📚 GCSE WJEC Science: Clarifying Common Misconceptions | GCSE WJEC 科学：概念辨析
In GCSE WJEC Science, students often lose marks not because they do not know the science, but because they confuse similar-sounding terms. This article clarifies twelve pairs of commonly misunderstood concepts across physics, chemistry and biology, and explains exactly how WJEC mark schemes expect you to use them, so you can avoid those tricky exam pitfalls.
在 GCSE WJEC 科学考试中，学生失分往往不是因为不懂科学，而是因为混淆了听起来相似的术语。本文辨析物理、化学和生物三科中十二对常见的易混概念，并说明 WJEC 评分标准究竟希望你如何使用这些术语，帮助你避开考试中的那些陷阱。
1. Mass vs Weight | 质量与重量
Mass is the quantity of matter in an object. It is a scalar quantity, meaning it has magnitude only and no direction. Mass is measured in kilograms (kg) using a balance, and it does not change when the object is moved to a different planet.
质量是物体所含物质的多少。它是标量，只有大小、没有方向。质量用天平以千克（kg）为单位测量，物体被移到不同星球上时质量不会改变。
Weight, on the other hand, is the gravitational force acting on an object. It is a vector quantity, having both magnitude and direction (downwards, towards the centre of the Earth). Weight is measured in newtons (N) using a spring balance or force meter. The weight of an object can be calculated using the formula:
另一方面，重量（重力）是作用在物体上的引力。它是矢量，既有大小也有方向（竖直向下，指向地心）。重量用弹簧秤或测力计以牛顿（N）为单位测量。物体的重量可用下面的公式计算：
W = m × g
where W is weight in newtons, m is mass in kilograms and g is the gravitational field strength in newtons per kilogram (about 9.8 N/kg on Earth and about 1.6 N/kg on the Moon).
其中 W 是重量（牛顿），m 是质量（千克），g 是重力场强度（牛顿每千克），在地球上约为 9.8 N/kg，在月球上约为 1.6 N/kg。
| Quantity 量 | Type 类型 | Unit 单位 | Measured with 测量工具 |
| Mass 质量 | Scalar 标量 | kg | Balance 天平 |
| Weight 重量 | Vector 矢量 | N | Force meter 测力计 |
Exam trap: if a WJEC question asks you to 'state the weight' of a 2 kg bag of sugar, the answer is 19.6 N, not 2 kg. Writing the mass when the question asks for weight is one of the most commonly penalised errors.
考试陷阱：如果 WJEC 题目要求你“写出”一袋 2 kg 白糖的重量，答案应是 19.6 N，而不是 2 kg。题目问重量却答质量，是最常见的失分错误之一。
2. Speed vs Velocity | 速率与速度
Speed is a scalar quantity: it tells you how fast something is moving, with no reference to direction. It is calculated as distance travelled divided by time taken, and is measured in metres per second (m/s).
速率是标量：只说明物体运动得多快，不涉及方向。它等于通过的路程除以所用时间，单位是米每秒（m/s）。
Velocity is a vector quantity: it is displacement divided by time, so it includes a direction. Displacement is the straight-line distance from start to finish, which is why a runner who completes one 400 m lap has travelled 400 m but has a displacement of zero — and therefore an average velocity of zero.
速度是矢量：它等于位移除以时间，因此必须包含方向。位移是从起点到终点的直线距离，所以跑完一圈 400 m 的运动员路程是 400 m，但位移为零——因此平均速度也为零。
speed = distance ÷ time v = s ÷ t
On a distance–time graph the gradient gives speed; on a velocity–time graph the gradient gives acceleration and the area under the line gives the distance travelled. WJEC frequently tests these three relationships together.
在距离—时间图像中，斜率代表速率；在速度—时间图像中，斜率代表加速度，图线下的面积代表路程。WJEC 经常把这三个关系放在一起考查。
3. Energy vs Power | 能量与功率
/s. Power tells you how quickly energy is transferred, not how much energy is transferred.
能量是做功的本领，单位是焦耳（J）。功率是能量转移的速率，单位是瓦特（W），1 W = 1 J/s。功率说明能量转移得有多快，而不是转移了多少能量。
P = E ÷ t
where P is power in watts, E is energy transferred in joules and t is time in seconds. A 3 kW kettle and a 1 kW kettle both need about 300 000 J to boil the same amount of water, but the 3 kW kettle transfers that energy three times faster.
