WJEC GCSE Biology: Cells 考点全突破

WJEC GCSE Biology: Cells 考点全突破

Cells are the building blocks of all life. In the WJEC GCSE Biology specification, "Cells and Movement Across Membranes" is one of the most heavily examined units. Mastering cell structure, organelle functions, and transport mechanisms is essential for Paper 1 and Paper 2 success. 细胞是所有生命的基本单位。WJEC GCSE 生物考纲中"细胞与跨膜运输"是考查密度最高的单元之一。掌握细胞结构和运输机制是冲刺高分的关键。

1. Animal and Plant Cells 动植物细胞

Shared organelles: nucleus (controls cell, contains DNA), cytoplasm (metabolic reactions), cell membrane (selectively permeable), mitochondria (aerobic respiration), ribosomes (protein synthesis). 共有细胞器：细胞核（含DNA）、细胞质（代谢）、细胞膜（选择性渗透）、线粒体（有氧呼吸）、核糖体（蛋白质合成）。

Plant cells also have: cell wall (cellulose, structural support), large vacuole (cell sap, turgor), chloroplasts (photosynthesis, chlorophyll). 植物细胞独有：纤维素细胞壁、大型液泡（膨压）、叶绿体（光合作用）。

Exam Tip: WJEC "compare and contrast" questions require both similarities AND differences. Memorise three plant-only structures: cell wall, vacuole, chloroplasts. 考点提示：对比题需同时列出相同点和不同点。

2. Specialised Cells 特化细胞

Sperm cells: acrosome (enzymes to penetrate egg), many mitochondria (energy), flagellum (movement). 精子：顶体含酶穿透卵子，大量线粒体供能，鞭毛运动。

Root hair cells: long extension (large surface area for absorption), no chloroplasts. 根毛细胞：长突起增大吸收面积，无叶绿体。

Xylem vessels: dead cells, lignin-reinforced walls, hollow tubes, no cytoplasm. 木质部：死细胞，木质素加固，中空管道，无细胞质。

Red blood cells: biconcave shape (large surface area), no nucleus (more haemoglobin space). 红细胞：双凹圆盘状，无核最大化血红蛋白空间。

3. Prokaryotic vs Eukaryotic 原核与真核

Eukaryotic (plants, animals, fungi): true nucleus, membrane-bound organelles, linear DNA. 真核：真正细胞核，膜结合细胞器，线性DNA。

Prokaryotic (bacteria): no nucleus, single circular DNA, plasmids, much smaller (1-5 um). 原核：无核，单环状DNA，含质粒，远小于真核细胞。

Common mistake: bacterial cell walls are made of peptidoglycan, NOT cellulose. 常见错误：细菌细胞壁成分为肽聚糖而非纤维素。

4. Diffusion, Osmosis and Active Transport 运输机制

Diffusion: net movement from high to low concentration, passive, no energy. E.g. oxygen into blood at alveoli. 扩散：高浓度向低浓度净移动，被动，无需能量。如肺泡中氧气入血。

Osmosis: water diffusion through a partially permeable membrane from dilute to concentrated solution. 渗透：水通过半透膜从稀溶液向浓溶液扩散。

Active transport: against concentration gradient, requires ATP and carrier proteins. E.g. mineral ions into root hairs. 主动运输：逆浓度梯度，需ATP和载体蛋白。如矿质离子进入根毛。

Key practical: potato cylinders in sucrose solutions — investigate osmosis. Know IV (concentration), DV (mass change), and explain hypotonic/isotonic/hypertonic. 必考实验：土豆条蔗糖溶液渗透实验，掌握自变量和因变量。

5. Microscopy and Magnification 显微镜与倍数

Formula: Magnification = Image size / Actual size. 公式：放大倍数 = 图像尺寸 / 实际尺寸。Unit conversions: 1 mm = 1000 um, 1 um = 1000 nm. Light microscope: max ~x1500, resolves ~0.2 um. Electron microscope: resolves ~0.2 nm, reveals organelle details. 光镜约x1500，分辨率0.2 um；电镜分辨率0.2 nm。

6. Mitosis and Organisation 有丝分裂与组织层次

Mitosis: produces two genetically identical cells for growth and repair. Stages: DNA replicates, chromosomes line up at equator, copies separate to poles, cytoplasm divides. 有丝分裂产生两个基因相同的子细胞。过程：DNA复制、染色体排列赤道板、分离至两极、细胞质分裂。

Organisation: Cells - Tissues - Organs - Organ Systems - Organism. Tissue = group of similar cells. Organ = different tissues working together. 组织层次：细胞-组织-器官-器官系统-生物体。

Don't confuse mitosis (2 identical diploid cells) with meiosis (4 different haploid gametes). Meiosis is in "Variation and Evolution", not Cells unit. 别混淆有丝分裂和减数分裂。

7. Exam Strategy 备考策略

Command words: "State" = brief answer; "Describe" = what happens; "Explain" = how and why with reasoning. 指令词：State简答，Describe描述过程，Explain科学原理。

6-mark QER: structure as point-evidence-explanation. Common topics: compare plant vs animal cells, osmosis practical, specialised cell adaptations. 6分扩展题结构：观点-证据-解释。

Revision tips: draw labelled cell diagrams from memory, practise magnification calculations with unit conversions, complete past paper osmosis questions, make organelle function flashcards. 复习建议：默画标注图，练习倍数计算，完成历年渗透真题，制作功能闪卡。

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