📚 Cell Organelles: Key Points for IGCSE WJEC Biology | 细胞器考点精讲
Welcome to this focused revision guide on cell organelles for the IGCSE WJEC Biology specification. Understanding the structure and function of organelles is central to mastering cell biology. This article breaks down each key organelle, highlights differences between plant and animal cells, and offers exam-ready tips to boost your confidence.
欢迎阅读这篇针对 IGCSE WJEC 生物考试中细胞器考点的精讲指南。掌握细胞器的结构和功能是学好细胞生物学的基础。本文将逐一解析关键细胞器，对比动植物细胞的差异，并提供实用的考试技巧，帮助你自信应考。
1. What Are Organelles? | 什么是细胞器？
Organelles are specialised structures within a cell that perform specific functions, much like organs in a body. They are usually membrane-bound in eukaryotic cells, allowing compartmentalisation of different biochemical processes. In IGCSE WJEC, you need to identify organelles from diagrams and explain their roles.
细胞器是细胞内执行特定功能的特化结构，就像身体里的器官一样。在真核细胞中，细胞器通常由膜包裹，使得不同的生化过程能够分隔进行。在 WJEC IGCSE 考试中，你需要从图中识别细胞器并解释它们的功能。
2. Cell Membrane – The Gatekeeper | 细胞膜——守门者
The cell membrane is a thin, flexible layer that surrounds all cells. It is composed mainly of a phospholipid bilayer with protein molecules embedded in it. This structure is described as the fluid mosaic model. Its main function is to control the movement of substances in and out of the cell; it is selectively permeable. The membrane also contains receptor proteins for cell communication.
细胞膜是包裹所有细胞的一层薄而柔韧的结构。它主要由磷脂双分子层和镶嵌其中的蛋白质分子组成，这种结构被描述为流动镶嵌模型。它的主要功能是控制物质进出细胞，具有选择透过性。膜上还含有用于细胞通讯的受体蛋白。
3. Nucleus – The Control Centre | 细胞核——控制中心
The nucleus is the largest organelle in most eukaryotic cells. It is surrounded by a double membrane called the nuclear envelope, which contains nuclear pores that allow molecules like mRNA to pass through. Inside, the nucleus contains chromatin (DNA wound around histone proteins) and a nucleolus where ribosomes are made. The nucleus controls all cell activities by regulating gene expression.
细胞核是大多数真核细胞中最大的细胞器。它由双层膜包裹，称为核膜，核膜上有核孔，允许 mRNA 等分子通过。细胞核内部含有染色质（缠绕在组蛋白上的 DNA）以及一个核仁，核仁是核糖体的合成场所。细胞核通过调控基因表达来控制细胞的所有活动。
4. Cytoplasm and Cytosol – The Reaction Medium | 细胞质与胞质溶胶——反应介质
The cytoplasm refers to all the material inside the cell membrane excluding the nucleus. It consists of cytosol (a jelly-like fluid mostly of water, salts, and organic molecules) and the organelles suspended in it. Many metabolic reactions, including part of anaerobic respiration and protein synthesis, occur in the cytoplasm. The cytosol also helps transport materials around the cell.
细胞质是指细胞膜以内、细胞核以外的所有物质。它由胞质溶胶（一种主要由水、盐和有机分子组成的胶状液体）和悬浮其中的细胞器组成。许多代谢反应，包括无氧呼吸的部分反应和蛋白质合成，都在细胞质中进行。胞质溶胶还帮助在细胞内运输物质。
5. Mitochondria – The Powerhouses | 线粒体——能量工厂
Mitochondria are oval-shaped organelles with a double membrane. The inner membrane is highly folded into structures called cristae, which increase the surface area for aerobic respiration. Inside is a fluid matrix containing enzymes, ribosomes, and mitochondrial DNA. Mitochondria are the site of aerobic respiration, where glucose is broken down using oxygen to release energy in the form of ATP. Cells that require a lot of energy, such as muscle cells and sperm cells, contain many mitochondria.
