📚 IB and CCEA Science: Common Misconceptions | IB CCEA 科学：常见误区
Science examinations in both IB and CCEA specifications test not only factual recall but also the ability to apply correct conceptual models. Yet year after year, assessors report the same persistent misunderstandings costing students valuable marks. From Newtonian mechanics to the nature of chemical equilibrium, these misconceptions often stem from intuitive but incorrect everyday experiences or oversimplified earlier teaching. This article unpacks the most frequent pitfalls, explains the accurate science behind each topic, and offers strategies to avoid them in your IB or CCEA exams.
无论是 IB 还是 CCEA 的科学考试，考查的都不只是事实背诵，更是对正确概念模型的运用能力。然而年复一年，考官报告都指出，一些根深蒂固的错误理解让学生丢掉了宝贵的分数。从牛顿力学到化学平衡的本质，这些误区通常源于日常直觉（但错误）的经验，或是先前教学中的过度简化。本文拆解最高频的错误观念，阐释每个主题背后的准确科学，并提供在 IB 或 CCEA 考试中避免入坑的策略。
1. Force and Motion: “Constant Force Means Constant Velocity” | 力与运动误区：恒力等于恒定速度吗？
Many students believe that a continuous force is required to keep an object moving at constant velocity. This Aristotelian notion is reinforced by everyday experience, such as needing to push a shopping trolley to maintain speed on rough ground. According to Newton’s first law, however, an object will remain at rest or in uniform motion in a straight line unless acted upon by a resultant external force. A constant velocity implies zero net force; the forces are balanced.
很多学生误以为维持物体匀速运动需要持续施加一个力。这种亚里士多德式的观念被日常经验强化，比如在粗糙地面上必须持续推动购物车才能保持速度。但根据牛顿第一定律，除非受到净外力，物体会保持静止或匀速直线运动状态。匀速运动意味着合外力为零，力是平衡的。
In IB Physics and CCEA AS Physics, questions often ask about the forces acting on a car moving at constant speed on a straight road. The correct answer is that the driving force equals the resistive forces, resulting in zero net force. A common error is to say the driving force must be greater than resistance to keep it moving.
在 IB 物理和 CCEA AS 物理中，题目常问一辆汽车在平直公路上匀速行驶时受哪些力。正确答案是驱动力等于阻力，合外力为零。常见错误是说驱动力必须大于阻力才能让它前进。
Furthermore, confusion between velocity and acceleration causes problems with circular motion: an object moving in a circular path at constant speed has a changing velocity and experiences a centripetal acceleration towards the centre. The net force is not zero; it provides the centripetal force.
此外，混淆速度与加速度还会在圆周运动中引发问题：物体以恒定速率做圆周运动时，速度方向不断变化，具有指向圆心的向心加速度。合外力不为零，它提供向心力。
2. Energy: “Energy Is Used Up” | 能量误区：能量被“消耗”了
A pervasive misconception is that energy disappears after it has been ‘used’. Students often state that energy is “used up” in a lamp or a battery “runs out” of energy. The principle of conservation of energy states that energy cannot be created or destroyed, only transferred, stored or dissipated in less useful forms.
一个非常普遍的误区是认为能量在被“用掉”后就消失了。学生常说灯“用完了”能量，或电池“耗尽”了能量。能量守恒定律指出，能量不会凭空产生或消失，只能被转移、储存或转化为不那么有用的形式耗散掉。
In IB and CCEA exams, answers must reflect that electrical devices transfer energy from stored chemical potential (in a battery) into light and thermal energy, with the total amount conserved. The energy is often dissipated as thermal energy to the surroundings, becoming less available to do useful work but not destroyed.
在 IB 和 CCEA 考试中，答案必须反映出电子设备将电池中储存的化学势能转化为光能和热能，总能量守恒。能量通常以热能的形式耗散到周围环境，变得较难用以做有用功，但并非被消灭。
A linked misunderstanding involves the concept of ‘heat’ as a substance. Heat is not a fluid contained in bodies but a process of energy transfer due to temperature difference. Use the term ‘thermal energy’ carefully. In IB, distinguishing between thermal energy, temperature and internal energy is essential for topic 3.
