📚 Introduction to A-Level Biology | A-Level 生物入门
A Level Biology is more than a collection of facts to memorise. It is a demanding, two-year course that asks you to explain how living systems work, to analyse experimental data, and to apply biological concepts to unfamiliar contexts. This introduction sets out the structure of Cambridge International AS and A Level Biology (9700), the key themes you will meet, and the skills you need to succeed.
A Level 生物不仅仅是一堆需要记忆的事实。它是一门要求很高的两年制课程，要求你解释生命系统如何运作、分析实验数据，并将生物学概念应用到陌生的情境中。本入门介绍了剑桥国际 AS 和 A Level 生物（9700）的课程结构、你将接触的核心主题以及取得成功所需的技能。
1. What Is A-Level Biology? | 什么是 A-Level 生物？
Biology is the scientific study of life. At A Level, the subject moves from describing living things to explaining the mechanisms behind them. You will investigate how molecules such as DNA and enzymes control cells, how organisms exchange substances with their environment, and how ecosystems respond to change.
生物学是对生命的科学研究。在 A Level 阶段，这门学科从描述生物体转向解释其背后的机制。你将研究 DNA 和酶等分子如何控制细胞、生物体如何与环境交换物质，以及生态系统如何应对变化。
The Cambridge 9700 syllabus is designed to develop both a strong theoretical foundation and practical competence. You will learn to use a microscope, carry out biochemical tests, plan investigations, and evaluate the reliability of evidence. These are transferable skills that universities and employers value highly.
剑桥 9700 大纲旨在同时培养扎实的理论基础和实践能力。你将学习使用显微镜、进行生化测试、设计实验方案并评估证据的可靠性。这些是可迁移的技能，受到大学和雇主的高度重视。
2. Cambridge 9700 Syllabus at a Glance | 剑桥 9700 大纲一览
The syllabus is divided into 11 core topics at AS Level, with additional depth at A Level. The core topics are listed below. Each topic builds on earlier ones, so a secure grasp of cell biology and biological molecules is essential before moving on to transport, gas exchange and immunity.
该大纲在 AS 阶段分为 11 个核心主题，A Level 阶段进一步加深。核心主题如下。每个主题都建立在前一个主题的基础上，因此在学习运输、气体交换和免疫之前，牢固掌握细胞生物学和生物分子至关重要。
- Cell structure | 细胞结构
- Biological molecules | 生物分子
- Enzymes | 酶
- Cell membranes and transport | 细胞膜与运输
- The mitotic cell cycle | 有丝分裂细胞周期
- Nucleic acids and protein synthesis | 核酸与蛋白质合成
- Transport in plants | 植物运输
- Transport in mammals | 哺乳动物运输
- Gas exchange and smoking | 气体交换与吸烟
- Infectious diseases | 传染病
- Immunity | 免疫
At A Level, you will also study energy and respiration, photosynthesis, homeostasis, control and coordination, inheritance, selection and evolution, and biodiversity. These build directly on the AS core.
在 A Level 阶段，你还将学习能量与呼吸、光合作用、稳态、调控与协调、遗传、选择与进化以及生物多样性。这些内容直接建立在 AS 核心主题之上。
3. The Four Assessment Objectives | 四大评估目标
Every exam question is written against one or more assessment objectives. Understanding these objectives helps you know what the examiner is really testing.
每一道考试题都对应一个或多个评估目标。理解这些目标有助于你了解考官真正考查的内容。
- AO1 Knowledge with understanding: recalling facts, using correct terminology, and explaining concepts. | AO1 知识理解：回忆事实、使用正确术语并解释概念。
- AO2 Handling information and problem solving: interpreting graphs, tables and diagrams, and applying knowledge to new situations. | AO2 信息处理与问题解决：解读图表、表格和示意图，并将知识应用于新情境。
- AO3 Experimental skills and investigations: planning experiments, collecting and recording data, and using apparatus safely. | AO3 实验技能与探究：设计实验、收集和记录数据，并安全使用仪器。
- AO4 Evaluation, conclusions and decision-making: drawing conclusions, identifying limitations, and suggesting improvements. | AO4 评估、结论与决策：得出结论、识别局限性并提出改进建议。
Many high-scoring answers lose marks because students only show AO1. To earn full marks, you must often move beyond recall into analysis, application and evaluation.
