📚 IGCSE AQA Biology: Cell Structure Key Points | IGCSE AQA 生物：细胞结构 考点精讲
Understanding cell structure is fundamental to IGCSE AQA Biology. This article covers the essential knowledge about cell types, organelles, and microscopy, pairing each concept in English and Chinese for clear bilingual revision. All key points are aligned with the AQA specification, making it a perfect resource for exam preparation.
理解细胞结构是 IGCSE AQA 生物学的基础。本文涵盖细胞类型、细胞器以及显微镜操作等核心知识，每个概念均以英中双语配对呈现，方便同学们清晰复习。所有考点紧密贴合 AQA 考纲，是备考的理想资料。
1. Cell Theory and Cell Types | 细胞学说与细胞类型
All living organisms are made of cells. The cell is the basic structural and functional unit of life. Cells arise from pre-existing cells by division. There are two main categories: prokaryotic cells (e.g. bacteria) which lack a nucleus, and eukaryotic cells (e.g. animal and plant cells) which have a distinct nucleus enclosed by a membrane.
所有生物体均由细胞构成。细胞是生命的基本结构和功能单位。细胞通过分裂产生于已有的细胞。细胞主要分为两类：原核细胞（如细菌）没有细胞核，真核细胞（如动物和植物细胞）具有由膜包被的完整细胞核。
Prokaryotic cells are generally much smaller and simpler. Their genetic material is a single loop of DNA free in the cytoplasm, and they may contain small rings of DNA called plasmids. Eukaryotic cells contain membrane-bound organelles, including mitochondria, chloroplasts, and the nucleus itself.
原核细胞通常更小、更简单。它们的遗传物质是游离在细胞质中的单链环状DNA，此外还可能含有被称为质粒的小型DNA环。真核细胞包含有膜细胞器，如线粒体、叶绿体以及细胞核本身。
2. Animal Cells: Key Organelles | 动物细胞：关键细胞器
A typical animal cell contains a cell membrane, cytoplasm, nucleus, mitochondria, and ribosomes. The cell membrane controls the entry and exit of substances. The cytoplasm is a jelly-like substance where most chemical reactions occur, supported by the cytoskeleton.
典型的动物细胞包含细胞膜、细胞质、细胞核、线粒体和核糖体。细胞膜控制物质的进出。细胞质是胶状物质，大多数化学反应在此进行，并由细胞骨架提供支撑。
The nucleus contains the genetic material (DNA) and controls the cell’s activities. Mitochondria are the sites of aerobic respiration, releasing energy in the form of ATP. Ribosomes are tiny structures where proteins are synthesised. Under the light microscope, ribosomes are not visible, but mitochondria can sometimes be seen as small rod-shaped organelles.
细胞核含有遗传物质（DNA），控制细胞活动。线粒体是有氧呼吸的场所，以ATP形式释放能量。核糖体是合成蛋白质的微小结构。在光学显微镜下，核糖体不可见，但线粒体有时可呈现为杆状小体。
3. Plant Cells: Unique Features | 植物细胞：独特结构
In addition to the organelles found in animal cells, plant cells possess a rigid cell wall made of cellulose, a large permanent vacuole filled with cell sap, and chloroplasts which contain chlorophyll for photosynthesis. These features allow plants to carry out distinctive functions.
除了动物细胞所含的细胞器外，植物细胞还拥有由纤维素构成的坚硬细胞壁、充满细胞液的大液泡以及含有叶绿体（内含叶绿素进行光合作用）。这些结构使植物能够执行独特的功能。
The cell wall provides structural support and prevents the cell from bursting when turgid. The permanent vacuole maintains cell shape and stores water, ions, and waste products. Chloroplasts absorb light energy to convert carbon dioxide and water into glucose, using the green pigment chlorophyll.
细胞壁提供结构支撑，并防止细胞在吸水饱满时胀破。大液泡维持细胞形状，储存水分、离子和废物。叶绿体利用绿色色素叶绿素吸收光能，将二氧化碳和水转化为葡萄糖。
4. Cell Membrane and Transport | 细胞膜与物质运输
All cells are surrounded by a cell membrane composed of a phospholipid bilayer with embedded proteins. This membrane is selectively permeable, meaning it allows some molecules to pass through but not others. Small molecules like oxygen, carbon dioxide, and water can diffuse directly through the membrane.