一个相关联的误区是把“热”当成一种物质。热并非物体中含有的流体，而是由于温度差而发生的能量传递过程。要谨慎使用“热能”这一术语。在 IB 课程（主题 3）中，区分热能、温度和內能至关重要。
3. Chemical Equilibrium: “Reactions Stop at Equilibrium” | 化学平衡误区：平衡时反应停止
Many learners interpret a chemical equilibrium as a static situation where reactants and products have stopped reacting. In reality, equilibrium is dynamic: the forward and reverse reactions continue to occur simultaneously at equal rates, so the macroscopic concentrations remain constant. A classic demonstration is adding a few drops of an iodine-131 solution to a saturated lead iodide equilibrium; the radioactive iodine soon appears in both solid and solution phases, proving that dissolution and precipitation are ongoing.
许多学习者将化学平衡解释为一种静止状态，即反应物和生成物都停止反应。实际上，平衡是动态的：正反应和逆反应同时以相等的速率进行，因此宏观浓度保持恒定。一个经典演示是向饱和碘化铅平衡体系中加入几滴碘-131 溶液；放射性碘很快出现在固相和溶液相中，证明溶解和沉淀都在不断进行。
CCEA AS Chemistry and IB HL Chemistry both require students to apply Le Chatelier’s Principle correctly. A common error is to claim that a catalyst shifts the position of equilibrium or increases the yield of products. Catalysts only lower the activation energy for both forward and reverse reactions equally, so they increase the rate at which equilibrium is reached without altering the equilibrium position.
CCEA AS 化学和 IB HL 化学都要求学生正确应用勒夏特列原理。一个常见错误是声称催化剂能移动平衡位置或提高产物产率。催化剂只是同等程度降低正逆反应的活化能，因此提高达到平衡的速率，但不改变平衡位置。
Another subtle point: changes in pressure only affect an equilibrium if there is a difference in the number of gas molecules on each side, and adding an inert gas at constant volume does not shift the equilibrium because partial pressures of reactants and products remain unchanged.
另一个微妙之处：压强变化只有当反应前后气体分子总数不同时才会影响平衡，而在恒容条件下加入惰性气体不会移动平衡，因为反应物和产物的分压不变。
4. Genetics: “Dominant Alleles Are More Common” | 遗传学误区：显性等位基因更常见
A deeply embedded misconception is that a dominant allele is always more frequent in a population than a recessive one. Dominance refers to the phenotypic expression in a heterozygote, not to allele frequency. For example, the allele for Huntington’s disease is dominant but extremely rare, while the allele for O blood type is recessive yet very common in many populations.
一个根深蒂固的误解是：显性等位基因在群体中总比隐性等位基因更常见。显性指的是杂合子中的表型表达，而与等位基因频率无关。例如，亨廷顿病的等位基因是显性的，但极为罕见；而 O 血型的等位基因为隐性，在许多人群中却十分常见。
IB Biology Topic 3 and CCEA AS Biology both examine inheritance patterns. Students must avoid conflating “dominant” with “better” or “more frequent”. Natural selection acts on phenotypes, not on dominance labels, and can maintain deleterious recessive alleles at low frequencies in carrier heterozygotes.
IB 生物主题 3 和 CCEA AS 生物都考查遗传模式。学生必须避免将“显性”与“更好”或“更频繁”混为一谈。自然选择作用于表型，而非显隐性标签，并能将有害隐性等位基因以携带者杂合子的形式维持在低频率。
When solving pedigree problems, do not assume an affected parent passes a dominant condition to all offspring; expression probability depends on whether the trait is autosomal dominant, autosomal recessive, or sex-linked.
