📚 GCSE Science Last-Minute Revision Notes | GCSE 科学考前冲刺笔记
As your GCSE Science exams approach, these last-minute revision notes cover the essential facts, equations, and practical skills across Biology, Chemistry and Physics. Use them to boost your confidence and avoid common pitfalls.
随着 GCSE 科学考试临近，这份考前冲刺笔记涵盖了生物学、化学和物理学的核心事实、关键公式和实验技能。用它们增强自信，避免常见错误。
1. Key Equations You Must Memorise | 必须记住的关键公式
v = d ÷ t
Speed equals distance divided by time. v is speed (m/s), d is distance (m) and t is time (s). Always check that the units match before calculating.
速度等于距离除以时间。v 表示速度（米/秒），d 表示距离（米），t 表示时间（秒）。计算前请务必确认单位统一。
a = Δv ÷ t
Acceleration is the change in velocity per unit time. Δv = final velocity – initial velocity. A negative acceleration means deceleration.
加速度是单位时间内速度的变化量。Δv = 末速度 – 初速度。负加速度表示减速。
F = m × a
Resultant force is mass times acceleration. Force is measured in newtons (N), mass in kilograms (kg) and acceleration in m/s².
合力等于质量乘以加速度。力的单位是牛顿 (N)，质量单位是千克 (kg)，加速度单位是米每平方秒 (m/s²)。
W = F × d
Work done is force multiplied by distance moved in the direction of the force. Work is measured in joules (J). Energy transferred equals work done.
做功等于力乘以物体沿力的方向移动的距离。功的单位是焦耳 (J)。转移的能量等于做功的数值。
P = W ÷ t
Power is the rate of doing work or transferring energy. Power is in watts (W), work in joules (J) and time in seconds (s).
功率是做功或能量转移的快慢。功率的单位是瓦特 (W)，功的单位是焦耳 (J)，时间单位是秒 (s)。
V = I × R
Ohm’s law: potential difference equals current multiplied by resistance. V is in volts (V), I in amperes (A) and R in ohms (Ω).
欧姆定律：电位差等于电流乘以电阻。V 的单位是伏特 (V)，I 的单位是安培 (A)，R 的单位是欧姆 (Ω)。
v = f × λ
Wave speed equals frequency times wavelength. v is in m/s, frequency f in hertz (Hz) and wavelength λ in metres (m).
波速等于频率乘以波长。v 的单位是米/秒，频率 f 单位是赫兹 (Hz)，波长 λ 单位是米 (m)。
η = (Euseful ÷ Etotal) × 100%
Efficiency is useful output energy divided by total input energy multiplied by 100%. No machine can be 100% efficient due to energy dissipation.
效率等于有用输出能量除以总输入能量再乘以 100%。由于能量耗散，没有机器可以达到 100% 的效率。
2. Atomic Structure and the Periodic Table | 原子结构与元素周期表
Atoms contain protons (positive), neutrons (neutral) and electrons (negative). The atomic number is the number of protons, and the mass number is protons plus neutrons. Isotopes of an element have the same atomic number but different mass numbers, e.g. ¹²₆C and ¹³₆C.
原子包含质子（带正电）、中子（不带电）和电子（带负电）。原子序数等于质子数，质量数等于质子数与中子数之和。同一元素的同位素具有相同的原子序数但不同的质量数，例如 ¹²₆C 和 ¹³₆C。
Electrons are arranged in shells: 2,8,8… The group number of an element tells you how many electrons are in the outer shell (for Groups 1,2,13–18). The period number indicates the number of occupied shells. Metals are on the left, non-metals on the right.
电子按壳层排列：2,8,8… 元素所处的族数表明最外层电子数（适用于第 1、2、13–18 族）。周期数表示占据的电子层数。金属位于左侧，非金属位于右侧。
3. Bonding: Ionic, Covalent and Metallic | 化学键：离子键、共价键和金属键
Ionic bonding occurs between metals and non-metals. Electrons are transferred from the metal to the non-metal, forming oppositely charged ions. For example, Na → Na⁺ + e⁻, Cl + e⁻ → Cl⁻, resulting in NaCl. Giant ionic lattices have high melting points and conduct electricity when molten or dissolved.
离子键出现在金属与非金属之间。电子从金属原子转移到非金属原子，形成带相反电荷的离子。例如 Na → Na⁺ + e⁻，Cl + e⁻ → Cl⁻，形成 NaCl。巨大的离子晶格具有高熔点，在熔融或溶于水时能导电。
Covalent bonding involves the sharing of electron pairs between non-metal atoms. Simple molecules like H₂O, CO₂ and NH₃ have strong covalent bonds but weak intermolecular forces, leading to low boiling points. Giant covalent structures like diamond, graphite and SiO₂ are very hard and have high melting points.
