A-Level OCR Biology: End-of-Term Revision Guide | A-Level OCR 生物：期末复习提纲

📚 A-Level OCR Biology: End-of-Term Revision Guide | A-Level OCR 生物：期末复习提纲

Effective revision for A-Level OCR Biology requires a structured approach that connects theoretical concepts with practical skills. This guide summarises the core content across all modules, highlighting the essential knowledge and exam tips to help you consolidate your understanding before the end-of-term assessments.

高效的A-Level OCR生物复习需要将理论概念与实践技能相结合。本提纲汇总各模块的核心内容，突出关键知识点与应试技巧，帮助你在期末评估前巩固理解。

1. Cell Structure & Microscopy | 细胞结构与显微技术

All living organisms are composed of cells, which can be prokaryotic or eukaryotic. Prokaryotic cells, such as bacteria, lack a membrane-bound nucleus and organelles; their DNA is circular and free in the cytoplasm. Eukaryotic cells (animal, plant, fungal) possess a true nucleus and membrane-bound organelles including mitochondria, endoplasmic reticulum, Golgi apparatus, and in plants, chloroplasts and a large permanent vacuole. You must be able to recognise and label organelles from electron micrographs and diagrams.

所有生物体由细胞构成，分为原核细胞和真核细胞。原核细胞（如细菌）没有膜包被的细胞核和细胞器，其DNA呈环状游离在细胞质中。真核细胞（动物、植物、真菌）具有真正的细胞核和膜包被的细胞器，包括线粒体、内质网、高尔基体；植物细胞还含有叶绿体和中央大液泡。你必须能从电子显微照片和示意图中识别并标注这些细胞器。

Magnification and resolution are fundamental. Magnification = image size ÷ actual size. Always calibrate the eyepiece graticule using a stage micrometer before measuring objects under a light microscope. Remember that electron microscopes use a beam of electrons and offer much higher resolution, but they cannot be used with living specimens and require extensive preparation.

放大倍数和分辨率是基础概念。放大倍数 = 图像大小 ÷ 实际大小。使用光学显微镜测量前，务必用镜台测微尺校准目镜测微尺。记住电子显微镜利用电子束，分辨率高得多，但不能观察活体样本且需要复杂的样品制备。

Feature	Light microscope	Transmission EM (TEM)	Scanning EM (SEM)
Radiation used	Visible light	Electrons	Electrons
Maximum resolution	~200 nm	~0.1 nm	~0.1 nm
Image produced	2D (can be coloured)	2D cross-section	3D surface
Sample condition	Living or dead	Dead, stained, in vacuum	Dead, coated, in vacuum

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2. Biological Molecules | 生物分子

Water is a polar molecule that forms hydrogen bonds, giving it key properties such as high specific heat capacity, cohesion, adhesion, and excellent solvent capacity. These properties make water essential for life: it acts as a transport medium, coolant, and habitat.

水是极性分子，能形成氢键，赋予了它高比热容、内聚力、附着力和优良的溶剂能力等关键性质。这些性质使水成为生命不可或缺的物质：作为运输介质、冷却剂和栖息地。

Carbohydrates range from monosaccharides (e.g. glucose, fructose) to disaccharides (maltose, sucrose, lactose) and polysaccharides (starch, glycogen, cellulose). Starch (amylose and amylopectin) is the main storage carbohydrate in plants, while glycogen is the animal equivalent. Cellulose is a structural polysaccharide composed of β-glucose linked by 1,4-glycosidic bonds, forming straight chains cross-linked by hydrogen bonds.

碳水化合物从单糖（如葡萄糖、果糖）到二糖（麦芽糖、蔗糖、乳糖）和多糖（淀粉、糖原、纤维素）。淀粉（直链淀粉和支链淀粉）是植物主要的储存多糖，糖原是动物的对应物。纤维素是由β-葡萄糖通过1,4-糖苷键连接而成的结构多糖，形成由氢键交联的直链。

Lipids include triglycerides, phospholipids and cholesterol. Triglycerides are formed by esterification of one glycerol and three fatty acids; they are used for energy storage. Phospholipids have a phosphate head (hydrophilic) and two fatty acid tails (hydrophobic), allowing them to form bilayers in water – the basis of cell membranes.

脂质包括甘油三酯、磷脂和胆固醇。甘油三酯由一个甘油和三个脂肪酸通过酯化反应形成，用于能量储存。磷脂具有一个亲水磷酸头和一个疏水双脂肪酸尾，使其在水中形成双分子层，这是细胞膜的基础。

Proteins are polymers of amino acids joined by peptide bonds. The four levels of structure – primary, secondary (α-helix, β-pleated sheet), tertiary and quaternary – determine a protein’s specific function. The tertiary structure is stabilised by hydrogen bonds, ionic bonds, hydrophobic interactions and disulfide bridges. Collagen and haemoglobin are key examples of quaternary structure.

