📚 AS Cambridge Biology: Full Syllabus Breakdown | AS剑桥生物：课程大纲全面解析
Cambridge International AS Level Biology (9700) provides students with a solid foundation in the key principles of modern biology, covering everything from the microscopic world of cells to the macroscopic view of organ systems in living organisms. This syllabus breakdown outlines every major topic you will encounter, helping you plan an effective revision strategy and understand exactly what examiners expect.
剑桥国际AS Level生物课程（9700）为学生奠定现代生物学核心原理的坚实基础，内容涵盖从微观细胞世界到宏观生物体器官系统的方方面面。本次课程大纲解析将梳理你将会遇到的每一个重要主题，帮助你规划高效的复习策略，并准确理解考官的期望。
1. Cell Structure | 细胞结构
The study of life begins with the cell theory, which states that all organisms are composed of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells. Understanding the ultrastructure of prokaryotic and eukaryotic cells using electron micrographs is essential.
对生命的研究从细胞学说开始，该学说指出所有生物体都由细胞构成，细胞是生命的基本单位，并且所有细胞都来源于已有的细胞。利用电子显微照片理解原核细胞和真核细胞的超微结构是至关重要的。
Eukaryotic cells contain membrane-bound organelles such as the nucleus, mitochondria, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, and – in plants – chloroplasts and a large permanent vacuole. The functions of each organelle are directly linked to their structures; for instance, the extensive cristae of mitochondria provide a large surface area for oxidative phosphorylation.
真核细胞含有由膜包被的细胞器，如细胞核、线粒体、内质网、高尔基体、溶酶体，而植物细胞还含有叶绿体和一个大中央液泡。每种细胞器的功能都与其结构直接相关；例如，线粒体丰富的嵴为氧化磷酸化提供了巨大的表面积。
Prokaryotic cells, such as bacteria, lack a true nucleus and membrane-bound organelles. Their DNA lies free in the cytoplasm as a circular chromosome, and many have small loops of DNA called plasmids. Ribosomes are 70S in prokaryotes, compared to the 80S found in eukaryotic cytoplasm.
原核细胞（如细菌）缺少真正的细胞核和膜包裹的细胞器。它们的DNA以环状染色体的形式游离在细胞质中，许多还具有称为质粒的小型DNA环。原核生物的核糖体为70S型，而真核细胞质中的核糖体为80S型。
gnification = Image size ÷ Actual size, converting between millimetres (mm), micrometres (µm) and nanometres (nm).
根据图像计算放大倍数和实际尺寸是一项关键技能。学生必须自信地使用公式：放大倍数 = 图像尺寸 ÷ 实际尺寸，并能在毫米（mm）、微米（µm）和纳米（nm）之间进行换算。
2. Biological Molecules | 生物分子
Living organisms rely on a small set of carbon-based macromolecules: carbohydrates, lipids, proteins and nucleic acids. Carbohydrates are composed of monosaccharides such as glucose (C₆H₁₂O₆), which can link through glycosidic bonds to form disaccharides (e.g. maltose, sucrose) and polysaccharides (e.g. starch, glycogen, cellulose).
生物体依赖少数几种碳基大分子：碳水化合物、脂质、蛋白质和核酸。碳水化合物由葡萄糖（C₆H₁₂O₆）等单糖组成，它们可以通过糖苷键连接形成二糖（如麦芽糖、蔗糖）和多糖（如淀粉、糖原、纤维素）。
Lipids – principally triglycerides – are formed from glycerol and three fatty acid chains via ester bonds. Their hydrophobic nature makes them ideal for energy storage, thermal insulation and as components of cell membranes (phospholipids).
脂质——主要是甘油三酯——由甘油和三条脂肪酸链通过酯键形成。它们的疏水性使其非常适合能量储存、隔热以及作为细胞膜的组分（磷脂）。
Proteins have four levels of structure. The primary structure is the sequence of amino acids joined by peptide bonds. Secondary structure arises from hydrogen bonding, forming α-helices and β-pleated sheets. Tertiary structure involves further folding due to disulfide bridges, ionic bonds and hydrophobic interactions, while quaternary structure refers to the association of multiple polypeptide chains, as in haemoglobin.
