📚 Year 12 CAIE Science: Core Knowledge Review | Year 12 CAIE 科学：核心知识点梳理
A strong grasp of core scientific principles is essential for success in Year 12 CAIE AS Level Sciences. This article distils key concepts from Physics, Chemistry and Biology, providing a concise yet comprehensive checklist to guide your revision.
牢固掌握核心科学原理是在 Year 12 CAIE AS Level 科学课程中取得成功的基石。本文提炼了物理、化学和生物的关键概念，提供一份简洁而全面的知识点清单，为复习指明方向。
1. Physics – Measurements and Units | 物理 – 测量与单位
candela (cd). Derived units such as the newton (N = kg m s⁻²) are built from these bases.
所有物理量都用国际单位制的基本单位表示：米 (m)、千克 (kg)、秒 (s)、安培 (A)、开尔文 (K)、摩尔 (mol) 和坎德拉 (cd)。导出单位如牛顿 (N = kg m s⁻²) 由这些基本单位组合而成。
Checking the homogeneity of an equation means verifying that each term has the same base units. This powerful tool catches algebraic errors and reinforces the physical meaning of formulas.
检查方程的齐次性就是验证每一项具有相同的基本单位。这一有力工具能发现代数错误并强化公式的物理意义。
ercentage uncertainty. When propagating errors, for addition and subtraction absolute uncertainties add, while for multiplication and division percentage uncertainties add.
每次测量都带有不确定度，用绝对（±Δx）或百分数表示。在误差传递中，加减运算时绝对不确定度相加，而乘除运算时百分数不确定度相加。
2. Physics – Kinematics | 物理 – 运动学
Motion in a straight line is described using displacement, velocity and acceleration. The four SUVAT equations link these quantities for constant acceleration:
直线运动用位移、速度和加速度描述。四个匀变速运动方程（SUVAT）将这组量联系起来：
v = u + at
s = ut + ½ at²
s = ½ (u + v) t
v² = u² + 2as
ity remains constant, while vertically the object accelerates at g = 9.81 m s⁻² downwards.
对于抛体运动，需要独立分析水平和竖直分量。水平速度保持不变，而竖直方向上物体以 g = 9.81 m s⁻² 向下加速。
3. Physics – Dynamics and Forces | 物理 – 动力学与力
Newton's laws of motion govern all force interactions. The second law defines net force as rate of change of momentum: F = ma is a special case for constant mass.
牛顿运动定律支配着所有力的相互作用。第二定律将合力定义为动量的变化率：对于质量不变的情况，简化为 F = ma。
Free-body diagrams isolate an object and show all forces acting on it. Key forces include weight (mg), normal reaction, tension, friction and air resistance. Equilibrium means net force and net moment both equal zero.
受力图隔离物体并显示所有作用其上的力。关键力包括重力 (mg)、法向反作用力、张力、摩擦力和空气阻力。平衡意味着合外力与合力矩都为零。
ject in rotational equilibrium, sum of clockwise moments equals sum of anticlockwise moments.
力对某点的力矩等于力乘以垂直距离。对于转动平衡的物体，顺时针力矩之和等于逆时针力矩之和。
4. Physics – Waves and Superposition | 物理 – 波与叠加
Progressive waves transfer energy without transferring matter. Transverse waves (e.g. light) oscillate perpendicular to the direction of travel; longitudinal waves (e.g. sound) oscillate parallel to it.
行波传递能量而不传递物质。横波（如光）的振动方向垂直于传播方向；纵波（如声音）的振动方向平行于传播方向。
The wave equation: v = f λ, where v is speed, f frequency and λ wavelength. Intensity is proportional to amplitude squared.
波动方程：v = f λ，其中 v 为波速，f 为频率，λ 为波长。强度与振幅的平方成正比。
When two waves meet, superposition occurs. Constructive interference happens when waves are in phase; destructive when out of phase. Stationary waves form when two identical waves travel in opposite directions, producing nodes and antinodes.
两列波相遇时发生叠加。同相时产生相长干涉；反相时产生相消干涉。两列相同的波沿相反方向传播时形成驻波，产生波节和波腹。
5. Chemistry – Atomic Structure | 化学 – 原子结构
Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells. Atomic number Z is the number of protons; mass number A is protons + neutrons.
原子由包含质子和中子的原子核与核外电子层构成。原子序数 Z 是质子数；质量数 A 是质子数加中子数。
Isotopes are atoms of the same element with different numbers of neutrons. Relative atomic mass is the weighted average mass of an atom relative to 1/12th the mass of carbon‑12.
