📚 Edexcel IAL Combined Science Unit 1 (107): Molecules, Diet, Transport and Health | Edexcel 国际 A-Level 综合科学第一单元(107)：分子、饮食、运输与健康
This revision guide covers the core principles assessed in Edexcel International Advanced Level Combined Science Unit 1 (code 107) – Molecules, Diet, Transport and Health. It integrates essential topics from biology, chemistry and physics to help you master key concepts for the examination. Each section presents bilingual content with clear explanations, diagrams in words, and memory aids designed for the Edexcel specification.
本复习指南涵盖 Edexcel 国际 A-Level 综合科学第一单元（试卷代码 107）——分子、饮食、运输与健康的核心原理。它整合了生物、化学和物理的重要主题，帮助掌握考试关键概念。每一节都以双语呈现清晰的解释、文字图解和针对 Edexcel 考试大纲的记忆技巧。
1. Introduction to Biological Molecules | 生物分子导论
All living organisms are built from a small set of carbon-based compounds. The key biological molecules are carbohydrates, lipids, proteins and nucleic acids. They form the basis of diet, metabolism and health. In Combined Science 107, you need to recognise the structures and functions of these molecules and relate them to properties such as solubility and energy storage.
所有生物体都由一小套碳基化合物构成。关键的生物分子包括碳水化合物、脂质、蛋白质和核酸。它们构成了饮食、新陈代谢和健康的基础。在综合科学 107 中，你需要识别这些分子的结构和功能，并将其与溶解性、能量储存等性质联系起来。
2. Carbohydrates: Monosaccharides to Polysaccharides | 碳水化合物：从单糖到多糖
Carbohydrates are composed of carbon, hydrogen and oxygen, often in the ratio (CH₂O)ₙ. Monosaccharides like glucose (C₆H₁₂O₆) are simple sugars that act as energy sources. Glucose exists as two isomers: α-glucose and β-glucose, differing only in the position of the –OH group on carbon 1. This small change leads to distinct polymers.
碳水化合物由碳、氢、氧组成，通常比例为 (CH₂O)ₙ。像葡萄糖 (C₆H₁₂O₆) 这样的单糖是简单的能量来源。葡萄糖有两种异构体：α-葡萄糖和 β-葡萄糖，仅在第 1 号碳上 –OH 基团的位置不同。这一微小变化导致了不同的聚合物。
α-glucose molecules link to form starch and glycogen, both used for energy storage. Amylose, a component of starch, forms a coiled, unbranched chain, whereas glycogen is highly branched for rapid release of glucose. In contrast, β-glucose forms cellulose, with straight, linear chains that hydrogen-bond together to produce strong fibres essential for plant cell walls.
α-葡萄糖分子连接形成淀粉和糖原，两者都用于能量储存。淀粉的组分直链淀粉呈螺旋状、无支链；糖原则高度支化以便快速释放葡萄糖。相反，β-葡萄糖构成纤维素，形成直链并通过氢键聚合，产生植物细胞壁必需的强韧纤维。
The test for starch uses iodine solution, which turns from yellow-brown to blue-black in the presence of the coiled amylose. Benedict's test for reducing sugars (like glucose) produces a brick-red precipitate upon heating with Benedict's reagent.
淀粉检测使用碘液，在有螺旋直链淀粉存在时由黄褐色变为蓝黑色。本尼迪克特试验检测还原糖（如葡萄糖），加热后与本尼迪克特试剂产生砖红色沉淀。
| Polysaccharide | Monomer | Bonding | Function |
|---|---|---|---|
| Starch (amylose) | α-glucose | 1,4-glycosidic | Plant energy store |
| Glycogen | α-glucose | 1,4 & 1,6-glycosidic | Animal energy store |
| Cellulose | β-glucose | 1,4-glycosidic | Plant cell wall structure |
3. Lipids and Triglycerides | 脂质与甘油三酯
Lipids are hydrophobic organic molecules that include triglycerides, phospholipids and steroids. Triglycerides are formed by the condensation of one glycerol molecule and three fatty acids. Each fatty acid chain is attached via an ester bond, and three water molecules are released per triglyceride synthesised.