蛋白质具有四级结构。一级结构是由肽键连接的氨基酸序列。二级结构源于氢键作用，形成α-螺旋和β-折叠片层。三级结构通过二硫键、离子键和疏水相互作用进一步折叠，而四级结构则涉及多条多肽链的结合，如血红蛋白。
Water’s properties – high specific heat capacity, latent heat of vaporisation, cohesion and its role as a solvent – are indispensable for life. These properties arise from hydrogen bonding between polar water molecules.
水的特性——高比热容、高汽化潜热、内聚力以及作为溶剂的作用——对生命不可或缺。这些特性来源于极性水分子之间的氢键。
3. Enzymes | 酶
Enzymes are globular proteins that function as biological catalysts, lowering the activation energy of metabolic reactions. The lock-and-key and induced-fit models explain how a specific substrate binds to the enzyme’s active site. The induced-fit model highlights how the active site changes shape slightly to mould around the substrate.
酶是球状蛋白，作为生物催化剂发挥作用，降低代谢反应的活化能。锁钥模型和诱导契合模型解释了特定底物如何与酶的活性位点结合。诱导契合模型强调活性位点如何略微改变形状以包绕底物。
The rate of an enzyme-catalysed reaction is influenced by temperature, pH, enzyme concentration and substrate concentration. At low temperatures, kinetic energy is low; as temperature increases, rate rises until the enzyme denatures. Extreme pH values disrupt ionic and hydrogen bonds, altering the tertiary structure and denaturing the enzyme.
酶促反应的速率受温度、pH、酶浓度和底物浓度的影响。低温下动能较低；随着温度升高，反应速率加快，直至酶变性。极端的pH值会破坏离子键和氢键，改变三级结构并使酶变性。
The initial rate of reaction is determined from the gradient of the tangent at time zero on a progress curve. Vmax and Km are key kinetic parameters, though at AS level students focus on interpreting rate graphs and explaining the effects of competitive and non-competitive inhibition.
反应初速率由进程曲线上零时刻的切线斜率确定。Vmax 和 Km 是关键的动力学参数，但在AS阶段，学生重点在于解读速率曲线图并解释竞争性抑制和非竞争性抑制的影响。
4. Cell Membranes and 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' aspect arises because phospholipids and proteins can move laterally, while the 'mosaic' refers to the patchwork of different proteins.
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（动物细胞中）和糖蛋白。“流动”的一面源于磷脂和蛋白质可以横向移动，“镶嵌”则指由不同蛋白质组成的拼图式结构。
Movement across membranes includes diffusion, facilitated diffusion, osmosis and active transport. Diffusion is the net movement of particles down a concentration gradient. Facilitated diffusion uses channel or carrier proteins. Active transport requires energy from ATP to move substances against their gradient, e.g. the sodium‑potassium pump.
跨膜运输包括扩散、协助扩散、渗透和主动运输。扩散是粒子沿着浓度梯度的净移动。协助扩散利用通道蛋白或载体蛋白。主动运输需要ATP提供的能量，逆浓度梯度运输物质，例如钠-钾泵。
Endocytosis and exocytosis are bulk transport mechanisms requiring energy and involving the formation or fusion of vesicles with the plasma membrane. Osmosis, the diffusion of water through a selectively permeable membrane, is examined in terms of water potential (ψ), with water moving from a region of higher ψ to lower ψ.
胞吞和胞吐是需要能量的批量运输机制，涉及囊泡的形成或与细胞膜的融合。渗透是水通过选择性通透膜的扩散，以水势（ψ）来考查，水从较高水势的区域流向较低水势的区域。
5. The Mitotic Cell Cycle | 细胞周期与有丝分裂
The cell cycle consists of interphase (G₁, S and G₂ phases) and the mitotic phase. During interphase, DNA is replicated and the cell grows. Mitosis, the division of the nucleus, ensures genetically identical nuclei are produced for growth, repair and asexual reproduction.