在解系谱图问题时，不要认定患病亲本会把常染色体显性性状传给所有后代；表达概率取决于该性状是常染色体显性、常染色体隐性还是伴性遗传。
5. Electricity: “Electrons Travel at the Speed of Light in Wires” | 电路误区：电子以光速在导线中运动
It is common to hear that electricity moves at the speed of light. While electromagnetic signals propagate through a circuit at speeds approaching the speed of light, individual free electrons drift very slowly, with typical drift velocities of the order of 10⁻⁴ m s⁻¹ in a copper wire. The signal speed is due to the electric field set up almost instantaneously throughout the circuit, pushing electrons along like a chain of collisions.
人们常听到电以光速运动。尽管电磁信号以接近光速的速度在电路中传播，但单个自由电子的移动非常缓慢，在铜导线中典型的漂移速度约 10⁻⁴ m s⁻¹。信号速度源于电场几乎瞬间在整个电路中建立，像推倒多米诺骨牌一样推动电子碰撞前行。
IB Physics Topic 5 and CCEA Physics A-Level both require a precise distinction between current, potential difference and resistance. The definition of current (I = Δq / Δt) describes the net rate of flow of charge past a point. Misunderstanding drift velocity can lead to errors in explaining the effect of temperature on resistance: in metals, increased temperature causes more intense lattice vibrations, which increases the frequency of collisions and reduces the average drift velocity, hence resistance increases.
IB 物理主题 5 和 CCEA 物理 A-Level 都要求精确区分电流、电势差和电阻。电流的定义（I = Δq / Δt）描述电荷通过某点的净流动速率。误解漂移速度会导致在解释温度对电阻的影响时出错：在金属中，温度升高使晶格振动加剧，电子碰撞频率增加，平均漂移速度减小，因此电阻增大。
Another classic pitfall is assuming current is “used up” in a series circuit. Current is conserved throughout a single-loop series circuit; it is the same at all points.
另一个经典陷阱是认为串联电路中电流被“用完”了。电流在单回路串联电路中处处相等，是守恒的。
6. Evolution: “Humans Evolved from Chimpanzees” | 进化误区：人类从黑猩猩进化而来
Perhaps the most repeated misconception about evolution is that humans descended from modern chimpanzees or monkeys. Evolutionary theory states that humans and chimpanzees share a common ancestor that lived roughly 6–7 million years ago. Both lineages have evolved independently since that divergence; chimpanzees are our evolutionary cousins, not our ancestors.
关于进化，也许被重复最多的误解就是人类由现代黑猩猩或猴子演变而来。进化论指出，人类和黑猩猩共享一个生活在大约 600 至 700 万年前的共同祖先。自分开以来，两个支系一直独立进化；黑猩猩是我们的演化表亲，而非祖先。
IB Biology Topic 5 and CCEA Option units stress the evidence for evolution, including comparative anatomy, molecular phylogeny and fossil records. Exam markers penalise statements suggesting a linear progression from ape to human. Instead, refer to a branching evolutionary tree with many extinct hominin species.
IB 生物主题 5 和 CCEA 选修单元都强调进化证据，包括比较解剖学、分子系统发育和化石记录。考官会扣掉暗示从猿到人线性进化的表述分。应代之以分支状的进化树，树上有许多已灭绝的人族物种。
Natural selection does not “plan” or “cause” mutations to meet an environmental need. Mutations occur randomly; if a variant enhances fitness in a given environment, it increases in frequency over generations. Avoid teleological language such as “the giraffe grew a long neck to reach high leaves”.
自然选择不会“计划”或“引起”突变来满足环境需求。突变随机发生；若某个变异在特定环境中提高了适应度，它就会在世代中增加频率。避免使用目的论语言，例如“长颈鹿为了吃到高处树叶而长出了长脖子”。
7. Cell Biology: “Mitochondria Produce Energy” | 细胞误区：线粒体“制造”能量
Textbooks and teachers often say “mitochondria are the powerhouses of the cell that produce energy”. This phrasing leads students to think energy is generated inside mitochondria, violating the law of conservation of energy. Mitochondria actually convert chemical energy stored in glucose into ATP through cellular respiration. Energy is transferred, not created.
