The Cell | 细胞

📚 The Cell | 细胞

Every living organism is made of cells. In the Edexcel IGCSE Biology course, you need to understand the structure of cells, the function of each organelle, and the differences between animal, plant, and bacterial cells. This article will guide you through these key ideas step by step.

每一个活的生物体都由细胞构成。在 Edexcel IGCSE 生物课程中，你需要理解细胞的结构、每种细胞器的功能，以及动物细胞、植物细胞和细菌细胞之间的区别。这篇文章会一步一步带你掌握这些关键内容。

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1. Cell Theory | 细胞学说

Cell theory states that all living things are made of cells. Cells are the basic unit of life. In some modern versions, cell theory also says that all cells come from pre-existing cells, and that genetic information is passed from parent cell to daughter cell.

细胞学说指出，一切生物体都是由细胞构成的。细胞是生命的基本单位。在现代版本的细胞学说中，还认为所有细胞都来自原有细胞，并且遗传信息会从母细胞传递给子细胞。

This theory is important because it unifies all branches of biology. Whether you study a bacterium, an oak tree, or a human, you are studying cells.

这个学说非常重要，因为它把生物学的各个分支联系在了一起。无论你研究细菌、橡树还是人类，你实际上都在研究细胞。

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2. Eukaryotic and Prokaryotic Cells | 真核细胞与原核细胞

Living organisms can be divided into two major groups based on their cell structure: eukaryotes and prokaryotes. Eukaryotic cells have a true nucleus enclosed by a membrane. Prokaryotic cells do not have a membrane-bound nucleus.

根据细胞结构的不同，生物体可以被分成两大类：真核生物和原核生物。真核细胞有被膜包被的真正细胞核，而原核细胞没有膜包被的细胞核。

Animals, plants, and fungi are eukaryotic. Bacteria are prokaryotic. In the Edexcel IGCSE syllabus, you need to be able to compare eukaryotic and prokaryotic cells and identify features such as plasmids in bacteria.

动物、植物和真菌都属于真核生物，细菌属于原核生物。在 Edexcel IGCSE 考纲中，你需要能够比较真核细胞和原核细胞，并辨认细菌中是否含有质粒等特征。

Prokaryotic cells normally contain a single circular chromosome of DNA. They may also contain small rings of DNA called plasmids. They do not have mitochondria or chloroplasts, and their ribosomes are smaller than eukaryotic ribosomes.

原核细胞通常含有一个环状的 DNA 染色体，还可能含有称为质粒的小型环状 DNA。原核细胞没有线粒体或叶绿体，它们的核糖体比真核细胞的核糖体更小。

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3. Animal Cell Structure | 动物细胞结构

A typical animal cell contains a nucleus, cell membrane, cytoplasm, mitochondria, and ribosomes. These structures are often called subcellular structures because they are inside the cell.

一个典型的动物细胞含有细胞核、细胞膜、细胞质、线粒体和核糖体。这些结构通常被称为亚细胞结构，因为它们位于细胞内部。

The nucleus contains chromosomes made of DNA and controls the activities of the cell. The cell membrane controls what enters and leaves the cell. The cytoplasm is a jelly-like substance where many metabolic reactions occur.

细胞核含有由 DNA 组成的染色体，并控制着细胞的活动。细胞膜控制物质进出细胞。细胞质是一种胶状物质，许多代谢反应都在其中进行。

Mitochondria are the site of aerobic respiration. They release energy from glucose in the form of ATP. Ribosomes are the site of protein synthesis. They can be free in the cytoplasm or attached to membranes.

线粒体是有氧呼吸的场所，它们从葡萄糖中释放能量并生成 ATP。核糖体是蛋白质合成的场所，它们可以游离在细胞质中，也可以附着在膜结构上。

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4. Plant Cell Structure | 植物细胞结构

Plant cells have all the structures that animal cells have, but they also contain three extra structures: a cellulose cell wall, chloroplasts, and a permanent vacuole.

植物细胞拥有动物细胞的所有结构，但还额外含有三种结构：纤维素细胞壁、叶绿体和永久性液泡。

The cell wall is made of cellulose. It provides strength and support and gives the cell a fixed shape. It is fully permeable, meaning water and dissolved substances can pass through it freely.

细胞壁由纤维素构成，它提供强度和支持，并让细胞保持固定的形状。细胞壁是完全通透的，水和溶解的物质可以自由通过。

Chloroplasts contain a green pigment called chlorophyll. Chlorophyll absorbs light energy for photosynthesis. The permanent vacuole contains cell sap and helps keep the cell rigid by providing turgor pressure.