细胞周期由间期（G₁期、S期和G₂期）和分裂期组成。在间期，DNA进行复制，细胞生长。有丝分裂即细胞核的分裂，确保产生遗传上完全相同的细胞核，用于生长、修复和无性生殖。
The stages of mitosis are prophase, metaphase, anaphase and telophase. In prophase, chromosomes condense and the nuclear envelope breaks down. During metaphase, chromosomes align at the equator. Anaphase separates sister chromatids, and telophase sees the reformation of nuclear envelopes. Cytokinesis follows, splitting the cytoplasm.
有丝分裂的阶段包括前期、中期、后期和末期。前期染色体凝集，核膜解体。中期染色体排列在赤道板上。后期姐妹染色单体分离，末期中核膜重新形成。随后进行胞质分裂，将细胞质分开。
Cancer results from uncontrolled cell division. Mutations in proto-oncogenes and tumour-suppressor genes can lead to the formation of tumours. Understanding the cell cycle has guided the development of some chemotherapy drugs that disrupt spindle fibre assembly.
癌症由不受控制的细胞分裂引起。原癌基因和抑癌基因的突变可导致肿瘤形成。对细胞周期的理解为一些干扰纺锤丝组装的化疗药物的开发提供了指导。
6. Nucleic Acids and Protein Synthesis | 核酸与蛋白质合成
DNA is a double-stranded polynucleotide composed of deoxyribonucleotides. Each nucleotide contains a phosphate group, a deoxyribose sugar and a nitrogenous base (adenine, thymine, cytosine or guanine). Two strands run antiparallel and are held together by hydrogen bonds between complementary base pairs A–T and C–G.
DNA是双链多核苷酸，由脱氧核糖核苷酸组成。每个核苷酸含有一个磷酸基团、一个脱氧核糖和一个含氮碱基（腺嘌呤、胸腺嘧啶、胞嘧啶或鸟嘌呤）。两条链反向平行，并通过互补碱基对A–T和C–G之间的氢键连接。
RNA is single-stranded and contains ribose instead of deoxyribose, with uracil replacing thymine. Messenger RNA (mRNA) carries the genetic code from DNA to ribosomes. Transcription produces a complementary mRNA strand, and translation uses transfer RNA (tRNA) to assemble amino acids into a polypeptide.
RNA是单链结构，含有核糖而非脱氧核糖，尿嘧啶取代了胸腺嘧啶。信使RNA（mRNA）将遗传密码从DNA携带到核糖体。转录产生互补的mRNA链，翻译则利用转运RNA（tRNA）将氨基酸组装成多肽。
The genetic code is degenerate, meaning most amino acids are encoded by more than one codon. Students analyse sequences and predict amino acid sequences using a codon table. Gene mutations such as base substitutions, insertions and deletions can alter the polypeptide product, sometimes with harmful effects.
遗传密码具有简并性，即大多数氨基酸由不止一个密码子编码。学生需分析序列并使用密码子表预测氨基酸序列。基因突变，如碱基替换、插入和缺失，可能改变多肽产物，有时会造成有害影响。
7. Transport in Plants | 植物中的运输
Xylem vessels transport water and dissolved mineral ions from roots to leaves. The mechanism of transpiration pull – driven by evaporation from leaf mesophyll cells – creates tension that draws water up the xylem. Cohesion between water molecules and adhesion of water to xylem walls maintain the continuous water column.
木质部导管将水及溶解的矿质离子从根运输到叶。蒸腾拉力的机制——由叶肉细胞蒸发驱动——产生拉力，将水向上拉拽通过木质部。水分子之间的内聚力以及水与木质部壁的附着力维持了连续的水柱。
Phloem translocates sucrose and amino acids from sources (e.g. leaves) to sinks (e.g. roots, developing fruits) using an active process. The mass-flow hypothesis involves loading sucrose into sieve tubes at the source, decreasing water potential and drawing water in by osmosis, which increases pressure and drives flow towards the sink.
韧皮部利用主动过程将蔗糖和氨基酸从源（如叶片）转运到库（如根、发育中的果实）。集流假说涉及在源端将蔗糖载入筛管，降低水势并通过渗透作用吸入水分，这增加了压力并驱动水流向库端。
Investigating transport often involves using a potometer to measure transpiration rates, and ringing experiments that remove a ring of bark to demonstrate the role of phloem. Adaptations of xerophytes, such as sunken stomata and thick cuticles, reduce water loss.