教科书和老师常说“线粒体是细胞的能量工厂，生产能量”。这种表述让学生以为能量在线粒体内被创造，违背能量守恒定律。线粒体实际上通过细胞呼吸将储存在葡萄糖中的化学能转化为 ATP。能量被转移，而非创造。
In IB Biology HL Topic 2.8 and 8.2, as well as CCEA A-Level Biology, precise language is rewarded. Write “mitochondria transfer energy from organic molecules to ATP” or “sites of aerobic respiration where ATP is synthesised”. Also clarify that ATP is an energy carrier molecule, not a long-term energy store.
在 IB 生物 HL 主题 2.8 和 8.2 及 CCEA A-Level 生物中，精确用词能得分。应写“线粒体将有机分子中的能量转移到 ATP”或“有氧呼吸进行处，在此合成 ATP”。还要说明 ATP 是能量载体分子，不是长期储能物质。
Another related confusion is between cell wall and cell membrane. Plant, fungal and bacterial cells have a cell wall external to the cell membrane, which provides structural support, but the membrane controls entry and exit of substances.
另一个相关的混淆是细胞壁和细胞膜。植物、真菌和细菌细胞在细胞膜外还有细胞壁，提供结构支撑，但控制物质进出的是细胞膜。
8. Experimental Design: “More Data Always Improves Accuracy” | 实验设计误区：数据越多越准确
In IB Internal Assessments and CCEA practical assessments, a subtle yet critical distinction must be made between accuracy, precision and reliability. Many students believe that taking a larger number of readings will automatically increase accuracy. Precision relates to the scatter of repeated measurements (reduced by increasing sample size). Accuracy relates to how close a measurement is to the true value, which depends on eliminating systematic errors.
在 IB 内部评估和 CCEA 实验评估中，必须敏锐区分准确度、精确度和可靠性。很多学生以为增加读数次数会自动提高准确度。精确度关乎重复测量的离散程度（通过增加样本量来提升），而准确度关乎测量值离真值多近，这取决于消除系统误差。
Repeating a measurement many times improves the reliability and can help identify random errors, but if the apparatus is not calibrated or a zero error exists, accuracy remains poor. A student using a ruler with a worn end will get precise but inaccurate results even with 100 trials.
多次重复测量能提高可靠性，帮助发现随机误差，但若仪器未经校准或存在零误差，准确度依然差。一个使用了端头磨损的直尺的学生，即使做 100 次试验，结果也只能是精确而不准确。
IB science also emphasises that error bars on graphs represent the range or standard deviation of repeated measurements, not the absolute uncertainty of a single reading. Overlap of error bars indicates that a difference may not be statistically significant.
IB 科学还强调，图表上的误差线代表重复测量的范围或标准差，而非单次读数的绝对不确定度。误差线重叠表明差异可能不具有统计显著性。
9. Waves: “Sound Cannot Travel Without Air” | 波误区：没有空气声音就不能传播
Students often generalise that sound requires air to travel because humans normally perceive sound transmitted through air. Sound is a mechanical longitudinal wave that can propagate through any elastic medium—solids, liquids and gases. In fact, sound travels faster in solids than in air because particles are closer together, transmitting vibrations more rapidly.
学生常泛化地认为声音需要空气才能传播，因为人类通常感知到的是经空气传来的声音。声是机械纵波，可以在任何弹性介质中传播——固体、液体和气体。实际上，声音在固体中比在空气中传播更快，因为粒子间距更近，能更迅速地传递振动。
IB Physics Topic 4 and CCEA waves content require knowledge that sound cannot travel through a vacuum, but a common exam trick is to suggest that it can only travel through air. A bell jar experiment with a ringing bell shows no sound when air is removed, but if the bell were placed directly on the jar’s wall, vibrations could still be detected via the solid container.
IB 物理主题 4 和 CCEA 波的内容需要知道声音无法在真空中传播，但一个常见考题陷阱是暗示声音只能在空气中传播。玻璃罩闹铃实验表明抽走空气后听不到声音，但若闹铃直接接触罩壁，振动仍能通过固体容器被探测到。
Another wave misconception is that the frequency of a wave changes when it passes from one medium to another. In refraction, the speed and wavelength may change, but frequency remains constant as determined by the source.
