📚 Essential Concepts Across Units 1-3 | 单元1–3 核心概念总览
Welcome to our comprehensive revision guide for Edexcel International A-Level Combined Science, covering the fundamental knowledge from Units 1, 2 and 3. This resource integrates key ideas from biology, chemistry and physics, helping you strengthen cross-disciplinary links and build the deep understanding required for top exam performance. We will explore cell biology, atomic structure, forces, energy, genetics and much more, with every concept explained clearly in both English and Chinese.
欢迎阅读 Edexcel 国际 A-Level 综合科学复习指南，本文涵盖了单元 1、2 和 3 的基础知识。内容整合了生物、化学和物理的核心思想，帮助大家强化跨学科联系，建立应对高分考试所需的深层理解。我们将探索细胞生物学、原子结构、力、能量、遗传学等众多主题，每个概念都配有清晰的中英双语解释。
1. Cell Structure and Organelles | 细胞结构与细胞器
All living organisms are composed of cells, which are the basic structural and functional units of life. Eukaryotic cells, such as those of animals and plants, contain a membrane-bound nucleus and various organelles that carry out specialised tasks. The nucleus houses genetic material in the form of DNA, while mitochondria are the site of aerobic respiration, releasing energy in the form of ATP.
一切生物体都由细胞构成，细胞是生命的基本结构和功能单位。动物和植物等真核细胞含有有膜包被的细胞核以及执行特定任务的多种细胞器。细胞核储存以 DNA 形式存在的遗传物质，而线粒体是有氧呼吸的场所，能够以 ATP 的形式释放能量。
Ribosomes, found either freely in the cytoplasm or attached to the rough endoplasmic reticulum, are responsible for protein synthesis. Plant cells additionally possess chloroplasts for photosynthesis and a rigid cell wall made of cellulose, which provides structural support. Understanding the relationship between organelle structure and function is essential for explaining how cells maintain homeostasis and respond to their environment.
核糖体在细胞质中游离存在或附着在粗面内质网上，负责蛋白质的合成。植物细胞还拥有进行光合作用的叶绿体，以及由纤维素构成的坚硬细胞壁，为细胞提供结构支撑。理解细胞器的结构与功能之间的关系，对于解释细胞如何维持稳态以及响应环境变化至关重要。
2. Particle Theory and States of Matter | 粒子理论与物质状态
The kinetic particle model explains the behaviour of solids, liquids and gases in terms of the arrangement and motion of particles. In a solid, particles are closely packed in a regular lattice and can only vibrate about fixed positions. As the substance is heated, the particles gain kinetic energy, eventually overcoming the attractive forces that hold them together, leading to melting and then boiling.
动力学粒子模型通过粒子的排列与运动解释了固体、液体和气体的行为。在固体中，粒子紧密排列成规则的晶格，只能在固定位置附近振动。当物质受热时，粒子获得动能，最终克服将它们束缚在一起的吸引作用，导致熔化，继而沸腾。
Diffusion provides experimental evidence for particle motion; perfume spreading across a room or potassium manganate(VII) dissolving in water can be explained by random movement from high to low concentration. Changes of state are physical changes because no new substances are formed, and mass is conserved. These ideas underpin much of the chemistry in Units 1 and 2, from explaining evaporation and condensation to interpreting cooling curves.
扩散现象为粒子运动提供了实验证据；香水在房间内扩散或高锰酸钾在水中溶解都可以用粒子从高浓度向低浓度的无规则运动来解释。状态变化属于物理变化，因为没有新物质生成，且质量守恒。这些观念是单元1和2众多化学内容的基础，从解释蒸发和冷凝，到解读冷却曲线，都离不开它们。
3. Atoms, Elements and Compounds | 原子、元素与化合物
An atom is the smallest particle of an element that retains its chemical properties. It consists of a central nucleus containing protons and neutrons, surrounded by electrons orbiting in shells. The atomic number (Z) defines the element by indicating the number of protons, while the mass number (A) is the sum of protons and neutrons.