研究运输常使用蒸腾计来测量蒸腾速率，以及环割实验（剥去一圈树皮）来证明韧皮部的作用。旱生植物的适应性特征，如凹陷的气孔和厚的角质层，可减少水分丧失。
8. Transport in Mammals | 哺乳动物的运输
The mammalian circulatory system is a closed, double circulation with a four-chambered heart. Deoxygenated blood returns to the right atrium, passes to the right ventricle and is pumped to the lungs. Oxygenated blood returns to the left atrium, enters the left ventricle and is pumped to the rest of the body.
哺乳动物的循环系统是封闭式的双循环系统，心脏有四个腔室。缺氧血返回右心房，进入右心室并被泵送到肺部。富氧血返回左心房，进入左心室并被泵送到全身各处。
The cardiac cycle includes atrial systole, ventricular systole and diastole. Valves prevent backflow, and the heartbeat is initiated by the sinoatrial node (SAN), which sends out electrical impulses causing atrial contraction. The atrioventricular node (AVN) passes the impulse to the ventricles after a slight delay.
心动周期包括心房收缩期、心室收缩期和舒张期。瓣膜防止血液倒流，心跳由窦房结（SAN）启动，它发出电脉冲引起心房收缩。房室结（AVN）在短暂的延迟后将冲动传至心室。
Blood consists of plasma, red blood cells (erythrocytes), white blood cells (leucocytes) and platelets. Haemoglobin in erythrocytes binds oxygen to form oxyhaemoglobin. The Bohr effect describes how increased carbon dioxide concentration decreases haemoglobin’s affinity for oxygen, enhancing oxygen delivery to respiring tissues.
血液由血浆、红细胞、白细胞和血小板组成。红细胞中的血红蛋白结合氧气形成氧合血红蛋白。玻尔效应描述了二氧化碳浓度升高如何降低血红蛋白对氧气的亲和力，从而促进氧气向呼吸组织的释放。
9. Gas Exchange | 气体交换
Effective gas-exchange surfaces are thin, moist, have a large surface area and are highly vascularised. The mammalian lung contains millions of alveoli, each surrounded by a dense capillary network. Oxygen diffuses from alveolar air into blood, while carbon dioxide diffuses in the opposite direction.
高效的气体交换面薄而湿润、表面积大且血管丰富。哺乳动物的肺含有数百万个肺泡，每个肺泡被密集的毛细血管网包围。氧气从肺泡气扩散进入血液，二氧化碳则沿相反方向扩散。
The trachea, bronchi and bronchioles form the airway system. Cartilage rings keep airways open, smooth muscle allows constriction and dilation, and goblet cells secrete mucus to trap pathogens. Ciliated epithelium wafts mucus upwards, protecting the lungs.
气管、支气管和细支气管构成气道系统。软骨环保持气道通畅，平滑肌允许收缩和舒张，杯状细胞分泌黏液以捕获病原体。纤毛上皮将黏液向上推，保护肺部。
Smoking damages the gas-exchange system. Tar paralyses cilia, chronic bronchitis inflames airways, and emphysema destroys alveolar walls, reducing surface area. These effects reduce efficiency of gas exchange and can lead to diseases such as chronic obstructive pulmonary disease (COPD).
吸烟损害气体交换系统。焦油使纤毛麻痹，慢性支气管炎引起气道发炎，肺气肿则破坏肺泡壁，减少表面积。这些影响降低了气体交换的效率，并可导致慢性阻塞性肺病（COPD）。
10. Infectious Diseases | 传染病
Infectious diseases are caused by pathogens: bacteria, viruses, fungi and protists. Transmission can be direct (contact, droplet infection) or indirect (vectors, contaminated food or water). Cholera, caused by the bacterium Vibrio cholerae, is transmitted through faecally contaminated water and causes severe diarrhoea.