共价键涉及非金属原子之间共享电子对。像 H₂O、CO₂ 和 NH₃ 这样的简单分子内部有牢固的共价键，但分子间作用力弱，因此沸点低。金刚石、石墨和 SiO₂ 等巨型共价结构则非常坚硬，熔点极高。
Metallic bonding: metal atoms donate electrons into a ‘sea’ of delocalised electrons. This sea allows metals to conduct electricity and heat, and makes them malleable. Alloys are mixtures of metals that are often harder than pure metals.
金属键：金属原子将电子投入一个离域电子的“海洋”中。这种电子海洋使金属能导电、导热，并具有延展性。合金是金属的混合物，通常比纯金属更硬。
4. Cells and Organisation | 细胞与组织
Animal cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells have the same plus a cell wall, a large permanent vacuole and chloroplasts. The nucleus controls the cell, mitochondria release energy through respiration, ribosomes make proteins, and chloroplasts absorb light for photosynthesis.
动物细胞包含细胞核、细胞质、细胞膜、线粒体和核糖体。植物细胞除此之外还有细胞壁、一个大的中央液泡和叶绿体。细胞核控制细胞活动，线粒体通过呼吸释放能量，核糖体合成蛋白质，叶绿体吸收光进行光合作用。
Cells are organised into tissues, tissues into organs, and organs into organ systems. An example is the digestive system: glandular tissue secretes enzymes, muscular tissue churns food, and epithelial tissue lines the gut.
细胞构成组织，组织构成器官，器官构成器官系统。以消化系统为例：腺组织分泌酶，肌肉组织搅拌食糜，上皮组织覆盖肠道内壁。
5. Enzymes: Lock and Key Model | 酶：锁钥模型
Enzymes are biological catalysts that speed up reactions without being used up. The active site has a specific shape complementary to the substrate, like a key fitting a lock. Once the enzyme-substrate complex forms, the reaction occurs and products are released.
酶是生物催化剂，能加快反应速度而自身不被消耗。酶的活性部位具有与底物互补的特定形状，就像钥匙插入锁孔。一旦酶-底物复合物形成，反应随即发生，产物被释放出来。
Each enzyme works best at an optimum temperature and pH. High temperatures or extreme pH can denature the enzyme by changing the shape of the active site permanently, so the substrate can no longer fit. Low temperatures just slow molecular movement but do not denature enzymes.
每种酶都有其最适温度和最适 pH。高温或极端 pH 会改变活性部位形状，导致酶变性且不可逆，底物再也无法与之结合。低温只会减缓分子运动速度，但不会使酶变性。
6. Electricity Basics: Current, Voltage and Resistance | 电学基础：电流、电压和电阻
Electric current is the flow of charge. In a single closed loop, the current is the same everywhere. In a series circuit, current is the same through all components; voltage is shared across them. In a parallel circuit, voltage is the same across each branch, but current splits between branches.
电流是电荷的流动。在单一闭合回路中，各处电流相等。在串联电路中，通过各元件的电流相同，电压则在各元件上分配。在并联电路中，各支路两端的电压相等，但总电流分配到各支路。
Resistance opposes current. Adding resistors in series increases total resistance; adding resistors in parallel decreases total resistance. Use an ammeter in series to measure current and a voltmeter in parallel to measure potential difference.
电阻阻碍电流。串联电阻使总电阻增大；并联电阻使总电阻减小。使用电流表串联测量电流，使用电压表并联测量电压。
7. Forces and Motion Graphs | 力与运动图像
A distance-time graph shows how distance changes with time. A horizontal line indicates the object is stationary. A straight sloping line represents constant speed, and the gradient equals speed. A curved line means acceleration: steepening curve = speeding up, levelling off = slowing down.
距离-时间图显示距离如何随时间变化。水平线表示物体静止。倾斜直线代表匀速运动，其斜率等于速度。曲线表示加速度：越来越陡表示加速，越来越平缓表示减速。
A velocity-time graph shows velocity on the y-axis. A horizontal line means constant velocity. A sloping line shows acceleration (gradient = acceleration). The area under the line represents the displacement (distance travelled in a given direction).
速度-时间图的纵轴是速度。水平线表示速度恒定。斜线表示存在加速度（斜率等于加速度）。图线下的面积代表位移（在指定方向上经过的距离）。
8. Energy Transfers and Efficiency | 能量转移与效率
Energy cannot be created or destroyed, only transferred or stored. For any process, total energy before = total energy after. Common stores include kinetic, gravitational potential, thermal, chemical and elastic potential. Sankey diagrams show energy transfers with arrow widths proportional to energy amounts.
