant Cells | 动物细胞与植物细胞的比较
A common exam question asks you to compare animal and plant cells. You should remember that plant cells have a cell wall, chloroplasts and a large vacuole, while animal cells do not.
常见的考试题会要求你比较动物细胞和植物细胞。你需要记住：植物细胞有细胞壁、叶绿体和大液泡，而动物细胞没有这些结构。
| Structure | 结构 | Animal Cell | 动物细胞 | Plant Cell | 植物细胞 |
|---|---|---|
| Nucleus | 细胞核 | Present | 有 | Present | 有 |
| Cell membrane | 细胞膜 | Present | 有 | Present | 有 |
| Cell wall | 细胞壁 | Absent | 无 | Present | 有 |
| Chloroplasts | 叶绿体 | Absent | 无 | Present | 有 |
| Permanent vacuole | 永久性液泡 | Absent | 无 | Present | 有 |
5. Specialised Animal Cells | 特化的动物细胞
Specialised cells have particular structures that help them carry out one specific function. In animals, examples include sperm cells, red blood cells, nerve cells and muscle cells.
特化细胞具有特殊的结构，帮助它们完成某一特定功能。在动物中，例子包括精子细胞、红细胞、神经细胞和肌肉细胞。
- Sperm cell: has a tail for swimming, many mitochondria for energy, and enzymes to digest egg membrane.
精子细胞：有尾巴用于游动，含大量线粒体提供能量，并有酶消化卵细胞膜。 - Red blood cell: biconcave shape increases surface area for oxygen uptake; contains haemoglobin.
红细胞：双凹形状增加吸收氧气的表面积；含有血红蛋白。 - Nerve cell: long axon and dendrites to transmit electrical impulses quickly.
神经细胞：长轴突和树突，快速传导电冲动。 - Muscle cell: contains many mitochondria for energy and protein filaments for contraction.
肌肉细胞：含大量线粒体供能，并有蛋白质细丝用于收缩。
6. Specialised Plant Cells | 特化的植物细胞
Plant cells also become specialised for different roles. You should be familiar with root hair cells, xylem vessels, phloem sieve tubes and palisade cells.
植物细胞也会发生特化以承担不同功能。你需要熟悉根毛细胞、木质部导管、韧皮部筛管和栅栏细胞。
- Root hair cell: long extension increases surface area for water and mineral uptake.
根毛细胞：长突起增大表面积，利于吸收水分和矿物质。 - Xylem vessel: no living contents; thick walls with spirals of lignin for support and water transport.
木质部导管：没有活的内含物；厚壁并有木质素螺旋，用于支撑和运输水分。 - Phloem sieve tube: sieve plates allow dissolved sugars to flow through the plant.
韧皮部筛管：筛板允许溶解的糖类在植物体内流动。 - Palisade cell: packed with chloroplasts for maximum photosynthesis near the leaf surface.
栅栏细胞：富含叶绿体，在叶表附近最大程度进行光合作用。
7. Levels of Organisation | 组织的层次
In multicellular organisms, similar cells work together in groups. These groups form tissues, tissues form organs, and organs work together in organ systems.
在多细胞生物体中，相似的细胞协同工作形成群体。这些群体构成组织，组织构成器官，器官协同工作形成器官系统。
Cells → Tissues → Organs → Organ Systems → Organism
细胞 → 组织 → 器官 → 器官系统 → 生物体
- Cell: basic unit of life, e.g. muscle cell.
细胞：生命的基本单位，如肌肉细胞。 - Tissue: a group of similar cells working together, e.g. muscle tissue.
组织：一群相似细胞协同工作，如肌肉组织。 - Organ: made of different tissues performing a specific function, e.g. heart.
器官：由不同组织组成并执行特定功能，如心脏。 - Organ system: several organs working together, e.g. the circulatory system.
器官系统：多个器官协同工作，如循环系统。
8. Magnification and Cell Size | 放大倍数与细胞大小
Microscopy questions often require you to calculate magnification, actual size, or image size. The formula is:
显微镜题目经常要求你计算放大倍数、实际大小或图像大小。公式如下：
Magnification = Image size ÷ Actual size
放大倍数 = 图像大小 ÷ 实际大小
For example, if an image is 50 mm long and the actual cell is 0.5 mm long, then the magnification is 50 ÷ 0.5 = 100×.
例如，如果图像长度为 50 mm，而细胞实际长度为 0.5 mm，则放大倍数 = 50 ÷ 0.5 = 100×。
Always check units: 1 mm = 1000 μm. If necessary, convert before dividing.
始终检查单位：1 mm = 1000 μm。如有必要，先换算再进行除法。
9. Common Exam Pitfalls and Revision Tips | 常见考试易错点与复习建议
Many students lose marks on cell structure questions due to small errors. Here are some tips to avoid common mistakes.
很多学生在细胞结构题目上因为小错误丢分。以下是一些避免常见错误的建议。
- Do not forget units in magnification calculations.
计算放大倍数时不要漏写单位。 - Do not confuse the cell wall with the cell membrane.
不要把细胞壁和细胞膜混淆。 - Remember that plant cells also have mitochondria and ribosomes.
记住植物细胞也有线粒体和核糖体。 - Learn at least one example of each specialised cell.
至少记住每种特化细胞的一个例子。 - Practice drawing and labelling cells from memory.
练习凭记忆绘制并标注细胞图。
10. Summary | 总结
Cell structure and organisation is a foundation topic for iGCSE Edexcel Science. You should be able to describe the differences between prokaryotic and eukaryotic cells, label animal and plant cells, explain adaptations of specialised cells, and arrange cells into tissues, organs and systems.
细胞结构与组织是 iGCSE Edexcel 科学的基础主题。你需要能够描述原核细胞与真核细胞的区别，标注动物细胞和植物细胞，解释特化细胞的适应性结构，并将细胞按层次排列为组织、器官和系统。
Once you master these ideas, you will find it easier to understand later topics such as transport in animals and plants, respiration and photosynthesis.
一旦掌握这些概念，你就会发现后续主题，如动植物体内的运输、呼吸作用和光合作用，都更容易理解了。
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