📚 IGCSE CIE Biology: Cell Structure – Key Points | IGCSE CIE 生物：细胞结构 考点精讲
Understanding cell structure is fundamental to IGCSE CIE Biology. This guide breaks down the essential exam points on organelles, differences between plant and animal cells, prokaryotes, cell specialisation and microscopy, ensuring you can tackle both theory and practical questions with confidence.
理解细胞结构是IGCSE CIE生物学的基础。本指南详细解析细胞器、动植物细胞差异、原核生物、细胞特化以及显微镜使用等必考要点，帮助你自信应对理论和实验题。
1. Cell Theory and the Basis of Life | 细胞学说与生命基础
All living organisms are made up of cells. The cell is the smallest unit that can carry out all processes of life, and all cells arise only from pre-existing cells through division.
所有生物都由细胞构成。细胞是能够进行所有生命过程的最小单位，并且所有细胞只能通过分裂从已存在的细胞产生。
Viruses are not considered living because they lack a cellular structure, do not carry out metabolism outside a host, and can only reproduce inside living cells.
病毒不被视为生物，因为它们缺乏细胞结构，在宿主外不进行代谢，且只能在活细胞内繁殖。
A typical cell is measured in micrometres (µm). Knowledge of the cell theory underpins all topics in biology, from respiration to inheritance.
典型细胞以微米（µm）为单位。细胞学说是从呼吸作用到遗传等所有生物学主题的基础。
2. Animal Cell Structure | 动物细胞结构
A typical animal cell, such as a liver cell, is surrounded by a partially permeable cell membrane that controls the passage of substances into and out of the cell.
典型的动物细胞，如肝细胞，由一层选择透过性细胞膜包围，控制物质进出细胞。
The nucleus is a large organelle containing chromosomes made of DNA. It controls cell activities and is responsible for protein synthesis instructions and cell division.
细胞核是一个大型细胞器，含有由DNA组成的染色体。它控制细胞活动，负责蛋白质合成指令和细胞分裂。
Mitochondria are the sites of aerobic respiration, where glucose is broken down to release energy in the form of ATP. Cells with high energy demands, like muscle cells, contain many mitochondria.
线粒体是有氧呼吸的场所，葡萄糖在此分解并释放以ATP形式存在的能量。能量需求高的细胞，如肌肉细胞，含有大量线粒体。
Ribosomes are tiny organelles found free in the cytoplasm or attached to the rough endoplasmic reticulum. They synthesise proteins by linking amino acids together.
核糖体是微小的细胞器，游离于细胞质中或附着在粗糙内质网上。它们通过连接氨基酸来合成蛋白质。
The cytoplasm is a jelly-like substance where many metabolic reactions occur. It contains organelles, enzymes and dissolved nutrients.
细胞质是一种胶状物质，许多代谢反应在此进行。它包含细胞器、酶和溶解的营养物质。
3. Plant Cell Structure | 植物细胞结构
Plant cells share many organelles with animal cells but also possess three distinctive structures: a cellulose cell wall, a large permanent vacuole, and chloroplasts.
植物细胞与动物细胞共享许多细胞器，但也拥有三种特有结构：纤维素细胞壁、大型永久液泡和叶绿体。
The cell wall, made of cellulose, lies outside the cell membrane. It provides structural support, prevents bursting when the cell absorbs water, and is fully permeable.
细胞壁由纤维素构成，位于细胞膜外。它提供结构支撑，防止细胞吸水时破裂，并具有完全渗透性。
Chloroplasts contain the green pigment chlorophyll and are the sites of photosynthesis. They are found mainly in the palisade mesophyll cells of leaves and in stem cells of some plants.
叶绿体含有绿色色素叶绿素，是光合作用的地点。它们主要存在于叶子的栅栏组织细胞和一些植物的茎细胞中。
A large central vacuole contains cell sap, a solution of water, sugars and salts. It helps maintain turgor pressure, pushing the cytoplasm against the cell wall and keeping the plant rigid.
