细胞结构
生物· 2.2–2.6B（2017年第3版）· 12 分钟阅读
1. 核心细胞器：结构与功能★★☆☆☆⏱ 4 min
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所有活细胞都由名为细胞器的小型特化结构组成，每种细胞器都有维持细胞存活和正常运作的特定功能。考试要求你掌握8种核心细胞器的结构与功能。
细胞器
细胞内执行特定功能的特化亚结构。
Organelle | Function |
|---|---|
Nucleus | Contains genetic material (chromosomes/DNA) and controls all cell activities |
Cytoplasm | Gel-like substance where most chemical reactions in the cell take place |
Cell membrane | Partially permeable layer that controls which substances enter and leave the cell |
Cell wall | Rigid cellulose layer surrounding plant cells, provides support and strength |
Mitochondria | Site of aerobic respiration, where energy is released for the cell to use |
Chloroplasts | Found in green plant cells, contain chlorophyll and are the site of photosynthesis |
Ribosomes | Tiny structures in the cytoplasm, site of protein synthesis |
Vacuole | Large permanent structure in plant cells, contains cell sap and maintains cell turgor |
写出负责蛋白质合成的细胞器名称，并列举一种仅存在于植物细胞中的细胞器。
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步骤1：回忆细胞器功能。蛋白质合成发生在核糖体中。
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步骤2：识别植物独有细胞器：正确答案包括纤维素细胞壁、叶绿体或大型永久液泡。
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最终答案：核糖体；叶绿体（或其他符合要求的植物独有细胞器）
2. 动植物细胞对比★★☆☆☆⏱ 3 min
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考试题目中经常要求你找出动植物细胞的异同点。评分标准要求你明确说明植物细胞拥有而动物细胞不具备的结构。
Shared Features (Both Cell Types) | Plant Cell Only Features |
|---|---|
Nucleus | Cellulose cell wall |
Cytoplasm | Chloroplasts |
Cell membrane | Large permanent vacuole |
Mitochondria | |
Ribosomes |
一名学生在显微镜下观察一个细胞，看到了细胞壁、线粒体和一个大液泡。判断该细胞属于植物细胞还是动物细胞，并给出两条理由。
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步骤1：识别独有特征：细胞壁和大型永久液泡仅存在于植物细胞中。
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步骤2：确认共有特征：两种细胞类型都有线粒体，因此该特征不会推翻之前的判断。
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最终答案：植物细胞。理由：它拥有纤维素细胞壁和大型永久液泡，这两种结构不存在于动物细胞中。
3. 细胞分化（仅生物单科要求，卷2考察）★★★☆☆HL 专属⏱ 3 min
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细胞分化
未特化的干细胞改变自身结构与功能，逐步成为适配特定作用的特化细胞的过程。
分化对于复杂多细胞生物的发育至关重要：它让细胞形成执行特定功能的特化组织（例如肌肉、神经、叶栅栏组织），而非所有细胞都执行相同的通用功能。
解释细胞分化对人类胚胎发育的重要性。
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步骤1：定义分化：它是未特化的细胞逐步适配特定功能的过程。
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步骤2：联系胚胎发育相关知识：胚胎最初是一个受精卵细胞，该细胞必须发生分化，才能形成人体所需的所有特化细胞类型，例如神经细胞、肌肉细胞、血细胞。
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最终答案：细胞分化可让未特化的胚胎细胞发育为功能完整的人体所需的全部特化细胞类型，包括神经细胞、肌肉细胞和血细胞。
4. 医学中的干细胞（仅生物学卷2考查内容）★★★☆☆HL 专属⏱ 4 min
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干细胞
未发生特化的细胞，既可以分裂产生更多未特化的细胞，也可以分化为其他类型的特化细胞。
Advantages: Can differentiate into almost any cell type, so can be used to replace damaged or diseased cells (e.g. insulin-producing cells for diabetes, nerve cells for spinal cord injuries), can be used to test new drugs without testing on human patients, and can reduce the need for animal testing.
Disadvantages: Embryonic stem cells are taken from unused embryos from IVF treatment, which raises ethical objections as some people believe embryos have a right to life, risk of immune rejection if stem cells are not a genetic match for the patient, risk of stem cells dividing uncontrollably and forming tumours in the patient's body.