许多高分答案因为学生只展示了 AO1 而丢分。要获得满分，你通常必须超越回忆，进入分析、应用和评估层面。
4. Paper Structure and Weighting | 试卷结构与权重
For Cambridge International AS Level, there are three papers: Paper 1 Multiple Choice, Paper 2 AS-Level Structured Questions, and Paper 3 Advanced Practical Skills. For the full A Level, you add Paper 4 A-Level Structured Questions and Paper 5 Planning, Analysis and Evaluation.
剑桥国际 AS 阶段有三份试卷：试卷 1 选择题、试卷 2 AS 结构化问题、试卷 3 高级实验技能。完整 A Level 还需增加试卷 4 A Level 结构化问题和试卷 5 规划、分析与评估。
| Paper | 试卷 | Type | 类型 | Weighting | 权重 |
|---|---|---|
| Paper 1 | 试卷 1 | 40 multiple-choice questions | 40 道选择题 | AS: 31%; A Level: 15.5% |
| Paper 2 | 试卷 2 | Structured questions | 结构化问题 | AS: 46%; A Level: 23% |
| Paper 3 | 试卷 3 | Practical skills assessment | 实验技能评估 | AS: 23%; A Level: 11.5% |
| Paper 4 | 试卷 4 | Structured questions, including extended response | 结构化问题，含扩展作答 | A Level: 38.5% |
| Paper 5 | 试卷 5 | Planning, analysis and evaluation | 规划、分析与评估 | A Level: 11.5% |
The practical papers are not optional add-ons. They test genuine laboratory skills, so you should practise handling apparatus, recording observations and evaluating data regularly throughout the course.
实验试卷不是可有可无的附加部分。它们考查真正的实验室技能，因此你应在整个课程中定期练习仪器操作、记录观察结果和评估数据。
5. Core Theme 1: Cell Structure | 核心主题 1：细胞结构
All living organisms are made of cells. You must know the structure and function of eukaryotic cell organelles, including the nucleus, mitochondria, ribosomes, endoplasmic reticulum, Golgi body, lysosomes, chloroplasts and the cell wall. You should also compare prokaryotic and eukaryotic cells.
所有生物体都由细胞组成。你必须掌握真核细胞细胞器的结构和功能，包括细胞核、线粒体、核糖体、内质网、高尔基体、溶酶体、叶绿体和细胞壁。你还应比较原核细胞和真核细胞。
Microscopy is central to this topic. You will calculate magnification and actual size using the formula below, and you will convert between millimetres, micrometres and nanometres.
显微镜技术是本主题的核心。你将使用以下公式计算放大倍数和实际大小，并在毫米、微米和纳米之间进行换算。
magnification = image size ÷ actual size
放大倍数 = 图像大小 ÷ 实际大小
Be careful with units: 1 mm = 1000 µm and 1 µ exam error is to mix units before dividing, which gives an answer out by a factor of 1000.
注意单位：1 mm = 1000 µm，1 µm = 1000 nm。考试中常见的错误是在相除之前混淆单位，导致答案相差 1000 倍。
6. Core Theme 2: Biological Molecules | 核心主题 2：生物分子
Living organisms are built from carbohydrates, lipids, proteins and nucleic acids. You need to know the monomers, the types of bond formed, and the role of water as a solvent and medium for reactions. Polymerisation and hydrolysis are repeated concepts throughout the course.
生物体由碳水化合物、脂质、蛋白质和核酸构成。你需要了解单体、形成的化学键类型，以及水作为溶剂和反应介质的作用。聚合和水解是整个课程中反复出现的概念。
- Carbohydrates: monosaccharides such as glucose (C₆H₁₂O₆), disaccharides such as sucrose, and polysaccharides such as starch, glycogen and cellulose. | 碳水化合物：单糖如葡萄糖（C₆H₁₂O₆），双糖如蔗糖，以及多糖如淀粉、糖原和纤维素。
- Lipids: triglycerides formed from glycerol and three fatty acids by ester bonds; phospholipids form cell membranes. | 脂质：甘油三酯由甘油和三个脂肪酸通过酯键形成；磷脂构成细胞膜。
- Proteins: chains of amino acids folded into specific three-dimensional shapes; the primary structure determines the final conformation. | 蛋白质：氨基酸链折叠成特定的三维结构；一级结构决定最终构象。
- Nucleic acids: DNA and RNA are polymers of nucleotides, each containing a pentose sugar, a phosphate group and a nitrogenous base. | 核酸：DNA 和 RNA 是核苷酸的聚合物，每个核苷酸含有一个五碳糖、一个磷酸基团和一个含氮碱基。
Water is a polar molecule, which makes it an excellent solvent for ions and polar solutes. It also has a high specific heat capacity and a high latent heat of vaporisation, both of which help organisms regulate temperature.
