📚 IGCSE Edexcel Science 701: Comprehensive Revision Guide | IGCSE 爱德思科学 701 全面复习指南
This guide is designed for students studying the IGCSE Edexcel Science (701) specification. It provides a concise yet thorough overview of the core topics across Biology, Chemistry, and Physics, helping you consolidate key concepts before your examinations. Use the bilingual notes to strengthen both your scientific knowledge and academic vocabulary.
本指南专为学习 IGCSE 爱德思科学（701）课程的学生设计。它精炼而全面地梳理了生物、化学和物理的核心主题，帮助你在考试前巩固关键概念。双语笔记旨在同步提升你的科学知识与学术词汇。
1. The Scientific Method | 科学方法
All scientific investigations begin with a hypothesis, a testable statement predicting the relationship between an independent variable and a dependent variable. The independent variable is deliberately changed, while the dependent variable is measured. Control variables must be kept constant to ensure a fair test. A valid experiment includes repeatable measurements and clear identification of potential risks.
所有科学研究都始于假说——一种可检验的陈述，预测自变量与因变量之间的关系。自变量被有意识地改变，因变量则被测量。控制变量必须保持不变以确保公平测试。一项有效的实验包含可重复的测量以及对潜在风险的明确识别。
When presenting data, use tables with headings that show the quantity and unit, e.g., ‘Temperature / °C’. Graphs should have a line of best fit that may be straight or curved. The reliability of results can be improved by calculating the mean and identifying anomalies. Variables are often linked by proportionality statements, such as ‘the rate of reaction is directly proportional to the concentration’.
呈现数据时，应使用表头带物理量和单位的表格，例如 ‘温度 / °C’。图表应画出最佳拟合线，可以是直线或曲线。通过计算平均值并识别异常值可以提高结果的可靠性。变量之间的关系常用比例语言描述，例如“反应速率与浓度成正比”。
2. Cell Structure and Transport | 细胞结构与运输
All living organisms are composed of cells. Eukaryotic cells, such as animal and plant cells, contain a nucleus, cytoplasm, and a cell membrane. Plant cells also possess a cellulose cell wall, a large permanent vacuole, and chloroplasts for photosynthesis. Prokaryotic cells, like bacteria, lack a true nucleus and membrane-bound organelles; their genetic material is a single loop of DNA.
所有生物体都由细胞组成。真核细胞（如动物和植物细胞）含有细胞核、细胞质和细胞膜。植物细胞还拥有纤维素的细胞壁、一个永久性大液泡以及用于光合作用的叶绿体。原核细胞（如细菌）缺少真正的细胞核与膜包被的细胞器；其遗传物质是一条环状 DNA。
| Feature | Animal Cell | Plant Cell |
| Nucleus | Present | Present |
| Cell wall | Absent | Present (cellulose) |
| Chloroplasts | Absent | Present |
| Vacuole | Small or absent | Large, permanent |
Substances move across cell membranes by diffusion, osmosis, and active transport. Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. Osmosis is the diffusion of water molecules through a partially permeable membrane. Active transport requires energy from respiration to move substances against the concentration gradient.
物质通过扩散、渗透和主动运输进出细胞膜。扩散是粒子沿浓度梯度从较高浓度区域向较低浓度区域的净移动。渗透是水分子通过部分透性膜的扩散。主动运输则需要呼吸作用提供的能量，使物质逆浓度梯度移动。
3. Atoms, Elements and Compounds | 原子、元素与化合物
An atom is the smallest particle of an element that can exist. It consists of a nucleus containing protons (relative charge +1) and neutrons (0), surrounded by electrons (‒1) in shells. The atomic number equals the number of protons, while the mass number equals the total number of protons and neutrons. Isotopes are atoms of the same element with different numbers of neutrons.
原子是能够独立存在的元素的最小粒子。它由一个包含质子（相对电荷 +1）和中子（0）的原子核，以及周围分层排布的电子（‒1）构成。原子序数等于质子数，质量数等于质子数与中子数之和。同位素是质子数相同而中子数不同的同种元素的原子。
Elements are arranged in the Periodic Table in order of increasing atomic number. The group number tells you the number of outer-shell electrons, which determines the chemical properties. For example, Group 1 elements (alkali metals) have one electron in the outer shell and react vigorously with water: 2Na + 2H₂O → 2NaOH + H₂. Formulae of compounds can be deduced using ion charges, e.g., Mg²⁺ and Cl⁻ form MgCl₂.
元素在周期表中按原子序数递增排列。族数表明最外层电子数，这决定了化学性质。例如，第 1 族元素（碱金属）最外层有一个电子，与水剧烈反应：2Na + 2H₂O → 2NaOH + H₂。化合物的化学式可通过离子电荷推导，比如 Mg²⁺ 和 Cl⁻ 生成 MgCl₂。
4. Forces and Motion | 力与运动
Forces are vector quantities, having both magnitude and direction. Scalar quantities, such as speed and mass, have magnitude only. The motion of objects can be described using displacement, velocity, and acceleration. Acceleration (a) is the rate of change of velocity: a = (v – u) / t, where u is initial velocity, v is final velocity, and t is time.