传染病由病原体引起：细菌、病毒、真菌和原生生物。传播途径可以是直接传播（接触、飞沫感染）或间接传播（媒介、受污染的食物或水）。霍乱由霍乱弧菌引起，通过被粪便污染的水传播，导致严重腹泻。
Malaria is caused by Plasmodium protists and transmitted by female Anopheles mosquitoes. The parasite multiplies in liver cells and red blood cells, causing cycles of fever. Tuberculosis (TB), caused by Mycobacterium tuberculosis, spreads through airborne droplets when infected individuals cough or sneeze.
疟疾由疟原虫引起，通过雌性按蚊传播。这种寄生虫在肝细胞和红细胞中繁殖，引起周期性的发热。结核病（TB）由结核分枝杆菌引起，当感染者咳嗽或打喷嚏时通过空气飞沫传播。
Antibiotics such as penicillin target bacterial cell wall synthesis but are ineffective against viruses. Overuse leads to antibiotic resistance via natural selection, where resistant bacteria survive and pass on resistance genes. This has become a major global health concern.
青霉素等抗生素以细菌细胞壁合成为靶点，但对病毒无效。滥用抗生素会通过自然选择导致抗生素耐药性，耐药细菌存活下来并将抗性基因传递下去。这已成为全球性的重大健康问题。
11. Immunity | 免疫
The immune system distinguishes 'self' from 'non-self' using antigens. Phagocytes like neutrophils and macrophages carry out non-specific phagocytosis, engulfing and destroying pathogens. Inflammation and the release of histamine increase blood flow to infected areas.
免疫系统利用抗原来区分“自身”和“非自身”。中性粒细胞和巨噬细胞等吞噬细胞进行非特异性吞噬作用，吞噬并消灭病原体。炎症和组胺的释放增加流向感染区域的血液。
Specific immune responses involve T-lymphocytes and B-lymphocytes. Helper T-cells activate B-cells to divide and differentiate into plasma cells and memory cells. Plasma cells secrete antibodies that opsonise pathogens, neutralise toxins or agglutinate cells. Memory cells ensure a rapid and strong secondary response upon re-infection.
特异性免疫反应涉及T淋巴细胞和B淋巴细胞。辅助性T细胞激活B细胞，使其分裂并分化为浆细胞和记忆细胞。浆细胞分泌抗体，这些抗体可调理病原体、中和毒素或使细胞凝集。记忆细胞确保再次感染时能产生快速而强烈的二次免疫应答。
Vaccination introduces antigens to trigger an immune response without causing disease, leading to the production of memory cells. Herd immunity protects unvaccinated individuals when a high percentage of the population is immune. Active and passive immunity differ in their origin (natural vs. artificial) and duration.
疫苗接种引入抗原以激发免疫应答而不引起疾病，导致记忆细胞的产生。当人群中高比例个体具有免疫力时，群体免疫可以保护未接种者。主动免疫和被动免疫在来源（自然或人工）和持续时间上有所不同。
12. Practical Skills and Assessment | 实验技能与评估
Paper 3 of the AS examination assesses practical skills. Students must be able to plan experiments, identify variables, and record observations in appropriate tables. Accurate drawing and labelling of specimens observed under a microscope is often tested.
AS考试的试卷三评估实验技能。学生必须能够设计实验、识别变量，并用合适的表格记录观察结果。常考核在显微镜下观察标本的精确绘图和标注。
Common investigations include tests for reducing and non-reducing sugars using Benedict’s solution, the biuret test for proteins, the emulsion test for lipids, and the use of iodine solution for starch. Quantitative skills, such as constructing dilution series and using colorimetry, may be required.
常见的考查内容包括利用本尼迪克特试剂检测还原糖和非还原糖、双缩脲法检测蛋白质、乳剂试验检测脂质以及碘液检测淀粉。定量技能，如构建稀释系列和使用比色法，也可能被要求掌握。
Evaluating data is crucial: students should comment on accuracy, reliability and limitations, and suggest improvements. Understanding the principles of safe laboratory practice, risk assessments and how to handle ethical issues when using living organisms are also essential.
数据评估至关重要：学生应评价准确度、可靠性和局限性，并提出改进建议。理解实验室安全规范的原则、风险评估以及使用活体生物时的伦理问题处理方式也同样重要。
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