水是极性分子，因此它是离子和极性溶质的优良溶剂。它还具有高比热容和高汽化潜热，这两者都有助于生物体调节温度。
7. Core Theme 3: Enzymes | 核心主题 3：酶
Enzymes are globular proteins that act as biological catalysts. They lower the activation energy of a reaction without being used up. You must be able to explain the induced-fit model, in which the active site changes shape slightly as the substrate binds.
酶是球状蛋白质，充当生物催化剂。它们降低反应的活化能而自身不被消耗。你必须能够解释诱导契合模型，即底物结合时活性位点形状发生轻微变化。
Enzyme activity is affected by temperature, pH, enzyme concentration and substrate concentration. At low temperatures, molecules have less kinetic energy, so collisions are less frequent. At high temperatures, the enzyme denatures because hydrogen bonds break and the tertiary structure is lost.
酶活性受温度、pH、酶浓度和底物浓度的影响。在低温下，分子动能较低，因此碰撞频率较低。在高温下，酶因氢键断裂、三级结构丧失而变性。
Q₁₀ = rate at (T + 10)°C ÷ rate at T°C
Q₁₀ = （T + 10）°C 时的速率 ÷ T°C 时的速率
Competitive inhibitors bind to the active site and can be overcome by increasing substrate concentration. Non-competitive inhibitors bind elsewhere and change the shape of the active site, so increasing substrate concentration has no effect.
竞争性抑制剂结合活性位点，可通过增加底物浓度来克服。非竞争性抑制剂结合其他部位并改变活性位点的形状，因此增加底物浓度没有效果。
8. Core Theme 4: Cell Membranes and Transport | 核心主题 4：细胞膜与运输
Cell membranes are described by the fluid mosaic model. They consist of a phospholipid bilayer with embedded proteins, cholesterol and glycoproteins. The membrane is selectively permeable, allowing some substances to cross but not others.
细胞膜用流体镶嵌模型描述。它们由磷脂双分子层和嵌入的蛋白质、胆固醇和糖蛋白组成。膜具有选择透过性，允许某些物质通过而阻止其他物质通过。
You need to distinguish between diffusion, facilitated diffusion, osmosis and active transport. Diffusion and facilitated diffusion are passive processes that follow a concentration gradient. Active transport requires energy from ATP to move substances against a gradient, using carrier proteins such as the sodium-potassium pump.
你需要区分扩散、协助扩散、渗透和主动运输。扩散和协助扩散是顺浓度梯度的被动过程。主动运输需要来自 ATP 的能量，利用载体蛋白（如钠钾泵）逆浓度梯度运输物质。
Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane. Water potential is measured in kilopascals (kPa), and pure water has a water potential of 0 kPa.
渗透是水分子通过部分透性膜从水势较高的区域向水势较低的区域净移动。水势以千帕（kPa）为单位，纯水的水势为 0 kPa。
9. Core Theme 5: Genetic Control and Cell Division | 核心主题 5：遗传控制与细胞分裂
The cell cycle consists of interphase, mitosis and cytokinesis. During interphase, DNA is replicated in the S phase so that each chromosome consists of two identical sister chromatids. Mitosis produces two genetically identical daughter cells and is essential for growth, repair and asexual reproduction.
细胞周期包括间期、有丝分裂和胞质分裂。在间期的 S 期，DNA 进行复制，使每条染色体由两条相同的姐妹染色单体组成。有丝分裂产生两个遗传上相同的子细胞，对于生长、修复和无性繁殖至关重要。
You should be able to describe the stages of mitosis: prophase, metaphase, anaphase and telophase. In prophase, chromosomes condense and the nuclear envelope breaks down. In metaphase, chromosomes line up at the equator. In anaphase, sister chromatids are pulled to opposite poles. In telophase, nuclear envelopes reform.
你应能够描述有丝分裂的各个阶段：前期、中期、后期和末期。前期，染色体浓缩，核膜破裂。中期，染色体排列在赤道板。后期，姐妹染色单体被拉向两极。末期，核膜重新形成。
Uncontrolled cell division can lead to cancer. Mutations in oncogenes or tumour suppressor genes disrupt the normal regulation of the cell cycle, causing cells to divide excessively and form tumours.
