📚 GCSE CIE Biology: Organelles Key Points | GCSE CIE 生物：细胞器考点精讲
In GCSE CIE Biology, a solid understanding of cell organelles is essential. This article breaks down the key organelles, their structures, and functions, comparing animal, plant, and prokaryotic cells.
在 GCSE CIE 生物中，透彻理解细胞器至关重要。本文逐一剖析关键细胞器、其结构与功能，并比较动物细胞、植物细胞和原核细胞。
1. What Are Organelles? | 细胞器是什么？
Organelles are specialised subunits within a cell that carry out specific metabolic tasks. In eukaryotic cells, most organelles are membrane-bound, which compartmentalises reactions and increases efficiency.
细胞器是细胞内执行特定代谢任务的专门亚单位。在真核细胞中，大多数细胞器由膜包裹，这种区隔化使反应更为高效。
Key examples include the nucleus, mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, and, in plant cells, chloroplasts and a large permanent vacuole.
典型例子包括细胞核、线粒体、核糖体、内质网、高尔基体，以及植物细胞中的叶绿体和中央大液泡。
2. Nucleus | 细胞核
The nucleus is the control centre of the cell, surrounded by a double membrane called the nuclear envelope.
细胞核是细胞的控制中心，由称为核膜的双层膜包裹。
Nuclear pores in the envelope allow messenger RNA (mRNA) and other molecules to exit into the cytoplasm, while allowing proteins to enter.
核膜上的核孔允许信使 RNA (mRNA) 及其他分子进入细胞质，同时让蛋白质进入核内。
Inside, chromatin (DNA wrapped around histone proteins) carries the genetic code. During cell division, chromatin condenses into distinct chromosomes.
核内染色质（DNA 缠绕组蛋白）携带遗传密码。细胞分裂时，染色质凝聚为可见的染色体。
The nucleolus is a dense region within the nucleus where ribosomal RNA is synthesised and ribosomal subunits are assembled.
核仁是核内致密区域，在此合成核糖体 RNA 并组装核糖体亚基。
3. Mitochondria | 线粒体
Mitochondria are the site of aerobic respiration, where energy stored in glucose is released and packaged as ATP.
线粒体是有氧呼吸的场所，葡萄糖中储存的能量在此释放并以 ATP 形式储存。
Each mitochondrion has a smooth outer membrane and a highly folded inner membrane. The folds, called cristae, provide a large surface area for enzymes of the electron transport chain.
每个线粒体有平滑的外膜和高度折叠的内膜。这些折叠称为嵴，为电子传递链的酶提供了巨大表面积。
The fluid interior, the matrix, contains enzymes for the link reaction and the Krebs cycle. Mitochondria also possess their own circular DNA and 70S ribosomes, allowing them to synthesise some proteins independently.
内部的液态基质含有连接反应和三羧酸循环的酶。线粒体还具有自身的环状 DNA 和 70S 核糖体，可独立合成部分蛋白质。
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ ATP)
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ 能量/ATP)
4. Ribosomes | 核糖体
Ribosomes are non-membrane-bound organelles composed of ribosomal RNA (rRNA) and protein. They are the sites of translation, where amino acids are linked together to form polypeptide chains.
核糖体是无膜细胞器，由核糖体 RNA (rRNA) 和蛋白质构成。它们是翻译的场所，氨基酸在此连接成多肽链。
In eukaryotic cells, ribosomes either float freely in the cytoplasm or attach to the rough endoplasmic reticulum. Free ribosomes typically synthesise proteins for use within the cell, while bound ribosomes produce proteins destined for secretion or insertion into membranes.
在真核细胞中，核糖体或悬浮于细胞质中，或附着在粗面内质网上。游离核糖体多合成细胞自身使用的蛋白质，附着核糖体则合成供分泌或嵌入膜的蛋白质。
Eukaryotic ribosomes are 80S (composed of 60S and 40S subunits). Prokaryotic ribosomes are 70S, a difference that is exploited by certain antibiotics.
真核生物核糖体为 80S（由 60S 和 40S 亚基组成）。原核生物核糖体为 70S，某些抗生素正是利用了这一差异。
5. Endoplasmic Reticulum | 内质网
The endoplasmic reticulum (ER) is a network of interconnected flattened sacs and tubules continuous with the nuclear envelope. It comes in two forms: rough and smooth.
内质网是与核膜相连的扁平囊和管道网络，分为粗面和滑面两种。
Rough ER (RER) is studded with ribosomes on its cytoplasmic surface. Newly synthesised proteins enter the RER lumen, where they are folded, modified (e.g. by addition of sugar chains), and packaged into transport vesicles.
粗面内质网 (RER) 胞质面附着大量核糖体。新合成的蛋白质进入 RER 腔，在此折叠、修饰（如添加糖链）并包裹成运输囊泡。
Smooth ER (SER) lacks ribosomes. It is involved in lipid and steroid hormone synthesis, detoxification of drugs and poisons in liver cells, and storage of calcium ions in muscle cells.
滑面内质网 (SER) 无核糖体，参与脂质与类固醇激素合成，在肝细胞中参与药物和毒素的解毒，在肌细胞中储存钙离子。
6. Golgi Apparatus | 高尔基体
The Golgi apparatus consists of a stack of flattened, membrane-bound cisternae. Its primary role is to receive, modify, sort, and package proteins and lipids that have arrived from the ER.
高尔基体由一叠膜包围的扁平潴泡构成，其主要作用是接收、修饰、分拣并包装来自内质网的蛋白质和脂质。
Vesicles from the ER fuse with the cis face of the Golgi. Inside, enzymes may add or trim carbohydrate chains (glycosylation). The modified molecules are then packaged into secretory vesicles that bud off from the trans face.
