📚 Cell Structure and Organisation | 细胞结构与组织
This article covers the essential ideas of cell structure and organisation for the Edexcel IGCSE Biology specification. Cells are the smallest units that can be said to be alive, and their structure is directly linked to their function in organisms.
本文涵盖爱德思 IGCSE 生物考纲中关于细胞结构和组织的核心知识。细胞是能够被称为“活的”最小单位，其结构直接与它们在生物体中的功能相关。
1. The Basic Components of a Cell | 细胞的基本组成
All living organisms are made of cells. Although cells vary in size and shape, they share four basic features: a cell membrane, cytoplasm, genetic material (DNA), and ribosomes. These features allow the cell to perform life processes such as respiration, nutrition, and reproduction.
所有生物体都由细胞构成。尽管细胞的大小和形状各不相同，但它们都具有四个基本特征：细胞膜、细胞质、遗传物质（DNA）和核糖体。这些特征使细胞能够进行呼吸、营养和繁殖等生命活动。
Cell membrane: controls the movement of substances in and out of the cell.
细胞膜：控制物质进出细胞。
Cytoplasm: a jelly-like material where most chemical reactions happen.
细胞质：一种胶状物质，大多数化学反应在此发生。
Genetic material (DNA): carries instructions for cell activities and inheritance.
遗传物质（DNA）：携带细胞活动和遗传的指令。
Ribosomes: tiny structures that make proteins using instructions from DNA.
核糖体：利用 DNA 的指令制造蛋白质的微小结构。
2. Animal Cells: Key Organelles | 动物细胞：关键细胞器
Animal cells contain several organelles that work together to keep the cell alive. The nucleus is the largest organelle and contains chromosomes made of DNA. Mitochondria are the site of aerobic respiration, releasing energy for the cell.
动物细胞含有多种细胞器，它们共同协作维持细胞的生存。细胞核是最大的细胞器，含有由 DNA 构成的染色体。线粒体是有氧呼吸的场所，为细胞释放能量。
Nucleus: stores DNA and controls cell division and protein synthesis.
细胞核：储存 DNA，控制细胞分裂和蛋白质合成。
Mitochondria: carry out aerobic respiration to produce ATP.
线粒体：进行有氧呼吸以产生 ATP。
Ribosomes: attach to mRNA and build polypeptide chains (proteins).
核糖体：附着在 mRNA 上，合成多肽链（蛋白质）。
Cell membrane: selectively permeable, regulates transport of substances.
细胞膜：选择透过性，调节物质的运输。
3. Plant Cells: Additional Features | 植物细胞：额外结构
Plant cells have all the organelles found in animal cells, plus three extra structures that are not present in animal cells: a cell wall, a permanent vacuole, and chloroplasts.
植物细胞拥有动物细胞中的所有细胞器，并且还额外具有三种动物细胞所没有的结构：细胞壁、永久性液泡和叶绿体。
Cell wall: made of cellulose, provides strength and support.
细胞壁：由纤维素组成，提供强度和支撑。
Vacuole: contains cell sap, helps maintain turgidity and support.
液泡：含有细胞液，有助于维持膨压和支持。
Chloroplasts: contain chlorophyll for photosynthesis; absorb light energy.
叶绿体：含有叶绿素，用于光合作用；吸收光能。
4. Differences Between Animal and Plant Cells | 动物细胞与植物细胞的区别
The table below summarises the main structural differences between animal and plant cells for the Edexcel IGCSE exam.
下表总结了爱德思 IGCSE 考试中动物细胞与植物细胞的主要结构差异。
| Feature | Animal Cell | Plant Cell |
|---|---|---|
| Cell wall | Absent | Present (cellulose) |
| Chloroplasts | Absent | Present (in green parts) |
| Vacuole | Small or temporary | Large permanent vacuole |
| Shape | Usually round/irregular | Regular/rectangular |
5. Specialised Cells: Structure and Function | 特化细胞：结构与功能
Cells differentiate to become specialised for a particular job. Their structure is closely matched to their function. Common examples in IGCSE include red blood cells, root hair cells, sperm cells, and palisade mesophyll cells.
细胞通过分化变得特化，以执行特定功能。它们的结构与功能密切相关。IGCSE 中常见的例子包括红细胞、根毛细胞、精子和栅栏叶肉细胞。
Red blood cell: biconcave disc, no nucleus, rich in haemoglobin – this increases surface area and oxygen-carrying capacity.
红细胞：双凹圆盘状，无细胞核，富含血红蛋白——这增加了表面积和携氧能力。
Root hair cell: long thin extension, large surface area – maximises water and mineral ion uptake from soil.
根毛细胞：细长的突起，表面积大——最大程度地从土壤中吸收水分和矿质离子。
Sperm cell: tail for swimming, many mitochondria for energy, acrosome (in animals) for digesting the egg membrane.