其中 P 是功率（瓦），E 是转移的能量（焦），t 是时间（秒）。3 kW 和 1 kW 的电水壶烧开同样多的水都需要约 300 000 J 的能量，但 3 kW 的水壶能量转移速度快三倍。
Exam trap: 'more powerful' does not mean 'uses more energy' and is usually expressed as a percentage: efficiency = (useful output ÷ total input) × 100%.
考试陷阱：“功率更大”并不等于“消耗更多能量”。同时要记住，效率是比较有用能量输出与总能量输入，通常用百分数表示：效率 =（有用输出 ÷ 总输入）× 100%。
4. Heat vs Temperature | 热量与温度
Temperature is a measure of the average kinetic energy of the particles in a substance. It is measured in degrees Celsius (°C) or kelvin (K), and it does not depend on how much of the substance you have.
温度是物质中粒子平均动能的量度。它的单位是摄氏度（°C）或开尔文（K），并且与物质的多少无关。
Thermal energy (often called 'heat') is the total internal energy stored or transferred, measured in joules (J). It does depend on mass. A cup of water and a bath of water can both be at 40 °C, but the bath stores far more thermal energy.
热能（常被称为“热量”）是储存或转移的总内能，单位是焦耳（J）。它与质量有关。一杯水和一浴缸水都可以是 40 °C，但浴缸储存的热能多得多。
E = m × c × Δθ
eat capacity in J/kg°C and Δθ is the temperature change in °C. For water, c = 4200 J/kg°C.
式中 E 是转移的能量（焦），m 是质量（千克），c 是比热容（J/kg°C），Δθ 是温度变化（°C）。水的比热容 c = 4200 J/kg°C。
Exam trap: never write 'heat rises' when you mean 'temperature rises', and never confuse the total energy transferred with the temperature change. A large mass needs more energy for the same temperature rise.
考试陷阱：想说“温度升高”时不要写成“热量升高”；也不要把转移的总能量与温度变化混为一谈。质量越大，升高相同温度所需能量越多。
5. Current vs Voltage | 电流与电压
Electric current is the rate of flow of electric charge, measured in amperes (A) with an ammeter connected in series. Charge itself is measured in coulombs (C).
电流是电荷流动的速率，用安培（A）作单位，用串联在电路中的电流表测量。电荷本身用库仑（C）作单位。
Q = I × t and V = W ÷ Q
Potential difference (voltage) is the energy transferred per unit charge, measured in volts (V) with a voltmeter connected in parallel across a component. One volt means one joule of energy is transferred per coulomb of charge.
电位差（电压）是每单位电荷所转移的能量，用伏特（V）作单位，用并联在元件两端的电压表测量。1 伏特意味着每库仑电荷转移 1 焦耳能量。
Exam trap: current is not 'used up' as it goes round a series circuit — it is the same at every point. What is shared in a series circuit is the voltage. In a parallel circuit the voltage is the same across each branch, while the current splits.
考试陷阱：在串联电路中电流并不会被“用掉”——电路各点电流相同。串联电路中被分配的是电压。并联电路中各支路电压相同，而电流会分流。
6. Atom, Ion and Isotope | 原子、离子与同位素
The atomic number (proton number) is the number of protons in the nucleus, and it defines which element an atom is. The mass number is the number of protons plus the number of neutrons in the nucleus.
原子序数（质子数）是原子核中质子的数目，它决定了一个原子属于哪种元素。质量数是原子核中质子数与中子数之和。
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Because they have the same electron arrangement, isotopes have identical chemical properties, but slightly different physical properties such as density and mass.
同位素是同一种元素的原子，质子数相同但中子数不同。由于电子排布相同，同位素的化学性质完全相同，但物理性质（如密度、质量）略有差异。
An ion is a charged particle formed when an atom loses or gains electrons. Metals lose electrons to form positive ions (Na⁺, Mg²⁺), while non-metals gain electrons to form negative ions (Cl⁻, O²⁻).
离子是原子失去或得到电子后形成的带电粒子。金属失去电子形成正离子（Na⁺、Mg²⁺），非金属得到电子形成负离子（Cl⁻、O²⁻）。
Exam trap: when explaining why isotopes react identically, you must refer to electrons, not neutrons. When explaining why ions and atoms of the same element differ, refer to the number of electrons, not to the nucleus.
考试陷阱：解释同位素化学性质相同时，必须说“电子”，不能说是中子。解释同种元素的离子与原子不同时，要说电子数目不同，而不是原子核不同。
7. Element, Compound and Mixture | 元素、化合物与混合物
An element contains only one type of atom and cannot be broken down chemically into anything simpler. A compound contains two or more different elements chemically bonded together in fixed proportions, for example water (H₂O) or carbon dioxide (CO₂).
