IGCSE WJEC Science: Last-Minute Revision Notes | IGCSE WJEC 科学：考前冲刺笔记

📚 IGCSE WJEC Science: Last-Minute Revision Notes | IGCSE WJEC 科学：考前冲刺笔记

This set of last-minute revision notes covers the essential topics for the IGCSE WJEC Science (Double Award) specification. Use it to quickly review key concepts in biology, chemistry and physics before your exam.

这套考前冲刺笔记涵盖了 IGCSE WJEC 科学（双奖）考试的核心主题，帮助你在考前快速回顾生物、化学和物理的关键概念。

1. Cell Biology & Life Processes | 细胞生物学与生命过程

Understanding cell structure and life processes is fundamental in biology. All living organisms are made of cells, and the functions of cellular components are tightly linked to their structures.

理解细胞结构和生命过程是生物学的基础。所有生物都由细胞构成，细胞组分的功能与其结构紧密相关。

Animal cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells additionally have a cellulose cell wall, a large permanent vacuole and chloroplasts for photosynthesis.

动物细胞包含细胞核、细胞质、细胞膜、线粒体和核糖体。植物细胞还有纤维素细胞壁、中央大液泡和进行光合作用的叶绿体。

Enzymes are biological catalysts that speed up reactions without being used up. They are specific to substrates and work best at an optimum temperature and pH. Denaturation occurs if conditions become too extreme.

酶是生物催化剂，能加快反应且自身不被消耗。酶对底物具有专一性，并在最适温度和pH下活性最高。条件过于剧烈时酶会变性。

Movement of substances: Diffusion is the net movement of particles from a region of higher concentration to lower concentration. Osmosis is the diffusion of water across a partially permeable membrane. Active transport requires energy to move substances against a concentration gradient.

物质运动：扩散是粒子从高浓度区域向低浓度区域的净运动。渗透是水通过部分透膜的扩散。主动运输需要能量将物质逆浓度梯度移动。

Magnification = image size ÷ actual size (M = I/A)

放大倍数 = 图像大小 ÷ 实际大小

2. Atomic Structure & the Periodic Table | 原子结构与周期表

Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons arranged in shells. Protons carry a positive charge, electrons a negative charge, and neutrons have no charge.

原子由包含质子和中子的原子核及核外分层排布的电子组成。质子带正电荷，电子带负电荷，中子不带电。

The atomic number equals the number of protons; the mass number is the total number of protons and neutrons. Isotopes are atoms of the same element with different numbers of neutrons but identical chemical properties.

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但中子数不同的同种元素的原子，化学性质相同。

Electron arrangement: the first shell holds up to 2 electrons, the second and third shells hold up to 8. Elements in the same group of the periodic table have the same number of outer electrons, giving them similar reactivity.

电子排布：第一层最多容纳 2 个电子，第二、三层各最多容纳 8 个。同一族的元素最外层电子数相同，因此化学性质相似。

The periodic table is arranged by increasing atomic number. Metals are on the left, non-metals on the right, and noble gases (Group 0) are unreactive because they have a full outer shell.

周期表按原子序数递增排列。金属在左，非金属在右，稀有气体（0 族）因最外层满电子而化学性质极不活泼。

3. Chemical Bonding & Reactions | 化学键与化学反应

Ionic bonding occurs when electrons are transferred from a metal to a non-metal, forming oppositely charged ions that attract each other in a giant lattice. Ionic compounds have high melting points and conduct electricity when molten or dissolved.

离子键中电子从金属转移给非金属，形成正负离子并在巨型晶格中相互吸引。离子化合物熔点高，熔融或溶于水时能导电。

Covalent bonding involves non-metal atoms sharing pairs of electrons. Simple molecular substances such as H₂O and CO₂ have low melting points, while giant covalent structures like diamond and silicon dioxide have very high melting points.

共价键是非金属原子通过共用电子对结合。简单分子物质如 H₂O 和 CO₂ 熔点低，而金刚石、二氧化硅等巨型共价结构熔点极高。

Metallic bonding is formed by a lattice of positive ions surrounded by a sea of delocalised electrons, which explains the electrical conductivity and malleability of metals

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