📚 IGCSE Biology: Cell Structure Key Points | IGCSE 生物：细胞结构 考点精讲
Welcome to this focused revision guide on cell structure for IGCSE Biology. We will explore the key concepts you need to master, from organelles and their functions to specialised cells and microscopy skills. Each section pairs an English explanation with its Chinese equivalent to support bilingual learners.
欢迎阅读这篇 IGCSE 生物细胞结构考点精讲。我们将深入探讨你需要掌握的核心概念，从细胞器及其功能到特化细胞和显微镜技能。每个部分都以英文解释与中文解释配对呈现，以支持双语学习者。
1. Introduction to Cell Structure | 细胞结构简介
All living organisms are made of cells, the basic structural and functional units of life. IGCSE Biology requires you to recognise the main features of animal, plant, bacterial and fungal cells, and to understand how their structures relate to their functions.
所有生物体都由细胞构成，细胞是生命的基本结构和功能单位。IGCSE 生物要求你识别动物、植物、细菌和真菌细胞的主要特征，并理解其结构如何与功能相适应。
The cell theory states that cells arise from pre-existing cells, all organisms are composed of one or more cells, and the cell is the smallest unit of life. You should be comfortable using a light microscope to observe and draw cells.
细胞学说指出，细胞来自已有细胞，所有生物都由一个或多个细胞组成，细胞是生命的最小单位。你应该能够熟练使用光学显微镜观察并绘制细胞图。
2. Animal Cells | 动物细胞
A typical animal cell, such as a human cheek cell, contains a cell membrane, cytoplasm, a nucleus, mitochondria and ribosomes. Under the light microscope, the nucleus is often the most visible organelle.
典型的动物细胞，如人的口腔上皮细胞，含有细胞膜、细胞质、细胞核、线粒体和核糖体。在光学显微镜下，细胞核通常是最容易看到的细胞器。
Animal cells lack a cell wall, a permanent vacuole and chloroplasts. Instead, they may have small temporary vacuoles and store carbohydrates as glycogen. The cell membrane controls the passage of substances into and out of the cell.
动物细胞没有细胞壁、永久液泡和叶绿体。相反，它们可能具有临时的小液泡，并以糖原的形式储存碳水化合物。细胞膜控制物质进出细胞。
The cytoplasm is a jelly-like substance where most chemical reactions occur. Ribosomes, which are too small to see with a light microscope, are the sites of protein synthesis.
细胞质是一种凝胶状物质，大多数化学反应在此进行。核糖体太小，无法用光学显微镜看到，是蛋白质合成的场所。
3. Plant Cells | 植物细胞
Plant cells share the same basic components as animal cells but possess three additional structures: a rigid cell wall made of cellulose, a large permanent vacuole filled with cell sap, and chloroplasts that carry out photosynthesis.
植物细胞与动物细胞有相同的基本结构，但另外具有三种结构：由纤维素构成的坚硬细胞壁、充满细胞液的大永久液泡，以及进行光合作用的叶绿体。
The cell wall provides structural support and prevents the cell from bursting when water enters by osmosis. The permanent vacuole stores water, ions and waste, and helps maintain turgor pressure inside the cell.
细胞壁提供结构支撑，并防止细胞在水分通过渗透进入时破裂。永久液泡储存水分、离子和废物，并有助于维持细胞内的膨压。
Chloroplasts contain the green pigment chlorophyll, which absorbs light energy for photosynthesis. Plant cells store carbohydrates as starch, often visible as grains inside chloroplasts or the cytoplasm.
叶绿体含有绿色色素叶绿素，吸收光能用于光合作用。植物细胞以淀粉的形式储存碳水化合物，通常在叶绿体或细胞质中可见淀粉粒。
4. Bacterial Cells | 细菌细胞
Bacteria are prokaryotes, meaning their genetic material is not enclosed in a nuclear membrane. The DNA forms a single circular chromosome and small rings of DNA called plasmids float freely in the cytoplasm.
细菌是原核生物，意味着它们的遗传物质没有被核膜包裹。DNA 形成一个单一的环状染色体，称为质粒的小环状 DNA 在细胞质中自由漂浮。
A bacterial cell has a cell wall (made of peptidoglycan, not cellulose), a cell membrane, cytoplasm, ribosomes, and sometimes a slime capsule for protection. Some bacteria possess flagella for movement.
细菌细胞具有细胞壁（由肽聚糖构成，而非纤维素）、细胞膜、细胞质、核糖体，有时还具有用于保护的荚膜。一些细菌拥有用于运动的鞭毛。
You must be able to label a bacterium and compare it with plant and animal cells. Note the absence of mitochondria and a nucleus; respiration occurs on the cell membrane instead.