能量既不会凭空产生也不会消失，只能转移或储存。在任何过程中，初态总能量等于末态总能量。常见的能量储存包括动能、重力势能、热能、化学能和弹性势能。桑基图用箭头宽度代表能量的多少，展示能量转移。
Efficiency = useful output energy ÷ total input energy. To improve efficiency, reduce unwanted energy transfers such as friction or heat loss. Lubrication, insulation and streamlining are typical methods.
效率 = 有用输出能量 ÷ 总输入能量。要提高效率，就需减少不必要的能量转移，如摩擦或热量散失。常见的做法包括润滑、保温和流线型设计。
9. Required Practicals: Quick Checklists | 必做实验：快速清单
Microscopy: prepare a thin onion epidermis slide, add iodine stain, focus under low power, then high power. Draw a few cells and label cell wall, nucleus and cytoplasm. Calculate magnification using eyepiece × objective lens.
显微镜实验：制作洋葱表皮薄片，加碘液染色，先在低倍镜下聚焦，再换高倍镜。绘制几个细胞并标注细胞壁、细胞核和细胞质。总放大倍数 = 目镜放大倍数 × 物镜放大倍数。
Enzymes: investigate the effect of pH on amylase activity using starch solution and iodine. Time how long the iodine no longer turns blue-black. Keep temperature constant with a water bath. Repeat at different pH buffers.
酶实验：使用淀粉溶液和碘液研究 pH 对淀粉酶活性的影响。记录碘液不再变蓝黑色所需的时间。用水浴保持恒温，并在不同 pH 缓冲液中重复实验。
Rates of reaction: mix sodium thiosulfate with hydrochloric acid and measure how long it takes for a cross under the flask to disappear. Repeat at different temperatures or concentrations. The rate is proportional to 1/time.
反应速率实验：将硫代硫酸钠与盐酸混合，测量烧杯底下黑十字消失所需的时间。在不同温度或浓度下重复实验。反应速率与 1/时间 成正比。
Resistance of a wire: connect a length of wire in a circuit with an ammeter and a voltmeter. Vary the length, record V and I, calculate R = V/I. Plot R against length – expect a straight line through the origin.
导线电阻实验：将一段导线与电流表、电压表接入电路。改变导线长度，记录电压 V 和电流 I，计算 R = V/I。绘制电阻 R 对长度的关系图，预期为过原点的直线。
Specific heat capacity: measure the mass of a metal block, wrap in insulation, insert a heater and thermometer. Record initial temperature, switch on the heater for a known time, measure final temperature and calculate energy supplied = power × time. Use Q = m × c × Δθ to find c.
比热容实验：称量金属块的质量，包好隔热层，插入加热器和温度计。记录初始温度，通电加热一定时间，测末温。供能 = 功率 × 时间。利用 Q = m × c × Δθ 计算比热容 c。
10. Common Mistakes and Exam Tips | 常见错误与考试技巧
Mistake: confusing mass (kg, amount of matter) with weight (N, force due to gravity). Weight = mass × gravitational field strength. Always use the correct unit.
常见错误：混淆质量（单位 kg，指物质多少）与重量（单位 N，由重力引起的力）。重量 = 质量 × 重力场强度。务必使用正确的单位。
Mistake: forgetting to convert units before substituting into equations. E.g. minutes to seconds, grams to kilograms, cm to m. Write the conversion clearly in your working.
常见错误：代入公式前忘记换算单位，例如分换算为秒、克换算为千克、厘米换算为米。在计算过程中清晰写出换算步骤。
Mistake: ignoring significant figures. Give answers to the same number of significant figures as the least precise data provided, or as required by the question.
常见错误：忽视有效数字。答案的有效数字位数应与题目提供的数据中最不精确的一项一致，或按题目要求给出。
Mistake: drawing a graph without labeled axes with units, and not using a sensible scale. Remember: independent variable on x-axis, dependent variable on y-axis.
常见错误：绘制图表时没有标注带单位的坐标轴，或比例不合理。请记住：自变量放在 x 轴，因变量放在 y 轴。
Mistake: stating that results are ‘accurate’ when you mean ‘reliable’. Accurate means close to the true value; reliable (or precise) means repeated readings are close together. Anomalies should be identified and excluded from means.
常见错误：把结果说成“准确 (accurate)”时，本意却是“可靠 (reliable)”。准确指接近真实值，可靠（或精密）指重复测量值互相接近。异常值应识别出来，计算平均值时予以剔除。
Exam tip: read command words carefully – ‘describe’ means say what happens, ‘explain’ means give a scientific reason, ‘calculate’ means do maths and show your working. Always check the number of marks for guidance on depth.
考试技巧：仔细阅读指令词——“describe（描述）”意为讲述发生了什么，“explain（解释）”需给出科学原因，“calculate（计算）”则要求进行数学运算并写出过程。根据题目分值判断作答的详细程度。
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