不受控制的细胞分裂可导致癌症。原癌基因或肿瘤抑制基因的突变破坏细胞周期的正常调控，导致细胞过度分裂并形成肿瘤。
10. Practical Skills: The Experimental Foundation | 实验技能：实验基础
Practical work is not a separate topic but a thread running through the whole course. You will carry out investigations on enzyme activity, diffusion, osmosis, photosynthesis and respiration, among others. For each experiment, you must identify the independent variable, dependent variable and control variables.
实验工作不是一个独立的主题，而是贯穿整个课程的一条主线。你将开展酶活性、扩散、渗透、光合作用和呼吸作用等方面的探究。对于每个实验，你必须确定自变量、因变量和控制变量。
- Use a microscope and an eyepiece graticule to measure cells accurately. | 使用显微镜和目镜测微尺准确测量细胞。
- Carry out biochemical tests: Benedict's test for reducing sugars, iodine test for starch, biuret test for proteins, and emulsion test for lipids. | 进行生化测试：本尼迪克特试剂检测还原糖，碘液检测淀粉，双缩脲试剂检测蛋白质，乳剂测试检测脂质。
- Record data in appropriate tables with correct units and significant figures. | 用合适的表格记录数据，使用正确的单位和有效数字。
- Evaluate sources of error and suggest realistic improvements. | 评估误差来源并提出切合实际的改进建议。
When plotting graphs, choose sensible scales, label axes with units, and draw a line of best fit. If a graph shows a curve, do not force a straight line through the points.
绘制图表时，选择合适的刻度，标注轴和单位，并画出最佳拟合线。如果图形显示曲线，不要强行用直线穿过数据点。
11. Command Words and Exam Technique | 指令词与答题技巧
Command words tell you how to answer a question. Misreading a command word is one of the most common reasons candidates lose marks.
指令词告诉你如何回答问题。误读指令词是考生失分的最常见原因之一。
- State: give a concise answer without explanation. | State：给出简洁的答案，无需解释。
- Describe: say what happens or what something looks like; no need to say why. | Describe：说明发生了什么或某物是什么样子；无需说明原因。
- Explain: give reasons or mechanisms, often using scientific principles. | Explain：给出原因或机制，通常使用科学原理。
- Suggest: apply your knowledge to an unfamiliar situation; there may be more than one correct answer. | Suggest：将知识应用于不熟悉的情境；可能有多个正确答案。
- Compare: give similarities and differences. | Compare：给出相似点和不同点。
- Evaluate: weigh up evidence, identify limitations and make a judgement. | Evaluate：权衡证据，指出局限性并作出判断。
In extended response questions, plan your answer before writing. Use scientific terminology precisely, and make sure your answer addresses every part of the question. A clear, logical structure often earns more marks than a long, disorganised paragraph.
在扩展作答中，动笔前先规划答案。准确使用科学术语，并确保答案涵盖问题的每个部分。清晰、有逻辑的结构通常比冗长、杂乱的段落获得更多分数。
12. How to Use This Course Effectively | 如何有效使用本课程
A Level Biology rewards consistent, active study rather than last-minute cramming. Use spaced repetition to review key definitions, and test yourself regularly with past paper questions under timed conditions.
A Level 生物奖励持续、主动的学习，而不是临时突击。使用间隔重复法复习关键定义，并定期在限时条件下用历年真题进行自测。
Draw annotated diagrams for processes such as mitosis, the fluid mosaic model and the heart. Diagrams help you visualise relationships and are often faster to recall than paragraphs of text.
为有丝分裂、流体镶嵌模型和心脏等过程绘制带注释的示意图。示意图帮助你直观理解关系，通常比大段文字更容易回忆。
Keep a practical logbook of all experiments, including your results, graphs and evaluations. Paper 3 and Paper 5 questions often ask you to apply the same techniques you practised in class, so regular hands-on experience is essential.
为所有实验保留一本实验记录本，包括结果、图表和评估。试卷 3 和试卷 5 中的问题通常要求你应用课堂练习过的相同技术，因此定期动手实践至关重要。
Finally, connect topics together. For example, the structure of a protein explains enzyme specificity, which in turn explains how temperature affects metabolic rate. Making these links is the key to high marks in A Level Biology.
最后，将各主题相互联系。例如，蛋白质的结构解释了酶的专一性，而酶的专一性又解释了温度如何影响代谢速率。建立这些联系是在 A Level 生物中取得高分的关键。
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