你必须能够标记细菌并与动植物细胞进行比较。注意细菌无线粒体和细胞核；呼吸作用在细胞膜上进行。
5. Fungal Cells | 真菌细胞
Fungi, such as yeast and Mucor, have eukaryotic cells with a true nucleus. Their cell walls are made of chitin, not cellulose, and they store carbohydrates as glycogen, similar to animals.
真菌（例如酵母和毛霉）具有真核细胞，含有真正的细胞核。它们的细胞壁由几丁质构成，而不是纤维素，并且像动物一样以糖原的形式储存碳水化合物。
Yeast is a single-celled fungus often used in IGCSE questions. It has a cell wall, cell membrane, cytoplasm, nucleus, mitochondria and vacuoles. Yeast can reproduce by budding under a microscope.
酵母是一种常用于 IGCSE 试题的单细胞真菌。它具有细胞壁、细胞膜、细胞质、细胞核、线粒体和液泡。在显微镜下可观察到酵母通过出芽繁殖。
Multicellular fungi, such as Mucor, form thread-like hyphae. The hyphae may or may not have cross-walls (septa) and contain multiple nuclei. Saprophytic fungi secrete digestive enzymes onto their food.
多细胞真菌（如毛霉）形成丝状的菌丝。菌丝可能有或没有横壁（隔膜），并含有多个细胞核。腐生真菌将消化酶分泌到食物上。
6. Organelles and Their Functions | 细胞器及其功能
Memorising the function of each organelle is essential. Below is a summary table you can use for revision.
记住每个细胞器的功能至关重要。下面是一个可用于复习的总结表。
| Organelle | Function | 细胞器 | 功能 |
| Nucleus | Contains genetic material and controls cell activities | 细胞核 | 含有遗传物质，控制细胞活动 |
| Cell membrane | Selectively permeable barrier; controls entry and exit of substances | 细胞膜 | 选择性通透屏障；控制物质进出 |
| Mitochondria | Site of aerobic respiration; releases energy (ATP) | 线粒体 | 有氧呼吸场所；释放能量 (ATP) |
| Ribosomes | Protein synthesis | 核糖体 | 蛋白质合成 |
| Chloroplasts | Absorb light energy for photosynthesis to make glucose | 叶绿体 | 吸收光能进行光合作用制造葡萄糖 |
| Cell wall | Provides support, prevents bursting (cellulose in plants, chitin in fungi, peptidoglycan in bacteria) | 细胞壁 | 提供支撑，防止破裂 (植物纤维素，真菌几丁质，细菌肽聚糖) |
| Permanent vacuole | Stores cell sap (water, ions, wastes) and maintains turgor | 永久液泡 | 储存细胞液 (水、离子、废物)，维持膨压 |
| Plasmids | Small rings of DNA in bacteria carrying extra genes | 质粒 | 细菌中携带额外基因的小环状 DNA |
For IGCSE, you should be able to match organelles to their functions and explain why certain cells have more of a particular organelle (e.g. muscle cells have many mitochondria for energy).
对于 IGCSE，你应该能够将细胞器与其功能进行匹配，并解释为什么某些细胞含有较多的特定细胞器（例如肌肉细胞有许多线粒体以提供能量）。
7. Comparison of Cell Types | 细胞类型比较
Exam questions frequently ask you to compare animal, plant, fungal and bacterial cells. Use a table to note the presence or absence of key features.
试题经常要求你比较动物、植物、真菌和细菌细胞。使用一个表格来记录关键特征的有无。
| Feature | Animal | Plant | Fungus | Bacterium |
| Nucleus | ✓ | ✓ | ✓ | ✗ (free DNA) |
| Cell wall | ✗ | ✓ (cellulose) | ✓ (chitin) | ✓ (peptidoglycan) |
| Chloroplasts | ✗ | ✓ | ✗ | ✗ |
| Permanent vacuole | ✗ | ✓ | Sometimes | ✗ |
| Mitochondria | ✓ | ✓ | ✓ | ✗ |
| Plasmids | ✗ | ✗ | ✗ | Often present |
Understanding these differences helps you classify unknown cells from diagrams. Always check for a nucleus first: if absent, the cell is likely prokaryotic (bacterium).
理解这些差异有助于你根据图示对未知细胞进行分类。始终首先检查细胞核：如果不存在，该细胞很可能是原核生物（细菌）。
8. Specialised Cells | 特化细胞
In multicellular organisms, cells differentiate to perform particular functions. The structure of a specialised cell is closely linked to its job. You must know specific examples for IGCSE.