力是矢量，既有大小又有方向。标量（如速率和质量）只有大小。物体的运动可用位移、速度和加速度来描述。加速度 (a) 是速度的变化率：a = (v – u) / t，其中 u 是初速度，v 是末速度，t 是时间。
Newton’s first law states that an object will remain at rest or in uniform motion unless acted upon by a resultant force. His second law is summarised by F = m × a. The resultant force is proportional to mass and acceleration. Newton’s third law reminds us that every action force has an equal and opposite reaction force. Terminal velocity occurs when the air resistance (or drag) acting on a falling object equals its weight, producing zero resultant force and constant speed.
牛顿第一定律指出，除非受到合外力，否则物体会保持静止或匀速直线运动状态。他的第二定律可概括为 F = m × a。合外力与质量和加速度成正比。牛顿第三定律提醒我们，每一个作用力都有一个大小相等、方向相反的反作用力。当作用于下落物体的空气阻力（或拖拽力）与其重力相等时，合外力为零，物体达到终极速度，速度保持恒定。
5. Energy Stores and Systems | 能量储存与系统
Energy can be transferred between different stores: kinetic, gravitational potential, chemical, elastic potential, thermal, magnetic, electrostatic, and nuclear. In a closed system, the total energy is conserved; it cannot be created or destroyed, only transferred. Work is done when a force moves an object: W = F × d. The gravitational potential energy store of an object raised through a height h is Ep = m × g × h.
能量可以在不同的储能库之间传递：动能、重力势能、化学能、弹性势能、热能、磁能、静电势能和核能。在封闭系统中，总能量守恒；能量不会凭空产生或消灭，只能传递。力使物体移动时做了功：W = F × d。被提升高度 h 的物体的重力势能储量为 Ep = m × g × h。
Energy resources can be classified as renewable (solar, wind, tidal, hydroelectric, biomass) or non-renewable (coal, oil, natural gas, nuclear). Many thermal power stations use a fuel to heat water into steam, which drives a turbine connected to a generator. The efficiency of any energy transfer is given by: Efficiency = (useful energy output ÷ total energy input) × 100%.
能源可分为可再生（太阳能、风能、潮汐能、水力发电、生物质能）和不可再生（煤、石油、天然气、核能）两类。许多火力发电站利用燃料将水加热成蒸汽，驱动汽轮机带动发电机。任何能量传递的效率为：效率 =（有用的能量输出 ÷ 总能量输入）× 100%。
6. Bonding and Chemical Reactions | 化学键与化学反应
Atoms form bonds to achieve a full outer electron shell, typically obtaining a stable noble-gas configuration. Ionic bonding occurs between metals and non-metals, where electrons are transferred, creating oppositely charged ions held together by electrostatic forces. Covalent bonding involves the sharing of electron pairs between non-metal atoms, forming molecules such as H₂O, CH₄, and O₂.
原子通过形成化学键来达到稳定的最外层电子结构，通常获得惰性气体的稳定排布。离子键发生在金属与非金属之间，电子发生转移，生成靠静电作用力结合在一起的相反电荷离子。共价键涉及非金属原子之间共用电子对，形成分子，例如 H₂O, CH₄ 和 O₂。
Chemical reactions can be classified as exothermic (releasing energy to the surroundings) or endothermic (absorbing energy). The rate of a reaction can be affected by temperature, concentration (or pressure for gases), surface area of solids, and the presence of a catalyst. Collision theory states that particles must collide with sufficient energy (activation energy) and correct orientation for a reaction to occur.
化学反应可分为放热反应（向环境释放能量）和吸热反应（吸收能量）。反应速率受温度、浓度（或气体的压强）、固体的表面积以及催化剂的影响。碰撞理论指出，粒子必须以足够的能量（活化能）和正确的方向碰撞，反应才会发生。
7. Waves and the Electromagnetic Spectrum | 波与电磁波谱
Waves transfer energy without transferring matter. In transverse waves, the oscillations are perpendicular to the direction of energy transfer (e.g., electromagnetic waves, water ripples). In longitudinal waves, oscillations are parallel to the direction of energy transfer (e.g., sound waves). The wave speed equation is v = f × λ, where v is speed in m/s, f is frequency in Hz, and λ is wavelength in metres.
波传递能量而不传递物质。在横波中，振动方向与能量传递方向垂直（如电磁波、水波）。在纵波中，振动方向与能量传递方向平行（如声波）。波速方程为 v = f × λ，其中 v 是波速 (m/s)，f 是频率 (Hz)，λ 是波长 (m)。
The electromagnetic spectrum, in order of increasing wavelength and decreasing frequency, consists of: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, and radio waves. All EM waves travel at the speed of light in a vacuum (3.0 × 10⁸ m/s). They can be reflected, refracted, and diffracted. Higher-frequency EM waves carry more energy, which is why gamma rays and X-rays are ionising and can damage living cells.
