📚 IGCSE Edexcel Biology: Cell Organelles – Essential Exam Guide | IGCSE Edexcel 生物：细胞器考点精讲
In IGCSE Edexcel Biology, understanding cell organelles is fundamental to grasping how cells function, whether in animals, plants or bacteria. This article breaks down each organelle’s structure and role, highlights differences between cell types, and provides exam-focused tips to help you score top marks.
在 IGCSE Edexcel 生物学中，理解细胞器是掌握动物、植物和细菌细胞功能的基础。本文分解每种细胞器的结构和作用，突出不同细胞类型之间的差异，并以考试为导向的技巧，助你取得高分。
1. Introduction to Cell Organelles | 细胞器概述
All living organisms are composed of cells, and within these cells are specialized structures called organelles. Each organelle performs a specific function essential for the cell’s survival, growth and reproduction. IGCSE Edexcel Biology expects you to identify key organelles, describe their functions, and compare their presence in animal, plant and bacterial cells.
所有生物体都由细胞组成，细胞内含有称为细胞器的特化结构。每种细胞器执行特定的功能，对细胞的生存、生长和繁殖至关重要。IGCSE Edexcel 生物学要求你识别关键细胞器，描述其功能，并比较它们在动物、植物和细菌细胞中的存在情况。
Organelles can be membrane-bound (e.g., nucleus, mitochondria) or non-membrane-bound (e.g., ribosomes). Understanding their roles will also help you explain physiological processes such as respiration, photosynthesis and protein synthesis.
细胞器可分为膜结合的（如细胞核、线粒体）和非膜结合的（如核糖体）。理解它们的作用还有助于你解释呼吸、光合作用和蛋白质合成等生理过程。
2. The Nucleus: Control Centre | 细胞核：控制中心
The nucleus is the largest organelle in eukaryotic cells and is surrounded by a double membrane called the nuclear envelope. The envelope contains nuclear pores that regulate the exchange of materials (e.g., mRNA, proteins) between the nucleus and the cytoplasm. Inside, the nucleus contains chromatin, which is DNA wrapped around histone proteins, and a nucleolus, which produces ribosomal RNA and assembles ribosome subunits.
细胞核是真核细胞中最大的细胞器，由称为核膜的双层膜包裹。核膜上有核孔，调控物质（如 mRNA、蛋白质）在细胞核与细胞质之间的交换。核内含有染色质，即缠绕在组蛋白上的 DNA，以及核仁，核仁能产生核糖体 RNA 并组装核糖体亚基。
The nucleus stores the cell’s genetic information and controls cellular activities by regulating gene expression. In exam diagrams, it is often shown as a large, dark-staining spherical structure. Note that bacterial cells do not have a nucleus; their DNA lies free in the cytoplasm.
细胞核储存细胞的遗传信息，并通过调节基因表达来控制细胞活动。在考试示意图中，它通常表现为一个大型、深色的球形结构。注意，细菌细胞没有细胞核；它们的 DNA 游离在细胞质中。
3. Mitochondria: Powerhouse of the Cell | 线粒体：细胞的能量工厂
Mitochondria (singular: mitochondrion) are sausage-shaped organelles with a smooth outer membrane and a highly folded inner membrane. The folds, called cristae, increase the surface area for the enzymes involved in aerobic respiration. The fluid inside is known as the matrix, containing enzymes, mitochondrial DNA and ribosomes.
线粒体（单数：mitochondrion）是腊肠形的细胞器，有光滑的外膜和高度折叠的内膜。这些折叠称为嵴，增加了参与有氧呼吸的酶的表面积。内部的液体叫做基质，含有酶、线粒体 DNA 和核糖体。
Mitochondria are the site of aerobic respiration, where glucose is broken down in the presence of oxygen to release energy in the form of ATP. The reaction can be summarised as:
线粒体是有氧呼吸的场所，在此葡萄糖在有氧条件下被分解，以 ATP 的形式释放能量。该反应可概括为：
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP)
Cells with high energy demands, such as muscle and sperm cells, contain many mitochondria. In IGCSE exams, you may be asked to relate the number of mitochondria to a cell’s activity.
能量需求高的细胞，如肌肉细胞和精子细胞，含有许多线粒体。在 IGCSE 考试中，可能会要求你将线粒体数量与细胞活动联系起来。
4. Ribosomes: Protein Factories | 核糖体：蛋白质工厂
Ribosomes are small organelles made of ribosomal RNA (rRNA) and protein. They are not membrane-bound and are found either floating freely in the cytoplasm or attached to the rough endoplasmic reticulum. Each ribosome consists of a large and a small subunit.
核糖体是由核糖体 RNA（rRNA）和蛋白质组成的小型细胞器。它们无膜结构，可游离于细胞质中，或附着在粗面内质网上。每个核糖体由一个大亚基和一个小亚基构成。
The function of ribosomes is to synthesise proteins by translating the sequence of mRNA into a polypeptide chain. This process is called translation. Ribosomes in the cytoplasm produce proteins for use inside the cell, while those on the RER make proteins for export or incorporation into membranes.
核糖体的功能是通过将 mRNA 序列翻译成多肽链来合成蛋白质。这一过程称为翻译。细胞质中的核糖体产生供细胞内部使用的蛋白质，而粗面内质网上的核糖体则制造用于输出或嵌入膜的蛋白质。
In bacterial cells, ribosomes are smaller (70S) compared to the 80S ribosomes in eukaryotes. This difference is a key point for comparison.
在细菌细胞中，核糖体比真核生物的 80S 核糖体小（70S），这一差异是比较的关键点。
5. Endoplasmic Reticulum: Transport Network | 内质网：运输网络
The endoplasmic reticulum (ER) is a network of interconnected membrane-bound sacs and tubules. There are two types: rough ER and smooth ER. Rough ER is studded with ribosomes on its cytoplasmic surface, giving it a ‘rough’ appearance, while smooth ER lacks ribosomes.
内质网（ER）是相互连接的膜质囊状和管状网络。分为两种类型：粗面内质网和滑面内质网。粗面内质网在细胞质一侧附着有核糖体，使其外观“粗糙”，而滑面内质网则无核糖体。
Rough ER is involved in folding, modifying and transporting proteins synthesised by its attached ribosomes. Smooth ER is associated with lipid synthesis, carbohydrate metabolism and detoxification of drugs and poisons. In cells specialised for lipid production, such as those in the liver, smooth ER is abundant.
粗面内质网参与折叠、修饰并转运由其附着核糖体合成的蛋白质。滑面内质网则与脂质合成、碳水化合物代谢以及药物和毒物的解毒有关。在特化于脂质生产的细胞（如肝细胞）中，滑面内质网含量丰富。
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