📚 IGCSE CIE Biology: Organelles – Exam Essentials | IGCSE CIE 生物：细胞器 考点精讲
Understanding organelles is at the heart of IGCSE CIE Biology. You must be able to identify the main organelles in animal, plant and bacterial cells, explain their functions, and compare cell types. This exam-focused guide covers all the essential points you need for the syllabus, with clear explanations, comparisons and typical exam questions in mind.
理解细胞器是IGCSE CIE 生物的核心。你必须能够识别动物、植物和细菌细胞中的主要细胞器，解释其功能，并比较细胞类型。这份考点精讲指南涵盖了大纲所需的所有要点，包括清晰的解释、比较和常见考题思路。
1. Cell as the Basic Unit of Life | 细胞——生命的基本单位
All living organisms are made of cells. A cell is the smallest unit that can carry out life processes. Organelles are specialised structures within the cell that perform specific jobs.
所有生物都由细胞构成。细胞是能执行生命过程的最小单位。细胞器是细胞内部执行特定功能的特化结构。
The IGCSE syllabus requires you to recognise organelles from diagrams and electron micrographs. You also need to relate their structure to function.
IGCSE 大纲要求你从示意图和电子显微照片中识别细胞器，并能够将结构与功能联系起来。
2. Cell Membrane: Controlling Entry and Exit | 细胞膜：控制物质进出
The cell membrane is a partially permeable barrier that surrounds all cells. It is composed of a phospholipid bilayer with embedded proteins.
细胞膜是包围所有细胞的一种选择透过性屏障，由磷脂双分子层和嵌入其中的蛋白质组成。
Its main function is to control the movement of substances into and out of the cell. It allows small molecules like water, oxygen and carbon dioxide to pass freely, but restricts larger or charged molecules.
它的主要功能是控制物质进出细胞。它允许小分子如水和 O₂、CO₂ 自由通过，但限制较大或带电荷的分子。
Exam tip: Be able to explain the term ‘partially permeable’ and give examples of substances that can cross by diffusion or osmosis.
考试提示：能够解释“选择透过性”这个术语，并列举可以通过扩散或渗透穿过细胞膜的物质实例。
3. Nucleus: Genetic Material Storage | 细胞核：遗传物质的贮存
The nucleus is the control centre of the cell. It is surrounded by a double membrane called the nuclear envelope, which contains pores.
细胞核是细胞的控制中心。它被叫做核被膜的双层膜包围，膜上有核孔。
Inside the nucleus, DNA is organised into chromosomes. The nucleus controls cell activities by regulating protein synthesis through the transcription of genes into mRNA.
细胞核内，DNA 组织成染色体。细胞核通过调控基因转录为 mRNA 来调节蛋白质合成，从而控制细胞活动。
Not all cells have a nucleus. Red blood cells in mammals lose their nucleus during maturation, and bacterial cells lack a true nucleus (they have a nucleoid region instead).
并非所有细胞都有细胞核。哺乳动物的红细胞在成熟过程中会失去细胞核，而细菌细胞没有真正的细胞核（它们有拟核区域）。
4. Cytoplasm: Site of Metabolic Reactions | 细胞质：代谢反应的场所
Cytoplasm is the jelly-like substance that fills the cell, consisting mainly of water and dissolved solutes. It contains organelles and is the site of many chemical reactions.
细胞质是填充细胞的胶状物质，主要成分是水和溶解的溶质。它包含细胞器，是许多化学反应的场所。
In both animal and plant cells, anaerobic respiration (glycolysis) occurs in the cytoplasm. Enzyme-controlled reactions, such as those of protein synthesis, also take place here before ribosomes become involved.
在动物和植物细胞中，无氧呼吸（糖酵解）发生在细胞质中。酶控制的反应，比如蛋白质合成的前期步骤，也同样在此发生。
5. Mitochondria: Site of Aerobic Respiration | 线粒体：有氧呼吸的场所
Mitochondria are the ‘powerhouses’ of the cell. They have a double membrane; the inner membrane is folded into cristae to increase surface area for reactions.
线粒体是细胞的“能量工厂”。它们有双层膜；内膜折叠成嵴，以增加反应的表面积。
Aerobic respiration takes place in mitochondria, producing ATP. The overall equation is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy).