评价利用干细胞治疗脊髓损伤导致的瘫痪患者的应用方案。
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步骤1：陈述一项优点：干细胞可以分化为神经细胞，替代脊髓中受损的神经细胞，有望为没有其他治疗方案的患者恢复运动能力。
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步骤2：陈述一项缺点：如果使用胚胎干细胞，将胚胎用于医学治疗会存在伦理层面的争议。同时还存在新细胞被患者免疫系统排斥，或者形成肿瘤的风险。
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最终的全面结论：尽管干细胞疗法有希望治愈瘫痪，但伦理层面的顾虑和临床风险意味着它目前还不是一种可广泛应用的治疗手段。
5. 常见陷阱
错误做法:
Calling the cell membrane "semi-permeable" or "fully permeable"
原因:
Edexcel mark schemes only accept the term "partially permeable" for the cell membrane
正确做法:
Always use the exact phrase "partially permeable" when describing the cell membrane's function
错误做法:
Stating that animal cells have large permanent vacuoles
原因:
Animal cells only have small temporary vacuoles if any; large permanent vacuoles are unique to plant cells
正确做法:
When comparing plant and animal cells, explicitly state that plant cells have a large permanent vacuole while animal cells do not
错误做法:
Only describing advantages of stem cells when asked to evaluate their use
原因:
Evaluation questions require a balanced response covering both pros and cons to get full marks
正确做法:
Always include at least one advantage and one disadvantage of stem cell use in evaluation answers
错误做法:
Omitting ribosomes or vacuoles from lists of cell organelles
原因:
The specification requires you to know all 8 organelles, including ribosomes and vacuoles, which are commonly forgotten
正确做法:
Memorise the full list of 8 organelles: nucleus, cytoplasm, cell membrane, cell wall, mitochondria, chloroplasts, ribosomes, vacuole
错误做法:
Stating that cell walls are found in animal cells
原因:
Cell walls made of cellulose are only present in plant cells, not animal cells
正确做法:
When listing features of animal cells, explicitly exclude cell walls, chloroplasts and large permanent vacuoles
6. 速查表
Topic | Key Exam Facts |
|---|---|
Organelle Functions | Nucleus=controls cell; Mitochondria=respiration; Chloroplasts=photosynthesis; Ribosomes=protein synthesis; Cell membrane=partially permeable; Cell wall=cellulose support; Vacuole=cell sap/turgor; Cytoplasm=reaction site |
Plant vs Animal Cells | Shared: nucleus, cytoplasm, cell membrane, mitochondria, ribosomes. Plant only: cell wall, chloroplasts, large permanent vacuole |
Cell Differentiation (B only) | Process where stem cells become specialised; essential for multicellular organism development |
Stem Cells (B only) | Advantages: treat disease, replace damaged cells. Disadvantages: ethical objections (embryos), rejection risk, tumour risk |
7. 常见问题
细胞膜是半透性还是部分可透性的？
在Edexcel IGCSE生物考试中，描述细胞膜时必须使用“部分可透性”这一术语。官方评分标准不接受“半透性”的表述。
植物细胞有哪些独有的特征？
植物细胞拥有三种动物细胞不具备的特征：1. 纤维素细胞壁，2. 叶绿体，3. 大型永久液泡（动物细胞即使存在液泡，也仅为小型临时液泡）。
我需要为卷1复习干细胞相关内容吗？
不需要：单科生物考生仅在卷2（4BI1/2B）中考察2.5B（细胞分化）和2.6B（干细胞）的知识点。双证书考生不需要复习这些主题。
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下一步
Now that you have mastered cell structure, you are ready to move on to studying the organisation of cells into tissues, organs and organ systems, which builds on your knowledge of specialised cell function. You will also explore how substances move across cell membranes via diffusion, osmosis and active transport, which relies on your understanding of the partially permeable cell membrane. For Paper 2 Biology students, your next step is to learn about specialised cell adaptations, which links directly to the cell differentiation content covered in this guide. Make sure you practice past paper questions on cell structure to familiarise yourself with mark scheme expectations.