蛋白质是由氨基酸通过肽键连接而成的多聚体。四个结构层次——一级、二级（α-螺旋、β-折叠）、三级和四级——决定了蛋白质的特定功能。三级结构由氢键、离子键、疏水相互作用和二硫键稳定。胶原蛋白和血红蛋白是四级结构的关键例子。

Nucleic acids DNA and RNA store and transmit genetic information. DNA is a double helix of deoxyribonucleotides with bases adenine, thymine, cytosine and guanine. RNA is single-stranded and contains uracil instead of thymine. The double helix is held together by complementary base pairing (A-T, C-G) via hydrogen bonds.

核酸DNA和RNA储存并传递遗传信息。DNA是由脱氧核糖核苷酸组成的双螺旋，含腺嘌呤、胸腺嘧啶、胞嘧啶和鸟嘌呤碱基。RNA为单链，含尿嘧啶而非胸腺嘧啶。双螺旋通过互补碱基配对（A-T、C-G）所产生的氢键维持。

The biochemical tests for key molecules must be memorised: reducing sugars with Benedict’s solution (heat, red precipitate), non-reducing sugars after acid hydrolysis, starch with iodine (blue-black), proteins with biuret reagent (purple), lipids with the emulsion test (cloudy white).

必须熟记关键分子的生化检验：还原糖用本尼迪克特试剂（加热，产生红色沉淀），非还原糖经酸水解后测定，淀粉遇碘变蓝黑色，蛋白质与双缩脲试剂呈紫色，脂质通过乳浊试验产生乳白色。

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3. Enzymes | 酶

Enzymes are biological catalysts that lower activation energy. The induced-fit model describes how the active site changes shape slightly as the substrate binds, putting strain on bonds to facilitate the reaction. Enzyme kinetics are affected by temperature (optimum, denaturation), pH (affects ionic bonds in the active site), substrate concentration (saturation) and enzyme concentration.

酶是能降低活化能的生物催化剂。诱导契合模型描述了底物结合时活性部位形状发生轻微改变，对化学键施加压力以促进反应。酶动力学受温度（最适温度、变性）、pH（影响活性部位的离子键）、底物浓度（达到饱和）和酶浓度的影响。

Competitive inhibitors resemble the substrate and bind reversibly to the active site, competing with the substrate. Non-competitive inhibitors bind to an allosteric site, changing the shape of the active site so substrate cannot bind. Increasing substrate concentration overcomes competitive inhibition but has no effect on non-competitive inhibition.

竞争性抑制剂与底物结构相似，可逆地与活性位点结合，从而与底物竞争。非竞争性抑制剂结合在别构部位，改变活性位点的形状，使底物无法结合。增加底物浓度可以克服竞争性抑制，但对非竞争性抑制剂无效。

Cofactors and coenzymes are non-protein helpers required for some enzymes to function. Many coenzymes are derived from vitamins. For instance, NAD⁺ and FAD are coenzymes crucial in respiration. Immobilised enzymes are widely used in industry (e.g. lactose-free milk) because they can be reused and are more stable.

辅因子和辅酶是一些酶发挥作用所需的非蛋白质助手。许多辅酶来源于维生素。例如，NAD⁺和FAD是呼吸作用中关键的辅酶。固定化酶因可重复使用且稳定性更高而被广泛用于工业（如无乳糖牛奶）。

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4. Cell Membranes & Transport | 细胞膜与运输

The fluid mosaic model describes the cell membrane as a phospholipid bilayer with embedded proteins, cholesterol (in animal cells) and glycoproteins. The ‘fluid’ refers to the movement of phospholipids, and ‘mosaic’ to the scattered proteins. Channel and carrier proteins facilitate the transport of specific molecules.

流动镶嵌模型将细胞膜描述为磷脂双分子层，其中嵌有蛋白质、胆固醇（动物细胞）和糖蛋白。”流动”指磷脂可以移动，”镶嵌”指蛋白质散在分布。通道蛋白和载体蛋白促进特定分子的运输。

Passive transport includes simple diffusion and facilitated diffusion (through channel or carrier proteins), both down a concentration gradient with no ATP required. Osmosis is the net movement of water molecules through a selectively permeable membrane from a region of higher water potential (less negative) to a region of lower water potential (more negative). Water potential is measured in kPa and is the sum of solute potential and pressure potential: Ψ = Ψₚ + Ψₙ.

被动运输包括简单扩散和借助通道蛋白或载体蛋白的易化扩散，两者均顺浓度梯度进行，不消耗ATP。渗透是水分子通过选择渗透膜从较高水势（较不负值）区域向较低水势（较更负值）区域的净移动。水势以kPa为单位，为溶质势和压力势之和。

Active transport uses carrier proteins and ATP to move molecules against a concentration gradient, e.g. the sodium–potassium pump. Bulk transport involves endocytosis (phagocytosis for solids, pinocytosis for liquids) and exocytosis, requiring energy and membrane remodelling.