叶绿体含有一种称为叶绿素的绿色色素。叶绿素吸收光能用于光合作用。永久性液泡含有细胞液，并通过提供膨胀压使细胞保持坚挺。

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5. Organelles and Their Functions | 细胞器及其功能

You need to be able to match each organelle to its function. This is a common question in IGCSE Biology exams.

你需要能够把每种细胞器和它的功能对应起来，这是 IGCSE 生物考试中的常见题型。

• Nucleus: contains genetic material and controls the cell. 细胞核：含有遗传物质，控制细胞活动。

• Cell membrane: controls the entry and exit of substances. 细胞膜：控制物质的进出。

• Cytoplasm: site of most chemical reactions. 细胞质：大部分化学反应的场所。

• Mitochondria: site of aerobic respiration. 线粒体：有氧呼吸的场所。

• Ribosomes: site of protein synthesis. 核糖体：蛋白质合成的场所。

• Cell wall: provides support and strength. 细胞壁：提供支持与强度。

• Chloroplasts: site of photosynthesis. 叶绿体：光合作用的场所。

• Permanent vacuole: stores cell sap and maintains turgor. 永久性液泡：储存细胞液，维持膨胀压。

In an exam, you may be asked to name an organelle from a description. Practise rewriting each function in your own words, as this helps you remember the details accurately.

在考试中，你可能会被要求根据描述写出细胞器的名称。试着用自己的话复述每一个功能，这样能帮助你更准确地记住细节。

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6. Animal vs Plant Cells | 动物细胞与植物细胞的比较

The main differences between animal and plant cells are often tested in a comparison table. You should know which structures are present or absent in each type of cell.

动物细胞和植物细胞的主要区别经常以比较表格的形式进行考查。你应该清楚每种结构中哪些存在，哪些不存在。

Structure	Animal cell	Plant cell
Nucleus | 细胞核	Present | 有	Present | 有
Cell membrane | 细胞膜	Present | 有	Present | 有
Mitochondria | 线粒体	Present | 有	Present | 有
Ribosomes | 核糖体	Present | 有	Present | 有
Cell wall | 细胞壁	Absent | 无	Present | 有
Chloroplasts | 叶绿体	Absent | 无	Present | 有
Permanent vacuole | 永久性液泡	Absent | 无	Present | 有

Plant cells also tend to have a regular, rectangular shape because the cell wall restricts how the cell expands. Animal cells are usually more irregular in shape because they only have a flexible cell membrane.

植物细胞通常呈规则的长方形，因为细胞壁限制了细胞扩张的方式。动物细胞通常形状更不规则，因为它们只有一层柔韧的细胞膜。

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7. Bacterial Cells | 细菌细胞

Bacterial cells are prokaryotic. They are much smaller than animal and plant cells, and they have a simpler structure. You need to be able to identify the structures found in a bacterial cell.

细菌细胞属于原核细胞。它们比动物细胞和植物细胞小得多，结构也更简单。你需要能够辨认细菌细胞中的结构。

A bacterial cell has a cell wall, but it is not made of cellulose. Instead, it is made of a different substance called peptidoglycan. Bacterial cells also have a cell membrane, cytoplasm, and ribosomes.

细菌细胞有细胞壁，但它的细胞壁不是由纤维素构成的，而是由一种称为肽聚糖的物质构成。细菌细胞也有细胞膜、细胞质和核糖体。

Bacteria do not have a nucleus. Their genetic material is a single circular DNA loop. They may also have one or more plasmids, which are small circular DNA molecules. Some bacteria have a flagellum, which helps them move.

细菌没有细胞核，它们的遗传物质是一个环状 DNA 分子。它们也可能有一个或多个质粒，质粒是小型的环状 DNA 分子。有些细菌还有鞭毛，用于帮助它们运动。

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8. Specialised Cells | 特化细胞

In multicellular organisms, cells are specialised to carry out particular functions. This is called differentiation. Edexcel IGCSE Biology asks you to link the structure of a specialised cell to its function.

在多细胞生物体中，细胞会发生特化以执行特定功能，这一过程称为分化。Edexcel IGCSE 生物要求你能够把特化细胞的结构和功能联系起来。

For example, red blood cells are biconcave discs with no nucleus. Their shape increases the surface area for absorbing oxygen, and the lack of a nucleus leaves more room for haemoglobin.

例如，红细胞呈双凹圆盘状，没有细胞核。这种形状增加了与氧气结合的表面积，而缺少细胞核为血红蛋白留出了更多空间。

Root hair cells have a long, thin extension called a root hair. This increases the surface area for absorbing water and mineral ions from the soil. They also have many mitochondria to release energy for active transport.