电磁波谱按照波长递增、频率递减的顺序包括：伽马射线、X 射线、紫外线、可见光、红外线、微波和无线电波。所有电磁波在真空中的传播速度均为光速 (3.0 × 10⁸ m/s)。它们能被反射、折射和衍射。频率越高的电磁波携带的能量越多，因此伽马射线和 X 射线具有电离性，可能会损伤活细胞。
8. Genetics, DNA and Evolution | 遗传、DNA与进化
DNA is a double-helix polymer made of nucleotides, each containing a sugar, a phosphate group, and a nitrogenous base (A, T, C, G). A gene is a section of DNA that codes for a specific protein. The order of bases determines the sequence of amino acids in the protein. DNA replicates semi-conservatively before cell division, ensuring each new cell receives an identical copy.
DNA 是一种双螺旋结构的聚合物，由核苷酸组成；每个核苷酸含有一个糖、一个磷酸基团和一个含氮碱基 (A, T, C, G)。基因是编码特定蛋白质的 DNA 片段。碱基的顺序决定了蛋白质中氨基酸的序列。DNA 在细胞分裂前进行半保留复制，确保每个新细胞获得一份完全相同的拷贝。
Inheritance can be explained using monohybrid crosses. Alleles are different versions of the same gene; a dominant allele masks the expression of a recessive allele. A homozygous individual has two identical alleles, while a heterozygous individual has two different alleles. Evolution by natural selection occurs when there is genetic variation within a population, and individuals with advantageous characteristics are more likely to survive and reproduce, passing the favourable alleles to their offspring.
遗传可以通过单基因杂交来解释。等位基因是同一基因的不同形式；显性等位基因会掩盖隐性等位基因的表达。纯合子个体具有两个相同的等位基因，杂合子个体则具有两个不同的等位基因。自然选择导致的进化过程如下：种群内存在遗传变异，具有有利特征的个体更有可能存活并繁殖，从而将优势等位基因传递给后代。
9. Homeostasis and the Nervous System | 稳态与神经系统
Homeostasis is the maintenance of a stable internal environment. Key examples include control of blood glucose concentration, body temperature, and water balance. The nervous system enables rapid communication between receptors and effectors. Sensory neurones carry impulses from receptors to the central nervous system (CNS), relay neurones process the information, and motor neurones send impulses to effectors such as muscles or glands.
稳态是身体内部环境维持稳定的状态。主要例子包括血糖浓度调节、体温控制和水盐平衡。神经系统使感受器与效应器之间能快速通讯。感觉神经元将神经冲动从感受器传至中枢神经系统 (CNS)，中间神经元处理信息，运动神经元将冲动传递给效应器，如肌肉或腺体。
A reflex arc bypasses conscious thought and follows a precise path: stimulus → receptor → sensory neurone → relay neurone (in spinal cord) → motor neurone → effector → response. At the synapse, a chemical transmitter substance diffuses across the gap to trigger a new impulse. The endocrine system complements the nervous system by releasing hormones, which travel in the blood and produce slower, longer-lasting responses.
反射弧绕过了意识思维，遵循精确的通路：刺激 → 感受器 → 感觉神经元 → 中间神经元（在脊髓中）→ 运动神经元 → 效应器 → 反应。在突触处，化学递质扩散越过间隙，触发新的神经冲动。内分泌系统通过释放激素来配合神经系统，激素随血液流动，引起较缓慢但更持久的反应。
10. Electricity and Circuits | 电与电路
Electric current is the rate of flow of charge: I = Q / t. In metallic conductors, current is a flow of electrons. Potential difference (voltage) is the energy transferred per unit charge passed: V = E / Q. Resistance opposes the flow of current and is measured in ohms (Ω): R = V / I. The behaviour of a component can be shown on an I-V characteristic graph.
电流是电荷流动的速率：I = Q / t。在金属导体中，电流是电子的流动。电势差（电压）是单位电荷通过时传递的能量：V = E / Q。电阻阻碍电流的流动，单位为欧姆 (Ω)：R = V / I。元件的特性可以通过 I-V 特性曲线图表示。
In a series circuit, the current is the same at all points, but the potential difference is divided across components. The total resistance R_total = R₁ + R₂ + … In a parallel circuit, the potential difference is the same across each branch, while the total current equals the sum of the branch currents. The total resistance of parallel resistors is less than the smallest individual resistance. Mains electricity is AC and operates at 230 V (in many countries), requiring live, neutral, and earth wires for safety.
在串联电路中，各处电流相同，而电势差在元件之间被分割。总电阻 R_total = R₁ + R₂ + … 在并联电路中，各支路两端电势差相同，而总电流等于各支路电流之和。并联电阻的总电阻小于其中最小的单个电阻。市电是交流电，电压通常为 230 V（多国），需要配备火线、零线和地线以确保安全。
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