线粒体是椭圆形的细胞器，具有双层膜。内膜向内折叠形成称为嵴的结构，这增加了有氧呼吸的表面积。内部是含有酶、核糖体和线粒体 DNA 的液态基质。线粒体是有氧呼吸的场所，在这里葡萄糖利用氧气被分解，释放能量并储存在 ATP 中。需要大量能量的细胞，如肌细胞和精子细胞，含有许多线粒体。
6. Ribosomes – Protein Factories | 核糖体——蛋白质工厂
Ribosomes are tiny organelles made of ribosomal RNA and protein. They are not membrane-bound and can be found free in the cytoplasm or attached to the rough endoplasmic reticulum. Ribosomes are the site of protein synthesis (translation), where amino acids are assembled into polypeptide chains according to the sequence of mRNA. In WJEC exams, you may be asked to identify ribosomes on diagrams of RER.
核糖体是由核糖体 RNA 和蛋白质组成的小型细胞器。它们没有膜包裹，可以游离在细胞质中，也可以附着在粗糙内质网上。核糖体是蛋白质合成（翻译）的场所，在这里氨基酸根据 mRNA 的序列组装成多肽链。在 WJEC 考试中，你可能需要从 RER 的示意图中识别出核糖体。
7. Endoplasmic Reticulum – The Transport Network | 内质网——运输网络
The endoplasmic reticulum (ER) is a network of membrane-bound sacs and tubules. It comes in two forms: rough ER (RER) and smooth ER (SER). RER is studded with ribosomes and is involved in folding, processing, and transporting proteins, especially those destined for secretion. SER lacks ribosomes and is involved in synthesising lipids and detoxifying certain chemicals. The ER connects to the nuclear envelope and the Golgi apparatus.
内质网（ER）是由膜构成的囊状和管状网络。它有两种类型：粗糙内质网（RER）和光滑内质网（SER）。RER 上附着着核糖体，参与蛋白质的折叠、加工和运输，特别是那些将要分泌到细胞外的蛋白质。SER 没有核糖体，参与脂质的合成以及某些化学物质的解毒。内质网与核膜和高尔基体相连。
8. Golgi Apparatus – Packaging and Distribution | 高尔基体——包装与分发
The Golgi apparatus is a stack of flattened, membrane-bound sacs. It receives proteins and lipids from the ER in vesicles, modifies them (e.g., adding carbohydrate groups to form glycoproteins), and packages them into new vesicles for transport to other parts of the cell or for secretion outside the cell via exocytosis. It is particularly prominent in secretory cells, such as those in glands.
高尔基体是一叠由膜构成的扁平囊状结构。它通过囊泡接收来自内质网的蛋白质和脂质，对其进行修饰（例如添加碳水化合物基团形成糖蛋白），并将它们包装到新的囊泡中，运送到细胞的其他部位，或通过胞吐作用分泌到细胞外部。高尔基体在分泌细胞中特别显著，比如腺体细胞。
9. Chloroplasts – Sites of Photosynthesis | 叶绿体——光合作用场所
Chloroplasts are large, oval organelles found only in plant cells and some algae. They have a double membrane and an internal system of flattened sacs called thylakoids, which are stacked into grana. The thylakoid membranes contain chlorophyll, the green pigment that absorbs light energy. The stroma is the fluid-filled space where the Calvin cycle occurs. Overall equation for photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Chloroplasts are vital for producing glucose and oxygen.