根毛细胞有一个称为根毛的细长突起，这增大了从土壤中吸收水分和矿物质的表面积。它们还有很多线粒体，为主动运输提供能量。

Sperm cells have a tail, or flagellum, to swim towards the egg cell. They are packed with mitochondria to provide energy for movement. The acrosome contains enzymes that help the sperm penetrate the egg.

精子细胞有尾巴，也就是鞭毛，用于游向卵细胞。精子内含有大量线粒体，为运动提供能量。顶体含有酶，帮助精子进入卵细胞。

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9. Levels of Organisation | 细胞的分化与组织层次

Cells are not the only level of organisation. In the Edexcel IGCSE course, you need to know the order: cells, tissues, organs, organ systems, and organism.

细胞并不是唯一的组织层次。在 Edexcel IGCSE 课程中，你需要知道以下顺序：细胞、组织、器官、器官系统和生物体。

A tissue is a group of similar cells working together to perform a function. For example, muscle tissue is made of muscle cells that can contract. Xylem tissue transports water through a plant.

组织是一群相似细胞共同完成某种功能的结构。例如，肌肉组织由能够收缩的肌肉细胞构成。木质部组织在植物中运输水分。

An organ contains several types of tissue working together. The heart is an organ made of muscle tissue, nervous tissue, and connective tissue. A leaf is an organ made of epidermal tissue, palisade tissue, and vascular tissue.

器官由多种组织共同构成。心脏是一个器官，由肌肉组织、神经组织和结缔组织构成。叶片是器官，由表皮组织、栅栏组织和维管组织构成。

An organ system is a group of organs that work together. The digestive system includes the stomach, small intestine, and large intestine. The circulatory system includes the heart and blood vessels.

器官系统是一组共同工作的器官。消化系统包括胃、小肠和大肠。循环系统包括心脏和血管。

Cell → Tissue → Organ → Organ system → Organism

细胞 → 组织 → 器官 → 器官系统 → 生物体

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10. Microscopy and Cell Measurement | 显微镜与细胞测量

Most cells are too small to be seen with the naked eye. A light microscope can be used to see nuclei, chloroplasts, and cell walls, but an electron microscope gives much higher magnification and resolution.

大多数细胞太小，肉眼无法看见。光学显微镜可以用来观察细胞核、叶绿体和细胞壁，但电子显微镜能提供更高的放大倍数和分辨率。

In exams, you need to remember the units for cell measurements. The metre is too large, so we use smaller units:

在考试中，你需要记住细胞测量的单位。米太大，因此我们使用更小的单位：

1 mm = 1000 μm

1 μm = 1000 nm

The magnification of a microscope can be calculated using the formula:

显微镜的放大倍数可以通过以下公式计算：

Magnification = Image size ÷ Actual size

放大倍数 = 图像大小 ÷ 实际大小

If a drawing of a cell is 20 mm long and the real cell is 0.5 mm long, the magnification is 20 ÷ 0.5 = 40×. Always make sure that both values are in the same unit before calculating.

如果某个细胞图的长度是 20 mm，而实际细胞长度是 0.5 mm，那么放大倍数就是 20 ÷ 0.5 = 40×。计算前一定要确保两个数值使用相同单位。

An electron microscope allows us to see organelles which are too small for a light microscope, such as ribosomes and the internal structure of mitochondria. This is why electron micrographs show much finer detail than light micrographs.

电子显微镜让我们能看到光学显微镜下无法看到的细胞器，例如核糖体和线粒体的内部结构。这就是为什么电子显微照片比光学显微照片展示出更多细节。

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11. Summary and Exam Tips | 总结与考试提示

Cell biology is a foundation for many other topics in IGCSE Biology. Make sure you can draw and label animal, plant, and bacterial cells, and explain the function of each structure without looking at your notes.

细胞生物学是 IGCSE 生物中许多其他主题的基础。请确保你能够画出并标注动物细胞、植物细胞和细菌细胞，并且在不看笔记的情况下解释每种结构的功能。

• Use the exact terms: nucleus, cytoplasm, cell membrane, mitochondria, ribosomes, chloroplast, cell wall, vacuole. 请使用准确术语：细胞核、细胞质、细胞膜、线粒体、核糖体、叶绿体、细胞壁、液泡。

• Learn which structures are found only in plant cells. 记住哪些结构只存在于植物细胞中。

• Practise magnification calculations and unit conversions. 练习放大倍数计算和单位换算。

• Connect every specialised cell structure to its function. 把每一种特化细胞的结构和功能联系起来。

By understanding cells, you prepare yourself for later topics such as diffusion, osmosis, active transport, photosynthesis, and respiration. The cell is truly the starting point of everything in biology.

理解了细胞，你也就为后续的扩散、渗透、主动运输、光合作用和呼吸作用等主题做好了准备。细胞确实是生物学中一切知识的起点。

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