原子是保持元素化学性质的最小粒子。它由一个包含质子和中子的原子核以及核外分层排布的电子组成。原子序数（Z）通过表示质子数来定义元素，质量数（A）则是质子与中子数之和。
Isotopes are atoms of the same element with different numbers of neutrons; they have identical chemical properties but different physical properties such as density and mass. When atoms of different elements chemically combine in fixed proportions, compounds are formed. For example, sodium reacts with chlorine to form sodium chloride, an ionic compound with a giant lattice structure. The ability to write balanced chemical equations and interpret formulae is a core skill required throughout the Combined Science specification.
同位素是指质子数相同而中子数不同的同种元素原子；它们化学性质相同，但物理性质（如密度和质量）不同。不同元素的原子按固定比例发生化学结合，便形成化合物。例如钠与氯反应生成氯化钠，这是一种具有巨型晶格结构的离子化合物。书写配平的化学方程式以及解读化学式的能力，是综合科学课程中各部分都要求掌握的核心技能。
4. Chemical Bonding: Ionic, Covalent and Metallic | 化学键：离子键、共价键和金属键
Atoms bond in order to achieve a more stable electronic configuration, often that of a noble gas. Ionic bonding occurs when electrons are transferred from a metal to a non-metal, forming oppositely charged ions that attract each other electrostatically in a giant ionic lattice. Sodium chloride and magnesium oxide are typical examples, and their high melting points are explained by the strong electrostatic forces.
原子通过化学键结合，以达到更稳定的电子构型，通常类似于稀有气体的结构。离子键发生在电子从金属转移到非金属的过程中，形成带相反电荷的离子，并在静电作用下构成巨型离子晶格。氯化钠和氧化镁是典型例子，它们的高熔点可用强大的静电作用力来解释。
Covalent bonding involves the sharing of electron pairs between non-metal atoms. Simple molecular substances, such as water and carbon dioxide, consist of small molecules with weak intermolecular forces, resulting in low melting and boiling points. Giant covalent structures, like diamond and silicon dioxide, have networks of strong covalent bonds throughout, giving them very high melting points and hardness. Metallic bonding, meanwhile, arises from a sea of delocalised electrons surrounding positive metal ions, enabling metals to conduct electricity and be malleable.
共价键涉及非金属原子之间共享电子对。水和二氧化碳等简单分子物质由小分子组成，分子间作用力较弱，因此熔点和沸点较低。金刚石和二氧化硅等巨型共价结构则具有贯穿整体的强共价键网络，赋予它们极高的熔点和硬度。金属键则来自离域电子形成的“电子海”包围着正金属离子，使金属能够导电并具有延展性。
5. Forces and Newton's Laws | 力与牛顿定律
Forces are pushes or pulls that can change the speed, direction or shape of an object. Newton's first law states that an object remains at rest or in uniform motion unless acted upon by a resultant force. This introduces the concept of inertia – the tendency of an object to resist changes in its motion.
力是推或拉的作用，可以改变物体的速度、方向或形状。牛顿第一定律指出，除非受到合外力的作用，物体将保持静止或匀速直线运动状态。这就引入了惯性的概念——物体抵抗其运动状态变化的能力。
Newton's second law provides the quantitative relationship between force, mass and acceleration. It is expressed by the equation
牛顿第二定律给出了力、质量与加速度之间的定量关系，用方程表示为
F = m a
where F is the resultant force in newtons, m is the mass in kilograms and a is the acceleration in metres per second squared. This law is fundamental to solving problems involving inclined planes, connected bodies and terminal velocity.
其中 F 为以牛顿为单位的合外力，m 为以千克为单位的质量，a 为以米每二次方秒为单位的加速度。这个定律是求解涉及斜面、连接体和终端速度等问题的核心。
Newton's third law states that for every action, there is an equal and opposite reaction. These forces act on different objects, so they do not cancel out in a free-body diagram. Recognising force pairs is essential for understanding phenomena such as rocket propulsion and walking friction.