有氧呼吸在线粒体中进行，产生 ATP。总反应方程式为：C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O（+ 能量）。
Cells with high energy demands, such as muscle cells and sperm cells, contain large numbers of mitochondria. Rigorous exam questions might ask you to link this to cell function.
需要大量能量的细胞（如肌肉细胞和精子细胞）含有大量的线粒体。严格的考试题目可能要求你将这一点与细胞功能联系起来。
6. Ribosomes: Protein Synthesis | 核糖体：蛋白质合成
Ribosomes are tiny organelles made of ribosomal RNA and proteins. They can be found free in the cytoplasm or attached to the rough endoplasmic reticulum.
核糖体是由核糖体 RNA 和蛋白质组成的微小细胞器。它们可以游离在细胞质中，或附着在粗面内质网上。
Their sole function is to synthesise proteins by translating the genetic code carried by mRNA into a polypeptide chain. Ribosomes are present in all types of cells, including bacteria.
它们唯一的功能是通过将 mRNA 携带的遗传密码翻译成多肽链来合成蛋白质。所有类型的细胞中都存在核糖体，包括细菌。
7. Chloroplasts: Photosynthesis (Plants Only) | 叶绿体：光合作用（仅植物）
Chloroplasts are found in plant cells and some algae. They contain the green pigment chlorophyll, which absorbs light energy for photosynthesis.
叶绿体存在于植物细胞和一些藻类中。它们含有绿色色素叶绿素，吸收光能用于光合作用。
Photosynthesis equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Chloroplasts have a double membrane and internal stacks of thylakoids (grana) where the light-dependent reactions occur.
光合作用方程式：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂。叶绿体具有双层膜，内部有类囊体堆叠（基粒），光反应在此发生。
Key point: Chloroplasts are never present in animal or fungal cells. In exam diagrams, you may be asked to label them and explain why a cell in a leaf contains many chloroplasts.
关键点：动物细胞或真菌细胞中从不含有叶绿体。考试图中可能要求你标出它们，并解释为什么叶片细胞含有大量叶绿体。
8. Cell Wall: Structural Support | 细胞壁：结构支持
The cell wall is a rigid layer located outside the cell membrane. In plants, it is made of cellulose; in fungi, it is made of chitin; and in bacteria, it is made of peptidoglycan.
细胞壁是位于细胞膜外的坚硬层。植物细胞壁由纤维素构成；真菌细胞壁由几丁质构成；细菌细胞壁则由肽聚糖构成。
It provides structural support, prevents the cell from bursting when water enters by osmosis, and gives the cell a fixed shape. Animal cells do not have a cell wall.
它提供结构支撑，防止细胞在渗透吸水时胀破，并使细胞具有固定形状。动物细胞没有细胞壁。
9. Vacuole: Support and Storage | 液泡：支持与储存
Plant cells typically have a large, permanent central vacuole filled with cell sap (a solution of water, sugars, salts and pigments). The vacuole is surrounded by a membrane called the tonoplast.
植物细胞通常有一个大的中央液泡，充满细胞液（水、糖、盐和色素溶液）。液泡被叫做液泡膜的膜包围。
The vacuole helps maintain turgor pressure against the cell wall, supporting the plant structure. It also stores nutrients and waste products. Animal cells have small, temporary vacuoles, if any.
液泡有助于维持胞壁压力，支持植物结构。它也储存营养物质和废物。动物细胞如果有液泡，也是小而暂时的。
10. Comparing Animal and Plant Cells | 比较动物细胞与植物细胞
It is vital to know the similarities and differences between animal and plant cells. Both have a cell membrane, cytoplasm, nucleus, mitochondria and ribosomes. However, only plant cells have a cellulose cell wall, a large permanent vacuole and chloroplasts.
了解动物细胞和植物细胞的异同至关重要。两者都有细胞膜、细胞质、细胞核、线粒体和核糖体。但是，只有植物细胞具有纤维素细胞壁、大型中央液泡和叶绿体。
The table below summarises the key differences between a general animal cell and a plant cell.
下表总结了一般动物细胞与植物细胞之间的关键区别。
| Organelle / Feature | Animal Cell | Plant Cell |
|---|---|---|
| Cell membrane | Present | Present |
| Nucleus | Present | Present |
| Cytoplasm | Present | Present |
| Mitochondria | Present | Present |
| Ribosomes | Present | Present |
| Cell wall | Absent | Present (cellulose) |
| Chloroplast
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