所有细胞都被细胞膜包裹，细胞膜由磷脂双分子层与嵌入的蛋白质构成。这层膜具有选择透过性，即允许某些分子通过而限制其他分子。氧气、二氧化碳和水等小分子可直接通过膜扩散。
Transport processes include diffusion (net movement of particles from high to low concentration), osmosis (diffusion of water through a selectively permeable membrane from a dilute to a more concentrated solution), and active transport (movement against the concentration gradient using energy from respiration). The cell membrane also contains carrier proteins that facilitate active transport and facilitated diffusion.
运输过程包括扩散（粒子从高浓度区域向低浓度区域的净移动）、渗透（水通过选择透过性膜从稀溶液向浓溶液的扩散）和主动运输（利用呼吸作用提供的能量逆着浓度梯度移动）。细胞膜还含有载体蛋白，协助主动运输和协助扩散。
5. Nucleus and DNA | 细胞核与DNA
The nucleus is the control centre of the cell. It contains deoxyribonucleic acid (DNA), organized into structures called chromosomes when the cell is about to divide. DNA carries the genetic instructions used in growth, development, and reproduction. In a non-dividing cell, DNA exists as a network of chromatin.
细胞核是细胞的控制中心。它含有脱氧核糖核酸（DNA），在细胞即将分裂时，DNA 组织成称为染色体的结构。DNA 携带着用于生长、发育和繁殖的遗传指令。在不分裂的细胞中，DNA 以染色质网络的形式存在。
The nucleus is surrounded by a nuclear envelope with pores that allow molecules like messenger RNA (mRNA) to exit after transcription. Inside the nucleus, a dense region called the nucleolus produces ribosomal RNA (rRNA) and assembles ribosome subunits. During the cell cycle, DNA replication occurs in the nucleus, ensuring genetic continuity.
细胞核由带核孔的核膜包围，允许信使RNA（mRNA）等分子在转录后离开。细胞核内部有一个致密区域——核仁，负责产生核糖体RNA（rRNA）并组装核糖体亚基。在细胞周期中，DNA 复制在细胞核内进行，确保遗传的连续性。
6. Mitochondria: Aerobic Respiration | 线粒体：有氧呼吸
Mitochondria are often referred to as the powerhouses of the cell because they perform aerobic respiration, a process that converts glucose and oxygen into ATP (adenosine triphosphate), releasing carbon dioxide and water as by-products. The word equation is: glucose + oxygen → carbon dioxide + water (+ energy).
线粒体常被称为细胞的能量工厂，因为它们进行有氧呼吸，该过程将葡萄糖和氧气转化为ATP（三磷酸腺苷），并释放二氧化碳和水作为副产物。文字方程式为：葡萄糖 + 氧气 → 二氧化碳 + 水（+ 能量）。
Mitochondria have a double membrane. The inner membrane is highly folded into cristae, which increase the surface area for the enzymes involved in the electron transport chain. The matrix inside contains mitochondrial DNA and ribosomes, which allow mitochondria to produce some of their own proteins and replicate independently of the cell cycle.
线粒体有两层膜。内膜向内折叠形成嵴，增大了参与电子传递链的酶所需的表面积。内部的基质含有线粒体DNA和核糖体，这使得线粒体能够合成自身部分蛋白质，并独立于细胞周期进行复制。
7. Ribosomes and Protein Synthesis | 核糖体与蛋白质合成
Ribosomes are the sites of protein synthesis (translation) in both prokaryotic and eukaryotic cells. They are composed of ribosomal RNA and proteins, and consist of two subunits. Ribosomes can be free in the cytoplasm or attached to the rough endoplasmic reticulum (RER).
核糖体是原核和真核细胞中蛋白质合成（翻译）的场所。它们由核糖体RNA和蛋白质组成，包含大小两个亚基。核糖体可以游离在细胞质中，也可以附着在粗面内质网（RER）上。
During protein synthesis, messenger RNA (mRNA) brings the genetic code from the nucleus to the ribosome. Transfer RNA (tRNA) then carries specific amino acids to the ribosome, where they are joined in the correct sequence to form a polypeptide chain. Many ribosomes can work on the same mRNA strand, forming a polyribosome or polysome.