中央大液泡含有细胞液，即水、糖和盐的溶液。它有助于维持膨压，将细胞质推向细胞壁，使植物保持坚挺。
4. Functions of Organelles – Detailed Table | 细胞器功能详表
The table below consolidates the key organelles examined in IGCSE Biology, their functions and where they are found. Use it as a quick revision checklist.
下表汇总了IGCSE生物中考查的关键细胞器、它们的功能及存在部位。可将其作为快速复习清单。
| Organelle | Function | Found in |
|---|---|---|
| Cell membrane | Selective barrier; controls entry and exit | Animal, plant, bacteria |
| Nucleus | Contains genetic material; regulates activities | Animal, plant (not bacteria) |
| Cytoplasm | Site of metabolic reactions | Animal, plant, bacteria |
| Mitochondrion | Aerobic respiration; ATP production | Animal, plant |
| Ribosome | Protein synthesis | Animal, plant, bacteria |
| Chloroplast | Photosynthesis; traps light energy | Plant only |
| Cell wall | Support and shape; prevents bursting | Plant (cellulose), bacteria (peptidoglycan) |
| Permanent vacuole | Stores cell sap; maintains turgor | Plant |
| Plasmid | Small ring of DNA; carries additional genes | Bacteria only |
Notice that mitochondria and chloroplasts are membrane-bound organelles, absent in prokaryotes. Ribosomes are present in all cells but are smaller (70S) in bacteria.
请注意，线粒体和叶绿体是膜结合细胞器，原核生物中没有。核糖体存在于所有细胞中，但在细菌中较小（70S型）。
5. Comparison: Animal vs Plant Cells | 动物细胞与植物细胞比较
Exam questions often ask you to list the structural differences between a typical animal cell and a plant cell. The following pairs highlight the crucial contrasts.
试题常要求列出典型动物细胞与植物细胞的结构差异。以下要点突出了关键对比。
Plant cells have a rigid cell wall made of cellulose; animal cells lack a cell wall and have only a cell membrane.
植物细胞有由纤维素构成的坚硬细胞壁；动物细胞没有细胞壁，只有细胞膜。
Plant cells contain chloroplasts for photosynthesis; animal cells never have chloroplasts because they cannot make their own food.
植物细胞含有用于光合作用的叶绿体；动物细胞绝无叶绿体，因为它们无法自己制造食物。
Plant cells usually have a large, central permanent vacuole that fills much of the cell; animal cells have small, temporary vacuoles if any.
植物细胞通常有一个占细胞大部分体积的中央大液泡；动物细胞如果有液泡，也是小而临时的。
Both cell types have a nucleus, mitochondria and ribosomes, but plant cells often store excess glucose as starch grains, while animal cells store glycogen granules.
两种细胞都有细胞核、线粒体和核糖体，但植物细胞常以淀粉粒储存多余葡萄糖，而动物细胞储存糖原颗粒。
6. Prokaryotic Cells: Bacteria | 原核细胞：细菌
Bacteria are single-celled prokaryotes. They are much smaller than eukaryotic cells and have a much simpler structure without a true nucleus or membrane-bound organelles.
细菌是单细胞原核生物。它们比真核细胞小得多，结构简单得多，没有真正的细胞核或膜结合细胞器。
The genetic material in a bacterium is a single circular chromosome made of DNA, lying free in the cytoplasm in a region called the nucleoid. Additional small DNA rings, called plasmids, often carry genes for antibiotic resistance.
细菌中的遗传物质是单个环状DNA染色体，游离于细胞质中称为拟核的区域。额外的小DNA环，称为质粒，常携带抗生素抗性基因。
Bacterial cells have a cell wall made of peptidoglycan (different from plant cellulose), a cell membrane, cytoplasm, and 70S ribosomes. Some possess a flagellum for movement or a slime capsule for protection.
细菌细胞具有由肽聚糖构成的细胞壁（与植物纤维素不同）、细胞膜、细胞质和70S核糖体。有些细菌具有用于运动的鞭毛或用于保护的黏液荚膜。
In the exam, you must be able to label a diagram of a bacterial cell and compare its features with a plant or animal cell. Remember that bacteria never have mitochondria, chloroplasts or a nuclear membrane.