来自内质网的囊泡与高尔基体顺面融合。内部酶类可添加或修剪糖链（糖基化）。修饰后的分子包裹成分泌囊泡，从反面出芽离开。
These vesicles can travel to the cell membrane for exocytosis, or to other destinations like lysosomes.
这些囊泡可运往细胞膜进行胞吐，或前往其他目的地如溶酶体。
7. Chloroplasts | 叶绿体
Chloroplasts are found in plant cells and some algae. They are the organelles of photosynthesis, converting light energy into chemical energy stored in glucose.
叶绿体存在于植物细胞和某些藻类中，是光合作用的细胞器，将光能转化为储存在葡萄糖中的化学能。
A chloroplast has a double membrane, internal thylakoid membranes arranged in stacks called grana, and a fluid-filled stroma. Chlorophyll pigments embedded in the thylakoid membranes capture light energy.
叶绿体具有双层膜，内部类囊体膜堆叠成基粒，内部充满液态基质。嵌入类囊体膜的叶绿素捕获光能。
The light-dependent reactions occur on the thylakoid membranes, while the light-independent stage (Calvin cycle) takes place in the stroma.
光反应发生在类囊体膜上，而暗反应（卡尔文循环）在基质中进行。
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
8. Vacuoles | 液泡
Plant cells typically possess a large, central vacuole surrounded by a membrane called the tonoplast. It contains cell sap — a solution of water, mineral salts, sugars, and pigments.
植物细胞通常具有一个被液泡膜包围的大中央液泡，内含细胞液——由水、无机盐、糖类和色素组成的溶液。
This vacuole maintains turgor pressure against the cell wall, keeping herbaceous plants upright. It also stores waste products and can contain enzymes that break down macromolecules.
该液泡维持对细胞壁的膨压，使草本植物保持挺立。它也能储存废物，并含有分解大分子的酶。
Animal cells may contain small, temporary vacuoles, such as food vacuoles or contractile vacuoles, but they lack a large permanent central vacuole.
动物细胞可能含有小的临时性液泡，如食物泡或收缩泡，但缺少永久性中央大液泡。
9. Cell Wall and Cell Membrane | 细胞壁与细胞膜
The cell wall is a rigid layer external to the cell membrane. In plants, it is composed mainly of cellulose fibres embedded in a matrix of other polysaccharides. It provides structural support, prevents osmotic lysis, and maintains cell shape.
细胞壁是细胞膜外的刚性层。在植物中，主要由纤维素微纤丝嵌入其他多糖基质中构成。它提供结构支撑，防止渗透裂解并维持细胞形状。
Fungal cell walls contain chitin, while bacterial cell walls contain peptidoglycan. Note that the cell wall is not classified as an organelle because it is outside the plasma membrane, but it is a crucial structure for cells that possess it.
真菌细胞壁含几丁质，细菌细胞壁含肽聚糖。注意，细胞壁因位于质膜之外而不属于细胞器，但对拥有它的细胞而言极为重要。
The cell membrane (plasma membrane) is found in all cells. It is a partially permeable phospholipid bilayer with embedded proteins, forming a fluid mosaic. It controls the entry and exit of substances via diffusion, osmosis, and active transport.
细胞膜存在于所有细胞中，是嵌有蛋白质的磷脂双分子层，部分通透并形成流动镶嵌结构。它通过扩散、渗透和主动运输控制物质的进出。
10. Organelles in Prokaryotes vs Eukaryotes | 原核与真核细胞的细胞器比较
Prokaryotic cells (e.g. bacteria) lack membrane-bound organelles. Their genetic material is a circular DNA molecule free in the cytoplasm in a region called the nucleoid, along with smaller rings of DNA called plasmids.
原核细胞（如细菌）没有膜包裹的细胞器。其遗传物质为一条环状 DNA，游离在称为拟核的细胞质区域，此外还有较小的 DNA 环——质粒。
Eukaryotic cells (animals, plants, fungi, protists) possess a true nucleus and a wide array of membrane-bound organelles. The table below summarises the differences in organelle presence.
真核细胞（动物、植物、真菌、原生生物）具有真正的细胞核和多种膜包裹的细胞器。下表总结了细胞器存在的差异。
| Organelle / Structure | Prokaryotic Cell | Animal Cell | Plant Cell |
|---|---|---|---|
| Nucleus | Absent; circular DNA in nucleoid | Present | Present |
| Mitochondria | Absent | Present | Present |
| Chloroplasts | Absent | Absent | Present |
| Endoplasmic Reticulum | Absent | Present | Present |
| Golgi Apparatus | Absent | Present | Present |
| Ribosomes | 70S, free in cytoplasm | 80S, free and bound to RER | 80S, free and bound to RER |
| Cell Wall | Present (peptidoglycan) | Absent | Present (cellulose) |
| Large Permanent Vacuole | Absent | Absent | Present |
The fundamental difference is that prokaryotic cells lack membrane-bound organelles, so their biochemical processes occur either in the cytoplasm or on the cell membrane. Eukaryotic cells compartmentalise these processes within organelles, allowing greater complexity and regulation.
根本区别在于，原核细胞没有膜包裹的细胞器，其生化过程发生在细胞质或细胞膜上。真核细胞将这些过程区隔在不同细胞器内，可实现更高的复杂度和调控。
For your GCSE exam: be able to label diagrams of animal and plant cells, identify organelles from descriptions, and explain why organelles are adapted to their functions. Also remember that prokaryotic cells contain ribosomes and cytoplasm but no membrane-bound nucleus or organelles.
GCSE 考试要点：能标注动植物细胞图，根据描述识别细胞器，解释细胞器如何适应其功能。还需记住原核细胞含有核糖体和细胞质，但没有膜包围的细胞核及细胞器。
Published by TutorHao | Biology Revision Series | alevel
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