同位素是同一元素中子数不同的原子。相对原子质量是原子的加权平均质量，以碳‑12 原子质量的 1/12 为标准。
Electrons occupy shells and subshells (s, p, d). Orbitals hold up to two electrons with opposite spins. The first ionisation energy is the energy required to remove one mole of outermost electrons from gaseous atoms.
电子占据电子层和亚层（s、p、d）。轨道最多容纳两个自旋相反的电子。第一电离能是从气态原子中移除一摩尔最外层电子所需的能量。
6. Chemistry – Chemical Bonding | 化学 – 化学键
Ionic bonding involves electrostatic attraction between oppositely charged ions, typically formed when metals transfer electrons to non‑metals. Ionic compounds have high melting points and conduct electricity when molten.
离子键是带相反电荷离子之间的静电吸引，通常由金属向非金属转移电子形成。离子化合物熔点高，熔融时能导电。
Covalent bonding is the sharing of electron pairs between atoms. Simple molecular substances have low melting points, while giant covalent structures like diamond and SiO₂ are extremely strong.
共价键是原子间共享电子对。简单分子物质具有低熔点，而像金刚石和二氧化硅这样的巨型共价结构则极强牢固。
Metallic bonding is the attraction between positive metal ions and a 'sea' of delocalised electrons. This explains electrical conductivity, malleability and ductility.
金属键是正金属离子与离域电子“海洋”之间的吸引。这解释了金属的导电性、延展性和展性。
Electronegativity differences determine bond polarity. A difference of 1.7+ usually indicates ionic character; polar molecules have permanent dipoles, while non‑polar molecules may have instantaneous dipoles giving rise to London forces.
电负性差决定键的极性。差值大于 1.7 通常代表离子性；极性分子具有永久偶极，而非极性分子可产生瞬时偶极，从而形成伦敦力。
7. Chemistry – Energetics and Hess's Law | 化学 – 能量学与赫斯定律
Enthalpy change (ΔH) measures heat energy transferred at constant pressure. Exothermic reactions release heat (ΔH negative); endothermic reactions absorb heat (ΔH positive).
焓变 (ΔH) 衡量恒压下的热传递。放热反应释放热量 (ΔH 为负)；吸热反应吸收热量 (ΔH 为正)。
Standard enthalpy changes are measured under standard conditions (298 K, 100 kPa, 1 mol dm⁻³). Common types include ΔHf⁰ (formation), ΔHc⁰ (combustion) and ΔHr⁰ (reaction).
标准焓变在标准条件下 (298 K、100 kPa、1 mol dm⁻³) 测量。常见类型包括 ΔHf⁰（生成焓）、ΔHc⁰（燃烧焓）和 ΔHr⁰（反应焓）。
Hess's Law states that the total enthalpy change for a reaction is independent of the path taken. It can be calculated using enthalpy cycles, often via ΔHf⁰ or ΔHc⁰ values.
赫斯定律指出，反应的总焓变与路径无关。可以利用焓循环计算，通常借助 ΔHf⁰ 或 ΔHc⁰ 数据。
8. Chemistry – Equilibria | 化学 – 平衡
Dynamic equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction in a closed system. Concentrations remain constant but not necessarily equal.
在封闭系统中，当正反应速率等于逆反应速率时达到动态平衡。各组分的浓度保持不变，但并不一定相等。
Le Chatelier's principle: if a system at equilibrium is subjected to a change in concentration, pressure or temperature, the position of equilibrium shifts to oppose the change. For gaseous equilibria, an increase in pressure favours the side with fewer moles.
勒夏特列原理：如果处于平衡的系统受到浓度、压力或温度变化的影响，平衡位置会移动以削弱这种变化。对于气体平衡，增压有利于总物质的量较少的一侧。
The equilibrium constant Kc has a specific value at a given temperature. Its expression is [products]/[reactants] raised to stoichiometric coefficients. Kc remains constant unless temperature changes.
平衡常数 Kc 在给定温度下有特定数值。其表达式为 [生成物]/[反应物] 的化学计量数次方。除非温度改变，否则 Kc 保持不变。
9. Biology – Cell Structure | 生物 – 细胞结构
Eukaryotic cells contain membrane‑bound organelles: nucleus (stores DNA), mitochondria (site of aerobic respiration), endoplasmic reticulum (protein/lipid synthesis), Golgi apparatus (modifies and packages proteins), and ribosomes (protein synthesis).
真核细胞含有膜包被的细胞器：细胞核（储存 DNA）、线粒体（有氧呼吸场所）、内质网（蛋白质/脂质合成）、高尔基体（修饰和包装蛋白质）以及核糖体（蛋白质合成）。
Prokaryotic cells lack a nucleus and membrane‑bound organelles; their DNA lies free in the cytoplasm as a circular loop. They are typically smaller, with cell walls containing peptidoglycan.