考试中，你必须能够标注细菌细胞图并比较其与动植物细胞的特征。请记住，细菌绝没有线粒体、叶绿体或核膜。
7. Cell Specialisation | 细胞特化
Multicellular organisms contain cells that are adapted to perform specific functions. The structure of each specialised cell is closely linked to its role. Here are the IGCSE favourites.
多细胞生物包含适应执行特定功能的细胞。每个特化细胞的结构与其作用密切相关。以下是IGCSE常考的特化细胞。
Red blood cells are biconcave discs with no nucleus and a flexible shape. They are packed with haemoglobin to carry oxygen, and their large surface area to volume ratio speeds up gas exchange.
红血球是双凹圆盘形，无核且形状灵活。它们充满血红蛋白以运输氧气，其巨大的表面积与体积比加速气体交换。
Nerve cells (neurones) have a long axon insulated by a myelin sheath and branched dendrites. This shape allows rapid transmission of electrical impulses over long distances.
神经细胞（神经元）具有由髓鞘绝缘的长轴突和分支树突。这种形状允许电脉冲远距离快速传递。
Sperm cells are streamlined with a tail (flagellum) for swimming. They contain many mitochondria in the mid-piece to provide ATP for movement and have an acrosome containing enzymes to penetrate the egg.
精子细胞呈流线型，具有用于游动的尾部（鞭毛）。中段含有大量线粒体以提供运动所需的ATP，并具有顶体，内含穿透卵子的酶。
Root hair cells are found near the tips of roots and have a long, thin extension that increases the surface area for absorption of water and mineral ions from the soil.
根毛细胞位于根尖附近，具有长而薄的突起，增加表面积以从土壤中吸收水分和矿物离子。
Palisade mesophyll cells are column-shaped and tightly packed in leaves. They contain abundant chloroplasts aligned near the cell surface to capture the maximum light for photosynthesis.
栅栏叶肉细胞呈柱状，在叶片中紧密排列。它们含有大量叶绿体，靠近细胞表面对齐，以捕获最多光线进行光合作用。
Ciliated epithelial cells line the trachea and bronchi. They possess tiny hair-like cilia that beat in a coordinated pattern to sweep mucus and trapped pathogens away from the lungs.
纤毛上皮细胞排列在气管和支气管内。它们具有微小的毛发状纤毛，以协调的方式摆动，将黏液和捕获的病原体扫出肺部。
8. Measuring Cells: Magnification and Size | 细胞测量：放大与尺寸
Microscopy calculations appear frequently in Paper 2 and Paper 4. You must be able to use the magnification formula and convert units confidently.
显微镜计算常出现在试卷二和试卷四中。你必须能够自信地使用放大公式并转换单位。
Magnification = Image size ÷ Actual size
Make sure image size and actual size are in the same units before calculating. The actual size is usually given in micrometres (µm) or millimetres (mm).
计算前确保图像大小和实际大小单位相同。实际大小通常以微米（µm）或毫米（mm）给出。
Unit conversions are crucial: 1 mm = 1000 µm; 1 µm = 1000 nm. To convert from mm to µm, multiply by 1000. To convert µm to mm, divide by 1000.
单位换算至关重要：1 mm = 1000 µm；1 µm = 1000 nm。从毫米转换到微米，乘以1000；微米到毫米，除以1000。
Example: A cell in a micrograph measures 50 mm across. The actual diameter is 0.05 mm. Magnification = 50 mm ÷ 0.05 mm = ×1000. In micrometres: actual size 0.05 mm = 50 µm; image size 50 mm = 50,000 µm; so magnification = 50,000 ÷ 50 = ×1000.
示例：显微照片中一个细胞的直径为50毫米。实际直径是0.05毫米。放大倍数 = 50 mm ÷ 0.05 mm = ×1000。以微米计：实际大小0.05 mm = 50 µm；图像大小50 mm = 50000 µm；因此放大倍数 = 50000 ÷ 50 = ×1000。
When measuring image size with a ruler, record in mm, then convert to the same unit as the actual size before division. Always show your working for full marks.
用直尺测量图像大小时，以毫米记录，然后将单位转换为与实际大小相同后再相除。始终展示解题过程以获得满分。
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