A-Level OCR Biology: Last-Minute Revision Notes | A-Level OCR 生物：考前冲刺笔记

📚 A-Level OCR Biology: Last-Minute Revision Notes | A-Level OCR 生物：考前冲刺笔记

These concise revision notes are designed for last-minute preparation before the OCR A-Level Biology exam. They highlight the most commonly tested concepts, key definitions, and essential diagrams to ensure you are ready to tackle both multiple-choice and extended-response questions.

这套简洁的复习笔记专为OCR A-Level生物考前冲刺设计。突出最常考查的概念、关键定义和必会图表，帮助你应对选择题和简答题。

1. Cell Structure and Microscopy | 细胞结构与显微镜

Eukaryotic cells possess a true nucleus and membrane-bound organelles (mitochondria, ER, Golgi, lysosomes, chloroplasts in plants). Organelles have specific functions: mitochondria for ATP production, ribosomes for protein synthesis, RER for protein folding and transport.

真核细胞具有真正的细胞核和膜结合细胞器（线粒体、内质网、高尔基体、溶酶体，植物还有叶绿体）。细胞器有特定功能：线粒体产生ATP，核糖体合成蛋白质，粗面内质网进行蛋白质折叠与运输。

Prokaryotic cells are smaller, lack a nucleus, and contain circular DNA, plasmids, 70S ribosomes, and may have a capsule and flagella. Unlike eukaryotes, they divide by binary fission.

原核细胞较小，无细胞核，含有环状DNA、质粒、70S核糖体，并可能有荚膜和鞭毛。与真核细胞不同，它们通过二分裂方式增殖。

Magnification = Image size ÷ Actual size. Resolution is the ability to distinguish two close points; electron microscopes have much higher resolution than light microscopes. TEM shows internal detail, SEM surface.

放大倍数 = 图像大小 ÷ 实际大小。分辨率是分辨两个相近点的能力；电子显微镜的分辨率远高于光学显微镜。透射电镜显示内部细节，扫描电镜显示表面结构。

2. Biological Molecules: Carbohydrates and Lipids | 生物分子：碳水化合物与脂质

Monosaccharides (e.g., glucose, C₆H₁₂O₆) are the monomers. α-glucose and β-glucose differ in the orientation of the -OH group on carbon 1. Disaccharides form by condensation: maltose (α-glucose + α-glucose), sucrose (α-glucose + fructose).

单糖（如葡萄糖，C₆H₁₂O₆）是基本单位。α-葡萄糖与β-葡萄糖在1号碳上-OH方向不同。双糖通过缩合反应形成：麦芽糖（α-葡萄糖+α-葡萄糖）、蔗糖（α-葡萄糖+果糖）。

Polysaccharides: Starch (amylose + amylopectin) – energy store in plants, helical, compact. Glycogen – highly branched animal storage. Cellulose – β-glucose chains with hydrogen bonds forming strong microfibrils for cell walls.

多糖：淀粉（直链淀粉与支链淀粉）– 植物储能，螺旋状，致密。糖原 – 高度分支的动物储能。纤维素 – β-葡萄糖链通过氢键形成强韧微纤维，构成细胞壁。

Lipids: Triglycerides are esters of glycerol and three fatty acids; saturated fatty acids have no double bonds, unsaturated have one or more (cis/trans). Phospholipids have a hydrophilic phosphate head and hydrophobic tails, forming bilayers in membranes.

脂质：甘油三酯是甘油与三个脂肪酸形成的酯；饱和脂肪酸无双键，不饱和脂肪酸含一个或多个双键（顺式/反式）。磷脂具有亲水性磷酸头与疏水尾，能在膜中形成双层。

3. Proteins and Enzymes | 蛋白质与酶

Proteins are polymers of amino acids. Each amino acid has an amine group, carboxyl group, and a variable R group. Primary structure is the sequence, secondary α-helix and β-pleated sheet held by hydrogen bonds, tertiary 3D folding (ionic, hydrogen, disulfide bonds, hydrophobic interactions), quaternary involves multiple polypeptides.

蛋白质是氨基酸的多聚体。每个氨基酸含有一个氨基、一个羧基和一个可变的R基。一级结构为序列，二级为α-螺旋和β-折叠并由氢键维持，三级为三维折叠（离子键、氢键、二硫键、疏水相互作用），四级涉及多条多肽链。

Enzymes lower activation energy. Lock-and-key model: active site complementary to substrate. Induced fit: active site changes shape to bind substrate more closely. Factors affecting rate:

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