牛顿第三定律指出，每一个作用力都有一个大小相等、方向相反的反作用力。这对力作用在不同物体上，因此在自由体图中不会相互抵消。认识力对，对于理解火箭推进和行走摩擦等现象至关重要。
6. Energy Transfers and Conservation | 能量转移与守恒
Energy cannot be created or destroyed, only transferred from one store to another or between objects. The principle of conservation of energy underpins all calculations involving kinetic energy, gravitational potential energy, thermal energy and work done. Any energy that is 'lost' in a process is in fact dissipated, often as thermal energy to the surroundings.
能量既不可以被创造也不能被消灭，只能从一个能量储存转移到另一个储存，或在物体之间传递。能量守恒原理是所有涉及动能、重力势能、热能以及做功的计算的基础。在某一过程中“损失”的能量实际上是耗散了，通常以热能的形式散失到周围环境中。
The kinetic energy of a moving object is given by
运动物体的动能由下式给出
KE = ½ m v²
and the change in gravitational potential energy when an object is raised through a height h is
而物体被升高 h 时的重力势能变化为
ΔGPE = m g h
² on Earth). Efficiency is calculated as (useful energy output ÷ total energy input) × 100% and is a measure of how well energy transfers reduce unwanted dissipation.
其中 g 为重力场强度（地球表面约为 9.8 m s⁻²）。效率的计算方法为（有用能量输出 ÷ 总能量输入）× 100%，它是衡量能量转移过程中减少不必要耗散程度的指标。
7. Waves and the Electromagnetic Spectrum | 波与电磁波谱
Waves transfer energy without transferring matter. Transverse waves, such as light and water ripples, oscillate perpendicular to the direction of energy transfer, while longitudinal waves, like sound, oscillate parallel to it. Key wave parameters include wavelength (λ), frequency (f), amplitude and wave speed (v), linked by the general wave equation:
波传递能量而不传递物质。横波（如光和水波）的振动方向与能量传递方向垂直，而纵波（如声波）的振动方向与能量传递方向平行。重要的波参数有波长（λ）、频率（f）、振幅和波速（v），它们通过通用波动方程联系起来：
v = f λ
est. All EM waves travel at the same speed in a vacuum, approximately 3.0 × 10⁸ m s⁻¹. Different regions of the EM spectrum are used for communications, medical imaging, thermal imaging and sterilisation, depending on their energy and penetrating ability.
电磁波谱是一个横波家族，范围从波长最长的无线电波到波长最短的伽马射线。所有电磁波在真空中的传播速度相同，约为 3.0 × 10⁸ m s⁻¹。电磁波谱的不同区域根据其能量和穿透能力，分别用于通信、医学成像、热成像和消毒等领域。
Reflection, refraction and total internal reflection are wave phenomena governed by the change in speed at boundaries. Understanding these behaviours is crucial in explaining optical fibres, lenses and how ultrasound is used for foetal scanning and sonar.
反射、折射和全内反射是由波在边界处速度变化所决定的波动现象。理解这些行为对于解释光纤、透镜，以及超声波如何用于胎儿检查和声呐等至关重要。
8. Genetics and Inheritance | 遗传学与遗传
Genes are segments of DNA that code for proteins, and they are located on chromosomes in the nucleus. Alleles are different forms of the same gene. In a diploid organism, one allele is inherited from each parent. A dominant allele masks the effect of a recessive allele when both are present, whereas recessive traits only appear when an organism carries two copies of the recessive allele.
基因是编码蛋白质的 DNA 片段，位于细胞核内的染色体上。等位基因是同一基因的不同形式。在二倍体生物中，一个等位基因来自父本，另一个来自母本。当一个显性等位基因与一个隐性等位基因共同存在时，显性基因会掩盖隐性基因的作用，而隐性性状仅在生物体携带两个隐性等位基因时才会表现出来。
Monohybrid crosses can be predicted using Punnett squares, and the resulting genotypic and phenotypic ratios follow Mendelian patterns. Some characteristics are controlled by multiple alleles or exhibit co-dominance, as seen in human ABO blood groups. Sex determination in humans depends on the inheritance of the X and Y chromosomes: females have XX, males have XY.
