📚 Cell Structure | 细胞结构
Cells are the basic structural and functional units of all living organisms. Understanding cell structure is essential for explaining how organisms grow, reproduce, obtain energy and maintain homeostasis. This article covers the main organelles, the differences between animal and plant cells, and how microscopy is used to observe them.
细胞是所有生物体结构和功能的基本单位。理解细胞结构对于解释生物体如何生长、繁殖、获取能量和维持内稳态至关重要。本文介绍主要细胞器、动植物细胞的差异以及如何使用显微镜观察细胞。
1. The Cell Theory | 细胞学说
The cell theory states that all living things are made of cells, the cell is the basic unit of structure and function, and all cells arise from pre-existing cells by cell division. This theory was developed through the work of scientists such as Robert Hooke, Anton van Leeuwenhoek, Matthias Schleiden, Theodor Schwann and Rudolf Virchow.
细胞学说指出，所有生物体都由细胞构成，细胞是结构和功能的基本单位，所有细胞都来自已有细胞的分裂。这一理论由 Robert Hooke、Anton van Leeuwenhoek、Matthias Schleiden、Theodor Schwann 和 Rudolf Virchow 等科学家的工作逐步建立。
Organisms may be unicellular, such as bacteria and yeast, or multicellular, such as plants and animals. In multicellular organisms, cells become specialised to perform different functions.
生物体可以是单细胞的，例如细菌和酵母，也可以是多细胞的，例如植物和动物。在多细胞生物中，细胞发生特化以执行不同功能。
2. Prokaryotic and Eukaryotic Cells | 原核细胞与真核细胞
Cells are divided into two main types: prokaryotic and eukaryotic. Prokaryotic cells, such as bacteria, lack a true nucleus and membrane-bound organelles; their DNA is a single circular molecule located in the cytoplasm. Eukaryotic cells, including animal, plant, fungal and protist cells, have a distinct nucleus and membrane-bound organelles.
细胞分为两大类：原核细胞和真核细胞。原核细胞（如细菌）没有真正的细胞核和膜性细胞器；其DNA是一条位于细胞质中的单链环状分子。真核细胞包括动物、植物、真菌和原生生物细胞，具有明显的细胞核和膜性细胞器。
| Feature | 特征 | Prokaryotic | 原核 | Eukaryotic | 真核 |
|---|---|---|
| Nucleus | 细胞核 | Absent | 无 | Present | 有 |
| Membrane-bound organelles | 膜性细胞器 | Absent | 无 | Present | 有 |
| Ribosomes | 核糖体 | 70S | 70S | 80S | 80S |
| DNA | DNA | Circular, in cytoplasm | 环状，在细胞质中 | Linear, in nucleus | 线状，在细胞核中 |
| Size | 大小 | Smaller, 0.1-5 μm | 较小，0.1-5 μm | Larger, 10-100 μm | 较大，10-100 μm |
Both prokaryotic and eukaryotic cells have a cell membrane, cytoplasm and ribosomes, so these structures are common to all cells. However, the detailed organisation differs greatly.
原核细胞和真核细胞都有细胞膜、细胞质和核糖体，因此这些结构是所有细胞共有的。然而，细胞的具体组织方式差异很大。
3. Animal Cell Structures | 动物细胞结构
A typical animal cell contains a cell membrane, cytoplasm, nucleus, mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes and small temporary vacuoles. It does not have a cell wall, chloroplasts or a large permanent vacuole.
典型的动物细胞含有细胞膜、细胞质、细胞核、线粒体、核糖体、内质网、高尔基体、溶酶体和临时的小液泡。它没有细胞壁、叶绿体或大的永久液泡。
The cell membrane controls the movement of substances into and out of the cell. The cytoplasm is the site of many metabolic reactions, and it contains dissolved nutrients and organelles.
细胞膜控制物质进出细胞。细胞质是许多代谢反应发生的场所，其中含有溶解的营养物质和细胞器。
4. Plant Cell Structures | 植物细胞结构
A typical plant cell has all the organelles found in an animal cell except lysosomes (rare in plants), plus a cellulose cell wall, chloroplasts, and a large permanent vacuole containing cell sap. The cell wall provides shape and support, while the vacuole maintains turgor pressure.
典型的植物细胞除溶酶体（植物中少见）外，具有动物细胞中的所有细胞器，另外还有由纤维素构成的细胞壁、叶绿体和含有细胞液的大液泡。细胞壁提供形状和支撑，液泡维持膨压。
Chloroplasts contain chlorophyll and are responsible for photosynthesis. The large permanent vacuole stores water, ions, pigments and waste products, and helps keep the cell firm.
叶绿体含有叶绿素，负责光合作用。大的永久液泡储存水分、离子、色素和代谢废物，并帮助保持细胞坚挺。
5. Cell Membrane and Transport | 细胞膜与物质运输
The cell membrane is a partially permeable barrier made of a phospholipid bilayer with embedded proteins. It allows small, non-polar molecules to pass freely but restricts the movement of large or charged particles unless transport proteins are involved.