脂质是疏水性有机分子，包括甘油三酯、磷脂和类固醇。甘油三酯由一个甘油分子和三个脂肪酸经缩合反应形成。每条脂肪酸链通过酯键连接，每合成一个甘油三酯释放三分子水。
uid at room temperature). The degree of saturation influences membrane fluidity and health – a diet high in saturated fats is associated with increased risk of cardiovascular disease.
脂肪酸可以是饱和的（碳原子间无双键，室温呈固态）或不饱和的（含一个或多个 C=C 双键，室温呈液态）。饱和度影响膜的流动性和健康——高饱和脂肪饮食与心血管疾病风险增加相关。
The emulsion test for lipids involves adding ethanol to a sample, shaking, and then pouring into water. A milky-white emulsion indicates the presence of lipids. This simple test exploits the insolubility of lipids in water and solubility in ethanol.
脂质的乳浊试验：将乙醇加入样品，摇匀后倒入水中。出现乳白色乳浊液表明存在脂质。这一简易检测利用了脂质不溶于水而溶于乙醇的特性。
4. Proteins: Structure and Enzymes | 蛋白质：结构与酶
Proteins are polymers of amino acids linked by peptide bonds. The primary structure is the linear sequence of amino acids. Secondary structure refers to local folding into α-helices and β-pleated sheets, stabilised by hydrogen bonds. Tertiary structure is the overall 3D conformation, held by hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic interactions. Quaternary structure exists in proteins with multiple polypeptide chains, such as haemoglobin.
蛋白质是由肽键连接的氨基酸聚合物。一级结构是氨基酸的线性序列。二级结构指局部折叠成 α-螺旋和 β-折叠片，由氢键稳定。三级结构是整体的三维构象，由氢键、离子键、二硫键和疏水作用维持。具有多条多肽链的蛋白质具有四级结构，如血红蛋白。
Enzymes are globular proteins that act as biological catalysts. They lower activation energy by providing an alternative reaction pathway. The active site is a specific shape complementary to the substrate – described by the lock-and-key model or, more accurately, the induced-fit model, where the active site moulds around the substrate.
酶是球状蛋白质，发挥生物催化剂作用。它们通过提供替代反应路径来降低活化能。活性位点具有与底物互补的特异形状——可用锁钥模型描述，或更准确的诱导契合模型，即活性位点在底物周围发生形变。
Enzyme activity is affected by temperature, pH, substrate concentration and inhibitors. At very high temperatures, enzymes denature: the tertiary structure breaks down and the active site loses its complementary shape. Competitive inhibitors bind to the active site, while non-competitive inhibitors bind elsewhere and change the shape of the active site.
酶活性受温度、pH、底物浓度和抑制剂影响。在高温下酶会变性：三级结构破坏，活性位点丧失互补形状。竞争性抑制剂结合于活性位点，而非竞争性抑制剂结合于别处并改变活性位点的形状。
5. Diet, Digestion and Health | 饮食、消化与健康
A balanced diet provides all necessary nutrients: carbohydrates, fats, proteins, vitamins, minerals, fibre and water. Energy requirements vary with age, activity levels and pregnancy. BMI (body mass index) and waist-to-hip ratio are used to assess whether a person is underweight, normal, overweight or obese. Obesity increases the risk of coronary heart disease, type 2 diabetes and some cancers.
均衡饮食提供所有必需营养素：碳水化合物、脂肪、蛋白质、维生素、矿物质、膳食纤维和水。能量需求因年龄、活动量和怀孕状况而异。体质量指数（BMI）和腰臀比用于评估体重不足、正常、超重或肥胖。肥胖会增加冠心病、2型糖尿病和某些癌症的风险。
Digestion involves the breakdown of large, insoluble molecules into small, soluble ones that can be absorbed. Carbohydrases (e.g. amylase) digest starch into maltose and glucose. Proteases break proteins into amino acids. Lipases, assisted by bile salts that emulsify fats, hydrolyse triglycerides into fatty acids and glycerol. Absorption occurs mainly in the small intestine, where villi and microvilli provide a large surface area.