单基因杂交可以通过庞纳特方格来预测，由此得到的基因型比例和表型比例遵循孟德尔规律。有些性状由多个等位基因控制，或者表现出共显性，例如人类 ABO 血型系统。人类的性别决定取决于 X 和 Y 染色体的遗传：女性为 XX，男性为 XY。
Understanding genetic variation, mutations and the use of family pedigrees allows scientists to trace inherited disorders such as cystic fibrosis and polydactyly. This knowledge also underpins genetic engineering, selective breeding and the ethical debates surrounding modern biotechnology.
了解遗传变异、突变以及家族系谱图的运用，使科学家能够追踪囊性纤维化和多指症等遗传疾病。这一知识也为基因工程、选择育种以及围绕现代生物技术的伦理辩论提供了基础。
9. The Periodic Table: Trends and Groups | 周期表：趋势与族
The modern periodic table arranges elements in order of increasing atomic number, revealing periodic patterns in electronic configurations and chemical properties. Elements in the same group have the same number of outer-shell electrons, which dictates their reactivity. Group 1, the alkali metals, have one electron in the outer shell and react vigorously with water, forming alkaline hydroxides and hydrogen.
现代周期表按照原子序数递增的顺序排列元素，揭示了电子构型和化学性质的周期性变化规律。同一族的元素具有相同的最外层电子数，这决定了它们的反应活性。第1族碱金属最外层有一个电子，能与水剧烈反应，生成碱性氢氧化物和氢气。
Group 7, the halogens, consist of diatomic molecules such as fluorine, chlorine, bromine and iodine. Their reactivity decreases down the group because the atomic radius increases and the attraction for an incoming electron weakens. Group 0, the noble gases, are chemically inert due to having complete outer electron shells, making them useful in lighting and as inert atmospheres.
第7族卤素由双原子分子组成，如氟、氯、溴和碘。它们的反应活性沿族自上而下递减，因为原子半径增大，对新增电子的吸引力减弱。第0族稀有气体由于具有完整的电子壳层而化学性质不活泼，这使得它们在照明和作为惰性气氛方面很有用处。
Periodic trends also include the change from metallic to non-metallic character across a period, and the variation in atomic radius and electronegativity. Being able to use the periodic table to predict properties and write electron configurations (e.g., 2.8.1 for sodium) is a skill assessed throughout Units 1 and 2.
周期表中的趋势还包括同一周期内从金属性到非金属性的变化，以及原子半径和电负性的递变。能够运用周期表预测性质并书写电子构型（例如钠为 2.8.1），是单元1和2中贯穿始终的考查能力。
10. Stoichiometry and the Mole Concept | 化学计量学与摩尔概念
unt of substance, defined as containing exactly 6.022 × 10²³ elementary entities (Avogadro' itative chemistry, enabling chemists to calculate reacting masses, volumes of gases and solution concentrations.
摩尔是物质的量的单位，定义为恰好包含 6.022 × 10²³ 个基本单元（阿伏伽德罗常数）。任何物质一摩尔的质量，在数值上等于其相对原子质量或相对式量，单位为克。这一概念是定量化学的核心，使化学家能够计算反应质量、气体体积和溶液浓度。
s of hydrogen react with one mole of oxygen to yield two moles of water. Using the formula mass, one can convert moles to grams, and with the molar volume of a gas (24 dm³ mol⁻¹ at room temperature and pressure, RTP), moles can be linked to gas volume.
配平的化学方程式给出了反应物结合和产物生成的摩尔比。例如在反应 2H₂ + O₂ → 2H₂O 中，两摩尔氢气与一摩尔氧气反应生成两摩尔水。利用式量，可以将摩尔转化为克数，再结合气体的摩尔体积（在室温和常压 RTP 下为 24 dm³ mol⁻¹），将摩尔与气体体积联系起来。
Concentration in mol dm⁻³ is calculated as moles of solute divided by volume of solution in dm³. Titration calculations allow determination of unknown concentrations using a standard solution, and are common assessment tasks in Unit 2. Always check for limiting reagents when reactants are not mixed in the exact stoichiometric ratio.