元素只含一种原子，不能通过化学方法分解成更简单的物质。化合物由两种或更多不同元素以固定比例化学结合而成，例如水（H₂O）或二氧化碳（CO₂）。
A mixture contains two or more substances that are not chemically bonded, so the proportions can vary and the components can usually be separated by physical methods such as filtration, distillation or chromatography.
混合物由两种或更多没有化学结合的物质组成，因此比例可以变化，各成分通常可用过滤、蒸馏或色谱等物理方法分离。
Exam trap: alloys such as brass and steel are mixtures, not compounds, because the metal atoms are not chemically bonded in fixed ratios. Air is a mixture of gases; the ratio of nitrogen to oxygen is roughly 78:21 but not fixed by a chemical formula.
考试陷阱：黄铜、钢等合金是混合物而非化合物，因为其中的金属原子并没有以固定比例化学结合。空气是气体混合物；氮与氧的比例约为 78:21，但不是由化学式固定的。
8. Exothermic vs Endothermic | 放热反应与吸热反应
An exothermic reaction transfers energy to the surroundings, so the temperature of the surroundings rises. Examples include combustion, neutralisation and respiration. The energy level diagram shows the products lower than the reactants.
放热反应向周围环境释放能量，因此环境温度升高。例如燃烧、中和反应和呼吸作用。能量变化图中产物能级低于反应物能级。
An endothermic reaction takes in energy from the surroundings, so the temperature of the surroundings falls. Examples include thermal decomposition of calcium carbonate and photosynthesis. The products are at a higher energy level than the reactants.
吸热反应从周围环境吸收能量，因此环境温度降低。例如碳酸钙的热分解和光合作用。产物能级高于反应物能级。
At a particle level, bond breaking is endothermic and bond making is exothermic. The overall energy change of a reaction is the difference between the energy needed to break bonds in the reactants and the energy released when bonds form in the products.
从粒子层面看，断键吸热，成键放热。反应的总能量变化等于断裂反应物中化学键所需能量与形成产物中化学键所释放能量之差。
ΔH = energy in (bonds broken) − energy out (bonds formed)
Exam trap: catalysis does not change whether a reaction is exothermic or endothermic, and it does not change the overall energy change. It only lowers the activation energy, allowing more particles to react per unit time.
考试陷阱：催化剂不改变反应是放热还是吸热，也不改变总能量变化。它只是降低活化能，使单位时间内更多粒子能够反应。
9. Acid vs Alkali, Strong vs Weak | 酸与碱、强酸与弱酸
An acid is a proton (H⁺) donor and has a pH below 7. An alkali is a soluble base that produces hydroxide ions (OH⁻) in solution and has a pH above 7. Neutralisation can be summarised as:
酸是质子（H⁺）给体，pH 小于 7。碱是可溶性碱，在溶液中产生氢氧根离子（OH⁻），pH 大于 7。中和反应可表示为：
H⁺ + OH⁻ → H₂O
The strength of an acid refers to how completely it ionises in water. A strong acid such as hydrochloric acid ionises completely, while a weak acid such as ethanoic acid ionises only partially, setting up an equilibrium. This is different from concentration, which is how much acid is dissolved per unit volume.
酸的强度指的是它在水中电离的完全程度。盐酸等强酸完全电离，而乙酸等弱酸只部分电离，形成平衡。这与浓度不同，浓度指的是单位体积中溶解了多少酸。
Exam trap: 'dilute' is not the opposite of 'strong'. You can have a dilute solution of a strong acid (low concentration, fully ionised) or a concentrated solution of a weak acid (high concentration, partially ionised). Also remember that pH 1 has ten times the H⁺ concentration of pH 2.
考试陷阱：“稀”不是“强”的反义词。强酸可以很稀（浓度低但完全电离），弱酸也可以很浓（浓度高但部分电离）。另外要记住，pH 1 的 H⁺ 浓度是 pH 2 的十倍。
10. Diffusion, Osmosis and Active Transport | 扩散、渗透与主动运输
Diffusion is the passive movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient. It happens in gases and liquids, requires no energy from the cell, and continues until the concentrations are equal.