在蛋白质合成过程中，信使RNA（mRNA）将遗传密码从细胞核带到核糖体。转运RNA（tRNA）随后携带特定氨基酸到达核糖体，在那里氨基酸按正确顺序连接形成多肽链。多个核糖体可同时作用于同一条mRNA链，形成多聚核糖体。
8. Chloroplasts and Photosynthesis | 叶绿体与光合作用
Chloroplasts are organelles found in plant cells and some algae that carry out photosynthesis. They contain the pigment chlorophyll, which captures light energy. The overall balanced chemical equation for photosynthesis is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, in the presence of light and chlorophyll.
叶绿体是植物细胞和某些藻类中进行光合作用的细胞器。它们含有叶绿素色素，能捕获光能。光合作用的总平衡化学方程式为：6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂，需要光和叶绿素的参与。
Inside a chloroplast, there are stacks of membrane discs called grana (singular: granum) where the light-dependent reactions take place. The stroma, a fluid-filled space, is where the light-independent reactions (Calvin cycle) occur. Chloroplasts, like mitochondria, have their own DNA and ribosomes, supporting the endosymbiotic theory.
在叶绿体内部，有称为基粒的膜盘堆叠体，是光依赖反应的发生场所。基质是一种充满液体的空间，是光不依赖反应（卡尔文循环）的发生地。与线粒体类似，叶绿体也有自身的DNA和核糖体，这支持了内共生假说。
9. Cell Wall and Vacuole | 细胞壁与液泡
The plant cell wall is a protective layer outside the cell membrane, made mainly of cellulose fibres embedded in a matrix of other polysaccharides and proteins. It provides rigidity, supports the plant, and protects against mechanical damage. The cell wall is fully permeable, unlike the cell membrane.
植物细胞壁是细胞膜外的保护层，主要由纤维素微纤维嵌入其他多糖和蛋白质的基质中构成。它提供刚性，支撑植物体，并防止机械损伤。与细胞膜不同，细胞壁是全透性的。
A large central vacuole is present in mature plant cells, surrounded by a membrane called the tonoplast. It contains cell sap—a solution of water, salts, sugars, and pigments. The vacuole maintains turgor pressure, keeping the cell firm and supporting herbaceous plants. It also stores metabolic waste and can sequester toxins to defend against herbivores.
成熟植物细胞中含有一个大液泡，由液泡膜包围。液泡内含有细胞液——由水、盐、糖和色素组成的溶液。大液泡维持膨压，使细胞保持坚挺，支撑草本植物。它还储存代谢废物，并可隔离毒素以防御植食动物。
10. Microscopy and Magnification Calculations | 显微镜与放大倍数计算
Microscopy is essential for studying cell structure. In the IGCSE AQA syllabus, you must be able to use light microscopes, understand the concept of magnification and resolution, and perform magnification calculations using the formula: Magnification = Image size / Actual size.
显微镜是研究细胞结构必不可少的工具。在 IGCSE AQA 考纲中，同学们必须能够使用光学显微镜，理解放大倍数与分辨率的概念，并使用公式：放大倍数 = 图像尺寸 / 实际尺寸 进行计算。
Resolution is the ability to distinguish between two separate points. A light microscope has a maximum resolution of about 0.2 µm and a maximum useful magnification around ×1500. To calculate actual size, rearrange the formula: Actual size = Image size / Magnification. You must be comfortable converting units, for example 1 mm = 1000 µm.
分辨率是指区分两个独立点的能力。光学显微镜的最大分辨率约为0.2 µm，有效放大倍数约为×1500。要计算实际尺寸，需变换公式：实际尺寸 = 图像尺寸 / 放大倍数。同学们必须熟练掌握单位换算，如 1 mm = 1000 µm。
When drawing cells observed under the microscope, include a title, magnification, and label structures with straight lines. Do not use arrowheads. Include a scale bar where required. Your diagram should show only what you actually see, not what you expect to see, and should be drawn in pencil with clear, unbroken lines.
绘制显微镜下观察到的细胞图时，应包含标题、放大倍数，并用直尺引出直线标注结构，不要使用箭头。如需要，应包含比例尺。图谱只能展示实际观察到的内容，而非凭想象绘制的内容，应用铅笔绘制，线条清晰且不间断。
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