原核细胞没有细胞核和膜包被的细胞器；其 DNA 以环状分子游离在细胞质中。它们通常较小，细胞壁含有肽聚糖。
Viruses are non‑cellular structures composed of a nucleic acid core (DNA or RNA) surrounded by a protein capsid. They rely entirely on host cells for replication.
病毒是非细胞结构，由核酸核心（DNA 或 RNA）和外围的蛋白质衣壳组成。它们完全依赖宿主细胞进行复制。
10. Biology – Biological Molecules | 生物 – 生物分子
Carbohydrates, lipids, proteins and nucleic acids are the four major groups. Monosaccharides (e.g. glucose C₆H₁₂O₆) join by glycosidic bonds to form disaccharides and polysaccharides like starch and cellulose.
碳水化合物、脂质、蛋白质和核酸是四大类生物分子。单糖（如葡萄糖 C₆H₁₂O₆）通过糖苷键连接形成二糖和多糖，如淀粉和纤维素。
Proteins are polymers of amino acids linked by peptide bonds. The primary structure is the sequence of amino acids; secondary structure includes α‑helices and β‑pleated sheets; tertiary structure is the overall 3D folding driven by hydrogen, ionic and disulfide bonds.
蛋白质是由氨基酸通过肽键连接的聚合物。一级结构是氨基酸序列；二级结构包括 α‑螺旋和 β‑折叠；三级结构是由氢键、离子键和二硫键驱动的整体三维折叠。
Enzymes are globular proteins that lower activation energy, providing an active site complementary to the substrate. The induced‑fit model describes how the active site moulds around the substrate. Enzyme activity is affected by temperature, pH and inhibitor molecules.
酶是球状蛋白质，能降低活化能，提供一个与底物互补的活性位点。诱导契合模型描述了活性位点如何包裹底物。酶活性受温度、pH 和抑制剂分子的影响。
11. Biology – Transport Across Membranes | 生物 – 跨膜运输
The fluid‑mosaic model describes the plasma membrane: a phospholipid bilayer with embedded and peripheral proteins. Small non‑polar molecules diffuse freely; charged or large polar molecules require transport proteins.
流动镶嵌模型描述了质膜：磷脂双分子层及其镶嵌和周边蛋白。小的非极性分子可自由扩散；带电或大极性分子需要转运蛋白。
Diffusion is the net movement of particles from a high to low concentration, down their gradient. Facilitated diffusion uses channel or carrier proteins without energy input.
扩散是粒子从高浓度向低浓度的净运动，顺浓度梯度。易化扩散利用通道蛋白或载体蛋白，不消耗能量。
Active transport moves molecules against the concentration gradient using ATP, e.g. the sodium‑potassium pump. Endocytosis and exocytosis are bulk transport processes that require energy and involve vesicle formation.
主动运输利用 ATP 逆浓度梯度移动分子，例如钠钾泵。胞吞和胞吐是大分子运输过程，需要能量并涉及囊泡形成。
Osmosis is the movement of water through a partially permeable membrane from a region of higher water potential to lower water potential. Water potential is influenced by solute and pressure potentials.
渗透作用是水通过部分通透膜从较高水势区域向较低水势区域的运动。水势受溶质势和压力势的影响。
12. Biology – The Immune System | 生物 – 免疫系统
Non‑specific defences include skin, mucous membranes, phagocytosis (by neutrophils and macrophages) and inflammation. These provide a rapid, generalised response to pathogens.
非特异性防御包括皮肤、粘膜、吞噬作用（由中性粒细胞和巨噬细胞执行）和炎症。它们对病原体提供快速、非特异的应答。
Specific immunity involves lymphocytes. B cells produce antibodies that bind to specific antigens, neutralising toxins or marking pathogens for destruction. Memory B cells provide long‑term immunity.
特异性免疫涉及淋巴细胞。B 细胞产生能与特定抗原结合的抗体，中和毒素或标记病原体以破坏。记忆 B 细胞提供长期免疫力。
T cells coordinate the response: T helper cells activate B cells and macrophages; T killer cells destroy infected host cells. Active immunity results from natural infection or vaccination; passive immunity involves receiving antibodies directly.
T 细胞协调应答：辅助性 T 细胞激活 B 细胞和巨噬细胞；杀伤性 T 细胞摧毁受感染的宿主细胞。主动免疫源于自然感染或疫苗接种；被动免疫则直接获得抗体。
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