消化涉及将大分子、不溶性物质分解为可吸收的小分子、可溶性物质。糖酶（如淀粉酶）将淀粉分解为麦芽糖和葡萄糖。蛋白酶将蛋白质分解为氨基酸。脂肪酶在胆汁盐乳化脂肪的协助下，将甘油三酯水解为脂肪酸和甘油。吸收主要在小肠进行，绒毛和微绒毛提供了巨大的表面积。
6. Gas Exchange and Circulatory Systems | 气体交换与循环系统
In mammals, gas exchange occurs in the alveoli of the lungs. Alveoli are surrounded by a dense network of capillaries, and their walls are one cell thick, minimising the diffusion distance. Oxygen diffuses from alveolar air into the blood, while carbon dioxide diffuses in the opposite direction. The process is facilitated by the steep concentration gradient maintained by ventilation and continuous blood flow.
哺乳动物的气体交换在肺泡中进行。肺泡被致密的毛细血管网包围，其壁只有一个细胞厚，最大限度地缩短了扩散距离。氧气从肺泡气扩散到血液，二氧化碳则反向扩散。通气和持续的血液流动维持着较高的浓度梯度，促进了这一过程。
The heart is a double pump: the right side sends deoxygenated blood to the lungs (pulmonary circulation), and the left side pumps oxygenated blood to the rest of the body (systemic circulation). The cardiac cycle involves atrial systole, ventricular systole and diastole. Atherosclerosis, a buildup of fatty plaques in arteries, can lead to angina, heart attacks and strokes.
心脏是一个双重泵：右侧将缺氧血送往肺部（肺循环），左侧将富氧血泵至身体各处（体循环）。心动周期包括心房收缩、心室收缩和舒张。动脉粥样硬化即动脉内脂肪斑块堆积，可能导致心绞痛、心脏病发作和中风。
7. Transport in Plants | 植物的运输
Xylem transports water and dissolved mineral ions from roots to leaves. The flow is driven by transpiration – the evaporation of water from mesophyll cells into leaf air spaces and out through stomata. Cohesion and adhesion produce tension that pulls the water column up, as described by the cohesion-tension theory. Xylem vessels are dead, lignified tubes with no end walls, allowing unimpeded flow.
木质部将水和溶解的矿物离子从根部运送到叶片。蒸腾作用驱动这一流动——水分从叶肉细胞蒸发到叶片气隙，再通过气孔散失。内聚力和附着力产生张力，将水柱向上拉，这由内聚力-张力理论描述。木质部导管是死细胞、木质化的管子，无端壁，使流动畅通无阻。
Phloem transports sucrose and amino acids from sources (e.g. leaves) to sinks (e.g. roots, fruits) by translocation. The process is energy-dependent (active transport at the source and companion cells) and explained by the mass flow hypothesis. Translocation moves organic substances in both directions, unlike xylem flow which is unidirectional.
韧皮部通过转运将蔗糖和氨基酸从源（如叶片）运输到库（如根、果实）。这一过程依赖能量（在源和伴胞处进行主动运输），并可用压力流动假说解释。与木质部的单向流动不同，转运可双向移动有机物。
8. Atomic Structure and Bonding (Chemistry) | 原子结构与键合（化学）
Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells. The atomic number (Z) is the number of protons, which defines the element. Isotopes have the same Z but different numbers of neutrons. The relative atomic mass Aᵣ is the weighted mean mass of an atom relative to 1/12 the mass of carbon-12.
原子由包含质子和中子的原子核以及分层分布的电子组成。原子序数 (Z) 是质子数，决定了元素种类。同位素具有相同的 Z 但中子数不同。相对原子质量 Aᵣ 是原子质量相对于碳‑12 原子质量 1/12 的加权平均值。
Ionic bonding occurs between metals and non-metals, involving electron transfer to form oppositely charged ions that attract each other in a giant ionic lattice. Covalent bonding involves the sharing of electron pairs between atoms. Simple molecular substances (e.g. H₂O, CO₂) have weak intermolecular forces and low melting points, while giant covalent structures (diamond, graphite) have high melting points. Metallic bonding consists of a lattice of positive ions in a sea of delocalised electrons, enabling electrical conductivity and malleability.