细胞膜是由磷脂双分子层和嵌入其中的蛋白质组成的部分通透性屏障。它允许小的非极性分子自由通过，但限制大分子或带电颗粒的移动，除非有转运蛋白参与。
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. Osmosis is the diffusion of water molecules through a partially permeable membrane from a dilute solution to a more concentrated solution.
扩散是粒子从浓度较高的区域向浓度较低的区域净移动，即顺浓度梯度移动。渗透是水分子通过部分通透性膜从稀溶液向较浓溶液扩散的过程。
Active transport moves substances against a concentration gradient, from low to high concentration, using energy from ATP. This is how root hair cells absorb mineral ions from the soil.
主动运输逆浓度梯度将物质从低浓度区域运往高浓度区域，需要消耗ATP释放的能量。根毛细胞就是通过主动运输从土壤中吸收矿质离子的。
6. Nucleus and Genetic Material | 细胞核与遗传物质
The nucleus is the control centre of the eukaryotic cell. It contains most of the cell's genetic material in the form of chromosomes, which are made of DNA wrapped around histone proteins. The nuclear envelope has pores that allow mRNA and other molecules to move between the nucleus and cytoplasm.
细胞核是真核细胞的控制中心。它含有细胞的大部分遗传物质，以染色体的形式存在，染色体由DNA缠绕组蛋白构成。核膜上有核孔，允许mRNA和其他分子在细胞核与细胞质之间移动。
The nucleolus is a region inside the nucleus where ribosomal RNA is synthesised and ribosomal subunits are assembled. During cell division, chromosomes condense and become visible under a light microscope.
核仁是细胞核内的一个区域，负责合成核糖体RNA并组装核糖体亚基。在细胞分裂过程中，染色体浓缩，并在光学显微镜下变得可见。
7. Mitochondria and Energy | 线粒体与能量
Mitochondria are the sites of aerobic respiration, where glucose and oxygen are used to produce ATP, the cell's energy currency. They have a double membrane: the inner membrane is folded into cristae to increase surface area for ATP production.
线粒体是有氧呼吸的场所，在这里葡萄糖和氧气被用来产生ATP，即细胞的能量货币。线粒体具有双层膜：内膜向内折叠形成嵴，以增加ATP产生的表面积。
Cells with high energy demands, such as muscle cells and sperm cells, contain large numbers of mitochondria. The matrix inside mitochondria contains enzymes for the Krebs cycle and mitochondrial DNA.
能量需求高的细胞，如肌肉细胞和精子细胞，含有大量线粒体。线粒体基质中含有参与三羧酸循环的酶和线粒体DNA。
8. Chloroplasts and Photosynthesis | 叶绿体与光合作用
Chloroplasts are the organelles where photosynthesis occurs in plant cells and algae. They contain chlorophyll, which absorbs light energy, and have internal membrane stacks called grana, surrounded by the stroma.
叶绿体是植物细胞和藻类中进行光合作用的细胞器。它们含有吸收光能的叶绿素，内部有称为基粒的膜堆，周围是基质。
Photosynthesis can be summarised by the word equation:
光合作用可以用文字方程式概括：
carbon dioxide + water → glucose + oxygen
二氧化碳 + 水 → 葡萄糖 + 氧气
The glucose produced may be used in respiration, stored as starch, or used to build cellulose.
产生的葡萄糖可用于呼吸作用、以淀粉形式储存，或用于合成纤维素。
9. Ribosomes and Protein Synthesis | 核糖体与蛋白质合成
Ribosomes are small organelles made of ribosomal RNA and protein. They are the sites of protein synthesis, where amino acids are joined together in the order specified by messenger RNA. Ribosomes may be free in the cytoplasm or attached to the rough endoplasmic reticulum.
核糖体是由核糖体RNA和蛋白质组成的小型细胞器。它们是蛋白质合成的场所，按照信使RNA指定的顺序将氨基酸连接起来。核糖体可以游离在细胞质中，也可以附着在粗面内质网上。
Proteins made on free ribosomes are usually used inside the cell, while proteins made on the rough ER are often secreted or sent to the cell membrane. The rough ER has ribosomes on its surface, giving it a rough appearance.
游离核糖体上合成的蛋白质通常在细胞内使用，而粗面内质网上合成的蛋白质往往被分泌出细胞或运送到细胞膜。粗面内质网表面附有核糖体，因此外观粗糙。
10. Endomembrane System and Vesicles | 内膜系统与囊泡
The endoplasmic reticulum and Golgi apparatus form part of the cell's endomembrane system. The rough ER folds and modifies newly synthesised proteins, while the smooth ER synthesises lipids and detoxifies certain chemicals.
内质网和高尔基体是细胞内膜系统的一部分。粗面内质网对新合成的蛋白质进行折叠和修饰，而滑面内质网合成脂质并解毒某些化学物质。Published by TutorHao | Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图