📚 IGCSE Biology Edexcel: Cell Structure | 细胞结构
Cells are the basic units of life. In the Edexcel IGCSE Biology specification, you need to know the structure and function of key organelles in animal and plant cells, as well as the differences between prokaryotic and eukaryotic cells. This article breaks down everything you need for your exam.
细胞是生命的基本单位。在 Edexcel IGCSE 生物考纲中，你需要掌握动物细胞和植物细胞中关键细胞器的结构与功能，以及原核细胞与真核细胞之间的区别。这篇文章将为你梳理考试所需的全部要点。
1. Common Features of Animal and Plant Cells | 动物细胞与植物细胞的共同结构
Both animal and plant cells are eukaryotic, meaning they have a true nucleus and membrane-bound organelles. The common structures you must label and describe include the cell membrane, cytoplasm, nucleus, mitochondria, and ribosomes.
动物细胞和植物细胞都属于真核细胞，意味着它们具有真正的细胞核和膜结合细胞器。你必须能够标注并描述的共同结构包括：细胞膜、细胞质、细胞核、线粒体和核糖体。
- Cell membrane – controls what enters and leaves the cell; partially permeable.
- Cytoplasm – jelly-like fluid where most chemical reactions occur; contains enzymes and organelles.
- Nucleus – contains DNA; controls the cell’s activities and protein synthesis.
- Mitochondria – site of aerobic respiration; releases energy from glucose.
- Ribosomes – site of protein synthesis.
细胞膜 – 控制物质进出细胞；具有选择透过性。
细胞质 – 胶状液体，大多数化学反应在此发生；含有酶和细胞器。
细胞核 – 含有 DNA；控制细胞活动及蛋白质合成。
线粒体 – 有氧呼吸的场所；从葡萄糖中释放能量。
核糖体 – 蛋白质合成的场所。
2. Additional Structures in Plant Cells | 植物细胞特有的结构
Plant cells have three additional structures not found in animal cells: a rigid cell wall made of cellulose, permanent vacuoles containing cell sap, and chloroplasts containing chlorophyll.
植物细胞具有三种动物细胞所没有的结构：由纤维素构成的坚硬细胞壁、含有细胞液的永久液泡，以及含有叶绿素的叶绿体。
- Cell wall – made of cellulose; provides strength and structural support.
- Vacuole – large, permanent; contains cell sap; helps maintain turgor pressure.
- Chloroplasts – contain chlorophyll; site of photosynthesis.
细胞壁 – 由纤维素构成；提供强度与结构支撑。
液泡 – 大而永久；含有细胞液；有助于维持膨压。
叶绿体 – 含有叶绿素；光合作用的场所。
3. Functions of Each Organelle in Detail | 各细胞器功能详解
You need to be able to match each organelle with its function in exam questions. Let’s go through them carefully.
在考试中，你需要能够将每个细胞器与其功能对应。让我们仔细逐一学习。
| Organelle 细胞器 | Function 功能 |
|---|---|
| Nucleus 细胞核 | Contains genetic material (DNA) and controls cell activities 含有遗传物质（DNA），控制细胞活动 |
| Cytoplasm 细胞质 | Site of many chemical reactions involving enzymes 许多酶促化学反应的场所 |
| Cell membrane 细胞膜 | Controls movement of substances in and out of cell 控制物质进出细胞 |
| Mitochondria 线粒体 | Aerobic respiration releases energy 有氧呼吸释放能量 |
| Ribosomes 核糖体 | Protein synthesis 蛋白质合成 |
| Cell wall 细胞壁 | Provides support and prevents bursting (plant cells) 提供支撑并防止胀破（植物细胞） |
| Vacuole 液泡 | Maintains turgidity; stores cell sap 维持膨压；储存细胞液 |
| Chloroplast 叶绿体 | Photosynthesis using light energy 利用光能进行光合作用 |
4. Prokaryotic vs Eukaryotic Cells | 原核细胞与真核细胞
Bacteria are prokaryotic cells. They do not have a nucleus or membrane-bound organelles. Their DNA is found free in the cytoplasm, usually as a circular loop. They may also have small rings of DNA called plasmids.
细菌属于原核细胞。它们没有细胞核或膜结合细胞器。它们的 DNA 游离在细胞质中，通常是环状。它们还可能含有称为质粒的小型环状 DNA。
| Feature 特征 | Prokaryotic (Bacteria) 原核（细菌） | Eukaryotic (Animal/Plant) 真核（动物/植物） |
|---|---|---|
| Nucleus 细胞核 | Absent 无 | Present 有 |
| Membrane-bound organelles 膜结合细胞器 | Absent 无 | Present 有 |
| DNA location DNA位置 | Free in cytoplasm (circular) 游离于细胞质（环状） | Inside nucleus (linear) 细胞核内（线状） |
| Ribosomes 核糖体 | Present (small) 有（小） | Present (larger) 有（较大） |
| Examples 例子 | Bacteria 细菌 | Animals, plants, fungi 动物、植物、真菌 |
5. Specialised Cells | 特化细胞
In exams, you may be asked how a cell’s structure is adapted to its function. Here are the key specialised cells you need to know.
考试中可能会问你细胞的结构如何适应其功能。以下是需要掌握的关键特化细胞。
Red blood cells – biconcave disc shape increases surface area for oxygen uptake; contain haemoglobin; no nucleus for more space.