离子键存在于金属和非金属之间，通过电子转移形成带相反电荷的离子，在巨型离子晶格中彼此吸引。共价键涉及原子间共用电子对。简单分子物质（如 H₂O, CO₂）分子间力弱，熔点低，而巨型共价结构（金刚石、石墨）熔点很高。金属键由正离子晶格浸在离域电子海中构成，赋予金属导电性和延展性。
9. Introduction to Organic Chemistry: Alkanes and Alkenes | 有机化学导论：烷烃与烯烃
Organic chemistry is the study of carbon compounds. Alkanes are saturated hydrocarbons with the general formula CₙH₂ₙ₊₂. They contain only single C–C bonds and undergo substitution reactions with halogens in the presence of UV light. For example, methane reacts with chlorine to form chloromethane and hydrogen chloride via a free-radical mechanism.
有机化学是碳化合物化学。烷烃是通式为 CₙH₂ₙ₊₂ 的饱和烃。它们仅含单 C–C 键，在紫外光下与卤素发生取代反应。例如，甲烷与氯气反应，通过自由基历程生成氯甲烷和氯化氢。
le bond (unsaturated) with general formula CₙH₂ₙ. The double bond is an area of high electron density, making alkenes more reactive than alkanes. Characteristic reactions include electrophilic addition. Ethene reacts with bromine water, turning it from orange to colourless, in an addition reaction. Alkenes can also undergo addition polymerisation, producing poly(ethene) and other important plastics.
烯烃至少含一个 C=C 双键（不饱和），通式为 CₙH₂ₙ。双键是高电子密度区域，使烯烃比烷烃更活泼。特征反应包括亲电加成。乙烯与溴水发生加成反应，使溴水由橙色变为无色。烯烃还可发生加成聚合，生成聚（乙烯）等重要塑料。
10. Mechanics: Motion and Forces | 力学：运动与力
nt acceleration (SUVAT) are essential. For example, v = u + at, s = ½(u + v)t, s = ut + ½at², and v² = u² + 2as. Velocity– phs provide acceleration from the gradient and displacement from the area under the curve.
运动学用位移、速度、加速度和时间等物理量描述物体的运动。匀加速运动的方程（SUVAT）至关重要。例如，v = u + at，s = ½(u + v)t，s = ut + ½at²，v² = u² + 2as。速度–时间图中，斜率表示加速度，曲线下面积表示位移。
Newton' force. The second law defines resultant force F = ma. The third law states that if body A exerts a force on body B, then B exerts an equal and opposite force on A. Free-body diagrams are used to resolve forces and analyse equilibrium.
牛顿运动定律是所有力分析的基础。第一定律：物体在不受外力作用时保持静止或匀速直线运动。第二定律：合力 F = ma。第三定律：若物体 A 对 B 施加力，则 B 对 A 施加大小相等、方向相反的力。受力分析图用于分解力并分析平衡。
11. Materials: Stress, Strain and Young Modulus | 材料：应力、应变与杨氏模量
train (ε) is the extension per unit original length: ε = ΔL/L₀. Both are dimensionless proportions or measured in pascals for stress. The Young modulus (E) is a measure of stiffness, given by E = σ/ε within the linear elastic region.
材料的力学性质由应力和应变描述。应力 (σ) 是单位截面积上施加的力：σ = F/A。应变 (ε) 是单位原长上的伸长量：ε = ΔL/L₀。应力单位为帕斯卡，应变为无量纲比例。杨氏模量 (E) 是刚度的量度，在线性弹性范围内 E = σ/ε。
A typical stress–strain curve for a ductile material shows a linear elastic region, followed by plastic deformation, necking and fracture. The limit of proportionality is the point beyond which the force–extension graph is no longer linear. The tensile strength or ultimate tensile stress is the maximum stress a material can withstand before fracture.
典型韧性材料的应力–应变曲线展示线弹性区，随后是塑性变形、颈缩和断裂。比例极限是力–伸长图不再呈线性的点。抗拉强度或极限拉伸应力是材料断裂前所能承受的最大应力。
Elastic strain energy is the energy stored in a deformed material that can be recovered. It is equal to the area under the force–extension graph for the elastic region. The energy per unit volume is ½σε for a linear elastic material.
弹性应变能是形变材料可恢复的储存能量，等于弹性区域内力–伸长图下的面积。对于线弹性材料，单位体积能量为 ½σε。
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