扩散是粒子从高浓度区域向低浓度区域的被动运动，顺着浓度梯度进行。它发生在气体和液体中，不需要细胞提供能量，直到浓度相等才停止。
Osmosis is a special case of diffusion: it is the movement of water molecules only, through a partially permeable membrane, from a region of higher water potential (more dilute solution) to a region of lower water potential (more concentrated solution).
渗透是扩散的一种特殊情况：只有水分子通过半透膜，从水势较高处（较稀的溶液）移动到水势较低处（较浓的溶液）。
Active transport moves substances against a concentration gradient, from low to high concentration. It requires energy from respiration (ATP) and carrier proteins in the cell membrane. In humans it is used in the gut and in the kidney tubules; in plants it is used to take up mineral ions from the soil.
主动运输把物质逆浓度梯度运输，从低浓度运向高浓度。它需要呼吸作用提供的能量（ATP）以及细胞膜上的载体蛋白。人体中用于肠道和肾小管，植物中用于从土壤吸收矿质离子。
Exam trap: osmosis is about water only. If a WJEC question describes sugar or mineral ions moving, the answer is diffusion or active transport, never osmosis.
考试陷阱：渗透只涉及水。如果 WJEC 题目描述的是糖或矿质离子移动，答案应为扩散或主动运输，绝不能写渗透。
11. Breathing vs Respiration | 呼吸运动与呼吸作用
Breathing (ventilation) is a mechanical process: the movement of air into and out of the lungs, driven by the diaphragm and intercostal muscles. It involves no enzymes and no chemical reaction.
呼吸运动（通气）是机械过程：空气在肺内进出，由膈肌和肋间肌驱动。它不涉及酶，也不涉及化学反应。
Respiration is a chemical process that takes place inside cells. It is controlled by enzymes and releases energy from glucose for processes such as muscle contraction, active transport and keeping warm.
呼吸作用是发生在细胞内的化学过程，由酶控制，从葡萄糖中释放能量，供肌肉收缩、主动运输和维持体温等过程使用。
aerobic: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy)
anaerobic (muscle): C₆H₁₂O₆ → 2C₃H₆O₃ (+ energy)
Aerobic respiration needs oxygen and releases much more energy per glucose molecule than anaerobic respiration, which produces lactic acid in muscle cells and ethanol plus carbon dioxide in yeast.
有氧呼吸需要氧气，每分子葡萄糖释放的能量远多于无氧呼吸；无氧呼吸在肌细胞中产生乳酸，在酵母中产生乙醇和二氧化碳。
Exam trap: anaerobic respiration in humans does not produce carbon dioxide or ethanol. Also, the oxygen debt is the extra oxygen needed after exercise to break down the lactic acid that has built up.
考试陷阱：人体的无氧呼吸不产生二氧化碳，也不产生乙醇。另外，氧债是运动后为分解积累的乳酸而需要的额外氧气。
12. Photosynthesis vs Respiration | 光合作用与呼吸作用
Photosynthesis is an endothermic process that takes place in the chloroplasts of plant cells. It uses light energy to convert carbon dioxide and water into glucose and oxygen. It only happens in the light.
光合作用是吸热过程，发生在植物细胞的叶绿体中。它利用光能把二氧化碳和水转化为葡萄糖和氧气，只能在有光时进行。
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Respiration is an exothermic process that takes place in the mitochondria. It releases energy from glucose, and in plants it happens twenty-four hours a day, in both light and darkness.
呼吸作用是放热过程，发生在线粒体中。它从葡萄糖中释放能量，在植物体内一天二十四小时都在进行，无论白天还是黑夜。
Exam trap: plants respire all the time, so at night the net oxygen release is zero and carbon dioxide is released. In daytime experiments, the net gas exchange you measure is the balance between photosynthesis and respiration, not photosynthesis alone.
考试陷阱：植物始终在呼吸，所以夜间净氧气释放量为零，反而释放二氧化碳。在白天实验中，你测到的净气体交换是光合作用与呼吸作用相互抵消后的结果，而不只是光合作用。
Exam trap: do not write that plants 'breathe in' carbon dioxide. Plants take in carbon dioxide as a reactant for photosynthesis through the stomata; oxygen uptake for respiration is a separate process.
考试陷阱：不要写植物“吸入”二氧化碳来呼吸。植物通过气孔吸收二氧化碳是作为光合作用的反应物；为呼吸作用摄取氧气是另一个独立过程。
13. Using Precise Terminology in WJEC Answers | 在 WJEC 答题中使用精确术语
WJEC mark schemes award marks for specific words. If the mark scheme says 'water potential' or 'gravitational
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