精子：有尾可游动，线粒体多提供能量，顶体（动物中）可消化卵细胞膜。
Palisade cell: packed with chloroplasts near the leaf surface – maximises light absorption for photosynthesis.
栅栏细胞：在叶表层附近排列紧密，含大量叶绿体——最大化吸收光能用于光合作用。
6. Cell Differentiation | 细胞分化
Differentiation is the process by which a cell becomes specialised to perform a specific function. In animals, most differentiation occurs during development and in certain tissues (like bone marrow stem cells), while in plants, meristem tissue remains able to differentiate throughout life.
分化是细胞转变为特化细胞以执行特定功能的过程。在动物中，大多数分化发生在发育过程中以及某些组织（如骨髓干细胞）内；而在植物中，分生组织在一生中都保持分化能力。
In the Edexcel IGCSE course, you should be able to explain that differentiation involves changes in gene expression. All cells in an organism contain the same DNA, but different genes are switched on or off in different cell types.
在爱德思 IGCSE 课程中，你需要能够解释分化涉及基因表达的改变。一个生物体中的所有细胞都含有相同的 DNA，但不同类型的细胞中，不同的基因会被开启或关闭。
7. Levels of Organisation | 组织层次
Multicellular organisms are organised in a hierarchy: cells form tissues, tissues form organs, organs form organ systems, and organ systems form the whole organism.
多细胞生物体按层级组织：细胞构成组织，组织构成器官，器官构成器官系统，器官系统构成整个生物体。
Tissue: a group of similar cells working together to perform a common function. Example: muscle tissue, xylem tissue.
组织：一群相似的细胞共同执行同一功能。例如：肌肉组织、木质部组织。
Organ: a structure made of multiple tissues working together. Example: the heart contains muscle, nerve, and blood tissues.
器官：由多种组织共同构成的结构。例如：心脏包含肌肉、神经和血液组织。
Organ system: a group of organs that work together to carry out a major body function. Example: the digestive system.
器官系统：一组器官协同完成主要身体功能。例如：消化系统。
8. Cell Size and Microscopy | 细胞大小与显微技术
Most cells are between 10 µm and 100 µm in diameter. A typical animal cell is about 20 µm, while a plant cell is often 40–100 µm. You should be able to use a light microscope to identify basic cell structures.
大多数细胞的直径在 10 µm 到 100 µm 之间。典型动物细胞约为 20 µm，而植物细胞通常为 40–100 µm。你应该能够使用光学显微镜识别基本细胞结构。
To convert units: 1 cm = 10 mm = 10,000 µ 10,000,000 nm. In calculations, use the formula magnification = image size ÷ actual size.
单位换算：1 cm = 10 mm = 10,000 µm = 10,000,000 nm。计算时使用公式：放大倍率 = 图像大小 ÷ 实际大小。
Magnification = Image size ÷ Actual size
放大倍率 = 图像大小 ÷ 实际大小
9. Prokaryotic and Eukaryotic Cells | 原核细胞与真核细胞
Eukaryotic cells (plant and animal cells) have a true nucleus containing chromosomes and membrane-bound organelles. Prokaryotic cells (bacteria) have no nucleus; their DNA is free in the cytoplasm, and they have no membrane-bound organelles.
真核细胞（植物和动物细胞）具有真正的细胞核，内含染色体和膜结合细胞器。原核细胞（细菌）没有细胞核；其 DNA 游离在细胞质中，也没有膜结合细胞器。
Prokaryotes: DNA in cytoplasm, no nucleus, smaller ribosomes, no mitochondria or chloroplasts, cell wall made of peptidoglycan (not cellulose).
原核生物：DNA 在细胞质中，无细胞核，核糖体较小，无线粒体和叶绿体，细胞壁由肽聚糖（而非纤维素）组成。
Eukaryotes: DNA in nucleus, membrane-bound organelles, larger ribosomes, may have mitochondria/chloroplasts.
真核生物：DNA 在细胞核中，有膜结合细胞器，核糖体较大，可能有线粒体/叶绿体。
10. Summary and Exam Tips | 总结与考试要点
wall, vacuole, and chloroplasts; organisation order is cells → tissues → organs → systems.
请记住这些高频考点：细胞膜具有选择透过性；线粒体通过有氧呼吸释放能量；核糖体制造蛋白质；叶绿体用于光合作用；植物细胞有细胞壁、液泡和叶绿体；组织层次顺序是细胞 → 组织 → 器官 → 系统。
In the exam, when asked to compare animal and plant cells, use a table with clear contrasting statements. When asked about specialised cells, always link the structural feature to its function to gain full marks.
考试中，当要求比较动物细胞和植物细胞时，请使用表格列出清晰的对比。当问到特化细胞时，一定要将结构特征与功能联系起来，才能获得满分。
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