以 mol dm⁻³ 为单位的浓度，可用溶质的摩尔数除以溶液的体积（dm³）来计算。滴定计算则可以利用标准溶液测定未知浓度，这是单元2中常见的考查任务。当反应物未按精确的化学计量比混合时，务必要判断哪一种为限制试剂。
11. Motion Graphs and Kinematics | 运动图像与运动学
Kinematics is the study of motion without considering the forces that cause it. Distance–time graphs and velocity–time graphs offer powerful visual ways to analyse motion. The gradient of a distance–time graph gives speed, while the gradient of a velocity–time graph gives acceleration. The area under a velocity–time graph represents displacement.
运动学是研究物体运动而不考虑其受力原因的学科。距离–时间图和速度–时间图为分析运动提供了强有力的视觉工具。距离–时间图的斜率表示速率，而速度–时间图的斜率表示加速度。速度–时间图下方的面积则代表位移。
For motion with constant acceleration, the SUVAT equations are applied:
对于匀加速运动，可使用以下 SUVAT 方程：
v = u + a t
s = u t + ½ a t²
v² = u² + 2 a s
where s is displacement, u is initial velocity, v is final velocity, a is acceleration and t is time. These equations are essential for solving problems involving free fall, braking distances and projectile motion when air resistance is negligible.
其中 s 为位移，u 为初速度，v 为末速度，a 为加速度，t 为时间。这些方程对于求解涉及自由落体、刹车距离以及忽略空气阻力时的抛体运动问题至关重要。
When air resistance cannot be ignored, objects may reach terminal velocity, where the resultant force is zero and the acceleration ceases. Understanding motion graphs and kinematic models allows students to bridge the abstract concepts of Unit 3 physics with practical contexts such as vehicle safety and sports science.
当空气阻力不能忽略时，物体可能达到终端速度，此时合外力为零，加速度消失。理解运动图像和运动学模型，有助于学生将单元3物理中的抽象概念与交通安全和运动科学等实际情境结合起来。
12. Cross-Unit Connections and Exam Strategy | 跨单元联系与考试策略
Combined Science rewards students who can see the bigger picture by linking concepts across biology, chemistry and physics. For instance, diffusion (Unit 1 biology and Unit 2 chemistry), energy transfers (Unit 1 biology and Unit 3 physics) and particles (Unit 2 chemistry and Unit 3 physics) all require integrated understanding. When revising, actively make notes that connect these themes rather than treating each subject in isolation.
综合科学青睐那些能够将生物、化学和物理概念联系起来进行全局思考的学生。例如，扩散（单元1生物和单元2化学）、能量转移（单元1生物和单元3物理）以及粒子（单元2化学和单元3物理）都需要综合理解。复习时，不妨主动做好笔记，把这些主题联系起来，而不是孤立地对待各个学科。
In the exam, read each question carefully, annotate given data and show all steps of your working, particularly in calculations. For six‑mark extended responses, plan your answer to include scientific reasoning, relevant terminology and real‑world examples where appropriate. Command words such as 'explain', 'compare' and 'evaluate' signal the depth required.
在考试中，仔细审题，标注给出的数据，并展示计算的所有步骤，尤其是在计算题中。对于六分的扩写型简答题，要规划好答案，包括科学推理、相关术语，并在适当的情况下结合现实世界的例子。像“解释”、“比较”和“评价”等指令词暗示了答案所需达到的深度。
Time management is crucial; allocate time in proportion to the marks available. Use the practical investigations described in the specification to reinforce your understanding of how scientific knowledge is derived. Reviewing required practicals will help you answer methodological questions and evaluate limitations of procedures confidently.
时间管理至关重要；要按题目分值比例分配时间。利用课程大纲中描述的实践活动来强化对科学知识由来的理解。复习必做实验将帮助你自信地回答有关研究方法的问题，并评价实验步骤的局限性。
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