叶绿体是仅存在于植物细胞和一些藻类中的大型椭圆形细胞器。它们具有双层膜，以及内部扁平的囊状结构——类囊体，类囊体垛叠形成基粒。类囊体膜上含有叶绿素，这种绿色色素能吸收光能。叶绿体基质是进行卡尔文循环的液态空间。光合作用的总反应式为：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。叶绿体对于生产葡萄糖和氧气至关重要。
10. Permanent Vacuole and Cell Wall – Plant Cell Extras | 永久液泡与细胞壁——植物细胞特有结构
Plant cells usually have a large, central permanent vacuole filled with cell sap, a solution of water, sugars, and salts. The vacuole pushes the cytoplasm against the cell wall, maintaining turgor pressure and helping the plant stay upright. The cell wall is an outer rigid layer made of cellulose fibres. It provides structural support, prevents bursting in hypotonic environments, and is fully permeable to water and dissolved substances. Fungal cell walls are made of chitin, not cellulose, but this is beyond the core WJEC plant cell requirement.
植物细胞通常有一个大的中央永久液泡，内部充满细胞液，这是一种含有水、糖类和盐类的溶液。液泡将细胞质挤向细胞壁，维持膨压，帮助植物保持直立。细胞壁是位于细胞膜外的刚性外层，由纤维素纤维构成。它提供结构支撑，防止细胞在低渗环境中胀破，并且对水及溶解物质是全透性的。真菌细胞壁由几丁质构成，而非纤维素，不过这超出了 WJEC 核心植物细胞的要求。
11. Comparing Plant and Animal Cells | 动植物细胞比较
The ability to compare plant and animal cells is a frequent WJEC exam skill. Use the table below to remember the key differences.
比较动植物细胞是 WJEC 考试中常考的技能。利用下表记住关键区别。
| Feature / 特征 | Animal Cell / 动物细胞 | Plant Cell / 植物细胞 |
|---|---|---|
| Cell wall / 细胞壁 | Absent / 无 | Present, made of cellulose / 有，由纤维素构成 |
| Chloroplasts / 叶绿体 | Absent / 无 | Present in green parts / 存在于绿色部分 |
| Permanent vacuole / 永久液泡 | Small, temporary vacuoles / 小且临时的液泡 | Large, central permanent vacuole / 大型中央永久液泡 |
| Shape / 形状 | Irregular / 不规则 | Fixed, fairly regular / 固定，较规则 |
| Food storage / 食物储存 | Glycogen granules / 糖原颗粒 | Starch grains / 淀粉粒 |
Both cell types contain a nucleus, cell membrane, mitochondria, ribosomes, ER, and Golgi apparatus. For WJEC, ensure you can label these on diagrams and describe the function of each organelle, explaining why plant cells have extra structures.
两种细胞都含有细胞核、细胞膜、线粒体、核糖体、内质网和高尔基体。在 WJEC 考试中，确保你能在图中标注这些结构，描述每种细胞器的功能，并解释植物细胞为何拥有额外的结构。
12. Common WJEC Exam Questions and Tips | WJEC 常见题型与技巧
Typical exam questions ask you to ‘identify the organelles labelled A, B, and C’ or to ‘explain how the structure of an organelle is adapted to its function’. When describing adaptations, always link the feature directly to the function. For example, the cristae of mitochondria increase surface area for more respiratory enzymes, allowing a higher rate of ATP production. Do not just name the part – explain why it matters. Diagrams are often electron micrographs or simple line drawings; practise recognising organelles by shape and location. Another common question asks for the differences between plant and animal cells; memorising the comparison table above will earn full marks. Finally, remember that ‘cell wall is freely permeable’ contrasts with the ‘selectively permeable cell membrane’, a frequent misconception.
典型的考题会要求你 ‘识别图中标记为 A、B、C 的细胞器’，或 ‘解释某个细胞器的结构如何适应其功能’。在描述适应性时，始终将特征与功能直接联系起来。例如，线粒体的嵴增加了表面积，以容纳更多的呼吸酶，从而提高了 ATP 的产量。不要仅仅说出结构的名称——要解释其重要性。考试图示通常是电子显微镜照片或简易线条图；练习根据形状和位置识别细胞器。另一个常见问题是比较动植物细胞的区别；熟记上面的对比表就能拿到满分。最后，记住 ‘细胞壁是全透性的’ 与 ‘细胞膜是选择透过性的’ 不同，这是一个常见的误解。
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