在多细胞生物中，细胞分化以执行特定的功能。特化细胞的结构与其工作密切相关。你必须了解 IGCSE 的具体例子。
Red blood cell (animal): Biconcave disc shape increases surface area for oxygen absorption; no nucleus, providing more space for haemoglobin.
红细胞 (动物): 双凹圆盘形状增加了吸收氧气的表面积；没有细胞核，为血红蛋白提供更多空间。
Nerve cell (animal): Long axon and branched dendrites enable transmission of electrical impulses over long distances.
神经细胞 (动物): 长轴突和分支状的树突使得电冲动能够长距离传递。
Sperm cell (animal): Acrosome contains enzymes to digest the egg membrane, and a flagellum (tail) allows it to swim.
精子细胞 (动物): 顶体含有消化卵膜的酶，鞭毛（尾巴）使其能够游动。
Root hair cell (plant): Long projection increases surface area for absorption of water and mineral ions from soil.
根毛细胞 (植物): 长突起增加了从土壤中吸收水分和矿物质离子的表面积。
Palisade mesophyll cell (plant): Packed with chloroplasts arranged near the top of the leaf to maximise light absorption for photosynthesis.
栅栏叶肉细胞 (植物): 含有大量叶绿体，排列在叶片上部，以最大限度吸收光能进行光合作用。
Ciliated epithelial cell (animal): Tiny hair-like cilia beat in a coordinated wave to move mucus and trapped particles.
纤毛上皮细胞 (动物): 微小的毛发状纤毛以协调的波状摆动，移动黏液和捕获的颗粒。
9. Microscopy and Magnification | 显微镜与放大率
A light microscope uses lenses to magnify small objects. You must be able to identify the eyepiece lens, objective lenses, stage, coarse and fine focus knobs, mirror or light source.
光学显微镜使用镜片放大微小物体。你必须能够识别目镜、物镜、载物台、粗/细准焦螺旋、反光镜或光源。
Total magnification is calculated by multiplying the magnification of the eyepiece lens by the magnification of the objective lens. For example, a ×10 eyepiece with a ×40 objective gives ×400 magnification.
总放大率通过目镜放大倍数乘以物镜放大倍数来计算。例如，×10 的目镜与 ×40 的物镜组合可得到 ×400 的放大率。
When drawing cells from microscope observations, always use a sharp pencil, add a clear title, label structures using straight ruled lines, and state the magnification. Do not shade or colour your diagrams.
当根据显微镜观察绘制细胞图时，始终使用锋利的铅笔，添加清晰的标题，用直尺画线标注结构，并注明放大倍数。不要在你的图上加阴影或上色。
10. Magnification Calculations | 放大率计算
IGCSE exams will test your ability to calculate magnification, actual size or image size using the formula:
IGCSE 考试会测试你使用以下公式计算放大率、实际大小或图像大小的能力：
Magnification (M) = Image size (I) / Actual size (A)
放大率 (M) = 图像大小 (I) / 实际大小 (A)
Remember to convert units so that image size and actual size are in the same unit before dividing. Common units: 1 mm = 1000 µm (micrometres); 1 µm = 1000 nm (nanometres).
记得在相除之前转换单位，使图像大小和实际大小单位一致。常见单位：1 毫米 = 1000 微米 (µm)；1 微米 = 1000 纳米 (nm)。
For example, if a cell measures 5 mm (5000 µm) under the microscope and its actual length is 50 µm, the magnification is 5000 ÷ 50 = ×100. Always include the multiplication sign (×) in your answer.
例如，如果一个细胞在显微镜下测量为 5 毫米（5000 微米），其实际长度为 50 微米，则放大率为 5000 ÷ 50 = ×100。在你的答案中始终包含乘号 (×)。
11. Levels of Organisation | 组织层次
Cells group together to form higher levels of organisation. You should know the hierarchy: cell → tissue → organ → organ system → organism.
细胞聚集在一起形成更高的组织层次。你应该知道这个层级：细胞 → 组织 → 器官 → 器官系统 → 生物体。
A tissue is a group of similar cells working together, such as muscle tissue or xylem tissue. An organ is made of several tissues, like the heart containing muscle, nerve and epithelial tissues. Organ systems are groups of organs, e.g. the digestive system.
组织是一组协同工作的相似细胞，例如肌肉组织或木质部组织。器官由几种组织构成，如心脏含有肌肉组织、神经组织和上皮组织。器官系统是器官的集合，如消化系统。
In plants, tissues include palisade mesophyll, spongy mesophyll, epidermis, xylem and phloem. The leaf is an organ, and the shoot system includes stems, leaves and flowers.
在植物中，组织包括栅栏叶肉、海绵叶肉、表皮、木质部和韧皮部。叶是器官，地上系统包括茎、叶和花。
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