红细胞 – 双凹圆盘状增加了吸收氧气的表面积；含有血红蛋白；无细胞核以腾出更多空间。
Root hair cells – long hair-like extension increases surface area for water and mineral absorption; large permanent vacuole speeds osmosis.
根毛细胞 – 细长的毛状突起扩大了吸收水分和矿物质的表面积；大液泡加速渗透作用。
Palisade mesophyll cells – packed with chloroplasts near the top of the leaf to capture maximum light for photosynthesis.
栅栏组织细胞 – 靠近叶片上表面布满叶绿体，以最大限度捕捉光能进行光合作用。
Sperm cells – flagellum for swimming, mitochondria for energy, acrosome enzymes to penetrate egg.
精子细胞 – 鞭毛用于游动，线粒体提供能量，顶体酶用于穿透卵细胞。
6. Cell Organisation: From Cell to Organism | 细胞组织：从细胞到生物体
Cells are organised into tissues, organs, and organ systems in multicellular organisms. This hierarchy is a common exam topic.
在多细胞生物中，细胞组织成组织、器官和器官系统。这一层级关系是常见考点。
Cell → Tissue → Organ → Organ System → Organism
细胞 → 组织 → 器官 → 器官系统 → 生物体
- Tissue: group of cells with similar structure and function. For example, muscle tissue or xylem tissue. 组织：由结构和功能相似的细胞组成。例如肌肉组织或木质部组织。
- Organ: group of tissues working together. For example, the stomach contains muscle, nerve, and epithelial tissue. 器官：多种组织协同工作。例如胃包含肌肉、神经和上皮组织。
- Organ system: several organs performing a major function. For example, the digestive system. 器官系统：多个器官完成一项主要功能。例如消化系统。
7. Calculating Magnification | 计算放大倍数
You may be asked to calculate magnification using the formula: magnification = image size / actual size. Always use the same units when calculating.
你可能会被要求使用公式计算放大倍数：放大倍数 = 图像大小 / 实际大小。计算时务必使用相同的单位。
Magnification = Image size ÷ Actual size
放大倍数 = 图像大小 ÷ 实际大小
Example: A cell is 2 mm in a diagram, but its actual length is 0.02 mm. Magnification = 2 ÷ 0.02 = ×100.
例如：图中细胞大小为 2 mm，实际长度为 0.02 mm。放大倍数 = 2 ÷ 0.02 = ×100。
8. Diffusion, Osmosis, and Active Transport | 扩散、渗透与主动转运
Movement of substances across cell membranes is essential. You must compare the three processes clearly.
物质跨细胞膜的运动至关重要。你必须清楚比较这三种过程。
| Process 过程 | Movement direction 运动方向 | Energy 能量 | Example 例子 |
|---|---|---|---|
| Diffusion 扩散 | High → low concentration 高浓度 → 低浓度 | None 不需要 | Oxygen into cells 氧气进入细胞 |
| Osmosis 渗透 | High water potential → low water potential 高水势 → 低水势 | None 不需要 | Water into root hair 水分进入根毛 |
| Active transport 主动转运 | Low → high concentration (against gradient) 低浓度 → 高浓度（逆梯度） | Required (ATP) 需要（ATP） | Mineral ions into root hairs 矿物质离子进入根毛 |
9. Osmosis in Plant and Animal Cells | 渗透在植物与动物细胞中的影响
When placed in different solutions, cells behave predictably. You must know the terms hypotonic, hypertonic, and isotonic.
将细胞置于不同溶液中时，其表现可预测。你必须掌握低渗、高渗和等渗这三个术语。
In a hypotonic solution (high water potential outside), water enters animal cells, causing them to swell and burst (lysis). Plant cells become turgid but do not burst due to the cell wall.
在低渗溶液（外部水势高）中，水分进入动物细胞，使其膨胀并破裂（溶胞）。植物细胞变得膨大，但因细胞壁的存在不会破裂。
In a hypertonic solution (low water potential outside), water leaves animal cells, causing them to shrink (crenation). Plant cells become plasmolysed as the membrane pulls away from the cell wall.
在高渗溶液（外部水势低）中，水分离开动物细胞，使其缩小（皱缩）。植物细胞发生质壁分离，细胞膜与细胞壁分离。
In an isotonic solution, there is no net movement of water.
在等渗溶液中，水分没有净运动。
10. Exam Tips and Common Mistakes | 考试技巧与常见错误
Here are some quick tips to avoid losing marks in your IGCSE Biology exam.
以下是一些快速建议，帮助你在 IGCSE 生物考试中避免丢分。
- Always state the organelle name and a specific function – “nucleus controls the cell” is not enough; write “contains DNA and controls protein synthesis”.
- Always include units when calculating magnification.
- Do not confuse osmosis with diffusion: osmosis is specifically about water movement through a partially permeable membrane.
- For specialised cells, link the adaptation to the function explicitly, e.g., “biconcave shape increases surface area for faster oxygen diffusion”.
务必写出细胞器名称和具体功能 – 只写“细胞核控制细胞”不够；应写“含有 DNA 并控制蛋白质合成”。
计算放大倍数时务必带上单位。
不要混淆渗透与扩散：渗透特指水分子通过半透膜的运动。
对于特化细胞，要明确将结构与功能联系起来，例如“双凹形状增大了表面积，从而加快氧气扩散”。
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