主动运输利用载体蛋白和ATP逆浓度梯度移动分子，例如钠钾泵。胞吞（固体颗粒为吞噬，液体为胞饮）和胞吐属于批量运输，需要能量并涉及膜的重新构建。

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5. Cell Division & Cellular Organisation | 细胞分裂与细胞组织

The cell cycle consists of interphase (G₁, S, G₂) and the mitotic phase. During S phase, DNA is replicated to form sister chromatids held together at the centromere. Mitosis comprises prophase, metaphase, anaphase and telophase, followed by cytokinesis. Mitosis produces two genetically identical diploid daughter cells and is essential for growth, repair and asexual reproduction.

细胞周期包括间期（G₁、S、G₂）和有丝分裂期。S期DNA复制形成由着丝粒连接在一起的姐妹染色单体。有丝分裂包括前期、中期、后期和末期，随后进行胞质分裂。有丝分裂产生两个遗传上完全相同的二倍体子细胞，对生长、修复和无性繁殖至关重要。

Meiosis produces four genetically unique haploid gametes through two consecutive divisions. Homologous chromosomes pair up (synapsis) in prophase I, and crossing over exchanges genetic material between chromatids, increasing variation. Independent assortment of chromosomes during metaphase I further shuffles alleles. Gametes fuse at fertilisation to restore the diploid number.

减数分裂通过连续两次分裂产生四个遗传上独特的单倍体配子。同源染色体在前期I配对（联会），交叉互换在染色单体间交换遗传物质，增加变异。中期I染色体的独立分配进一步重组等位基因。配子在受精时融合，恢复二倍体数。

Stem cells are unspecialised cells that can divide and differentiate. Embryonic stem cells are totipotent (can become any cell type) while adult stem cells are multipotent (limited range). The use of stem cells in medicine raises ethical issues. Stem cell niches in adults, such as bone marrow, are a focus of therapies.

干细胞是可分裂和分化的未特化细胞。胚胎干细胞为全能性（可发育成任何细胞类型），成体干细胞为多能性（范围有限）。干细胞在医学中的应用引发了伦理问题。成体中的干细胞龛（如骨髓）是疗法的重点。

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6. Exchange Surfaces & Gas Exchange | 交换表面与气体交换

All organisms must exchange materials with their environment. Key features of effective exchange surfaces are a large surface area, thin surface, steep concentration gradient maintained and, in animals, a rich blood supply. The mammalian gas exchange system includes the trachea, bronchi, bronchioles and alveoli. Surfactants in the alveoli reduce surface tension preventing collapse.

所有生物都必须与环境进行物质交换。高效交换表面的关键特征是：表面积大、厚度薄、维持陡峭的浓度梯度，在动物中还需有丰富的血液供应。哺乳动物气体交换系统包括气管、支气管、细支气管和肺泡。肺泡中的表面活性物质降低表面张力，防止塌陷。

Ventilation involves inspiration (diaphragm contracts and flattens, external intercostal muscles contract, thorax volume increases, pressure drops) and expiration (mostly passive at rest). The tidal volume, vital capacity and ventilation rate can be measured using a spirometer.

通气包括吸气（膈肌收缩变平，外肋间肌收缩，胸廓容积增大，压力下降）和呼气（静息时主要被动）。潮气量、肺活量和通气频率可用肺活量计测量。

In fish, oxygen is extracted from water via the countercurrent exchange system in the gill filaments, where blood flows in the opposite direction to water, maintaining a constant concentration gradient. Insect tracheae deliver air directly to tissues, with spiracles controlling water loss.

鱼类通过鳃丝的逆流交换系统从水中获取氧气，血液与水流方向相反，保持了恒定的浓度梯度。昆虫的气管直接将空气输送至组织，气门控制水分流失。

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7. Transport in Animals | 动物体内运输

The human circulatory system is a closed, double circulation. The heart has four chambers: right atrium, right ventricle, left atrium, left ventricle. Deoxygenated blood is pumped to the lungs (pulmonary circulation) and oxygenated blood to the body (systemic circulation). The sinoatrial node (SAN) initiates the heartbeat; the atrioventricular node (AVN) and Purkyne fibres coordinate contraction.

人体循环系统为封闭式、双循环。心脏有四个腔室：右心房、右心室、左心房、左心室。缺氧血泵向肺部（肺循环），富氧血泵向全身（体循环）。窦房结（SAN）发起心跳；房室结（AVN）和浦肯野纤维协调收收。

Haemoglobin has a quaternary structure with four polypeptide chains, each containing a haem group. The oxygen dissociation curve is S-shaped (sigmoidal) because cooperative binding makes it progressively easier for subsequent O₂ molecules to bind. The Bohr effect shifts the curve to the right in response to increased CO₂, lowering the pH and promoting oxygen unloading in respiring tissues.

血红蛋白具有四级结构，含四条多肽链，每条链有一个血红素基团。氧解离曲线呈S型是因为协同结合使后续氧分子更容易结合。玻尔效应使得CO₂增加时曲线右移，pH下降，促进呼吸组织中的氧气卸载。

Carbon dioxide is transported in the blood as hydrogencarbonate ions (HCO₃⁻), dissolved CO₂ and carbamino compounds. Tissue fluid is formed by ultrafiltration from blood capillaries, driven by hydrostatic pressure. Lymphatic vessels

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