另一个波的误区是波从一种介质进入另一种介质时频率会改变。在折射中，波速和波长可能改变，但频率由波源决定，保持不变。
10. Climate and Atmosphere: “Ozone Hole Causes Global Warming” | 大气与气候误区：臭氧层空洞导致全球变暖
A surprisingly persistent confusion exists between the depletion of stratospheric ozone and the enhanced greenhouse effect. Ozone depletion, primarily by CFCs, leads to increased levels of harmful ultraviolet radiation reaching Earth’s surface but does not directly trap outgoing longwave radiation. Global warming is caused by the accumulation of greenhouse gases like carbon dioxide, methane and water vapour, which absorb and re-radiate infrared radiation.
一个令人惊讶的持续混淆存在于平流层臭氧损耗和增强的温室效应之间。臭氧层损耗（主要由氯氟碳化物造成）导致到达地表的有害紫外线增多，但并不直接截获向外的高能长波辐射。全球变暖源于二氧化碳、甲烷和水蒸气等温室气体的累积，它们吸收并重新辐射红外辐射。
CCEA AS Environmental Science and IB Environmental Systems and Societies both highlight this distinction. It is wrong to suggest that the Kyoto Protocol addressed the ozone hole; the Montreal Protocol tackled CFCs to protect the ozone layer. Climate and ozone are separate global issues that interact only indirectly.
CCEA AS 环境科学和 IB 环境系统与社会都强调这一区别。声称《京都议定书》处理了臭氧层空洞是错误的；《蒙特利尔议定书》专门针对 CFCs 以保护臭氧层。气候与臭氧是独立的全球问题，仅间接地相互影响。
In addition, students confuse local air pollution (smog, acid rain) with global climate change. Acid rain is caused by sulfur dioxide and nitrogen oxides dissolving in water vapour, whereas the greenhouse effect is a necessary natural phenomenon made excessive by human emissions.
此外，学生常把局地空气污染（雾霾、酸雨）与全球气候变化混为一谈。酸雨由二氧化硫和氮氧化物溶于水蒸气引起，而温室效应本身是必要的自然现象，因人类排放而增强。
11. Atomic Structure: “Electrons Orbit the Nucleus Like Planets” | 原子结构误区：电子如行星般绕核运转
The planetary model of the atom, though historically important, is a major conceptual stumbling block. Electrons do not follow defined circular orbits; instead, they exist in three-dimensional regions called orbitals, which describe a probability distribution of where an electron is likely to be found. This quantum mechanical model is required for IB Chemistry Topic 2 and CCEA AS level explanations of ionisation energies and bonding.
原子的行星模型尽管在历史上很重要，却是一个主要的概念绊脚石。电子并不沿固定的圆轨道运行，而是存在于称为轨道的三维区域中，这些轨道描述了电子出现的概率分布。IB 化学主题 2 和 CCEA AS 水平对电离能和化学键的解释需要这种量子力学模型。
When explaining trends in first ionisation energy across a period, students must refer to increasing nuclear charge, similar shielding and a decrease in atomic radius, rather than painting a classical picture of electrons “moving further away” in fixed shells. The concept of orbitals (s, p, d) is essential for understanding the drop in ionisation energy from group 2 to group 3, and from group 5 to group 6.
在解释同一周期第一电离能的变化趋势时，学生必须提及核电荷增加、屏蔽效应相似和原子半径减小，而非用经典图像描述电子在固定壳层中“离核更远”。s, p, d 轨道的概念对理解第二族到第三族、第五族到第六族电离能的下降至关重要。
Another frequent misunderstanding is that atoms “want” full outer shells. This anthropomorphic language can hinder understanding of why atoms form bonds. Bonds form because they lower the overall energy of the system, not because atoms are individuals striving for an octet.
另一个频繁误解是原子“想要”填满最外层。这种拟人化语言会妨碍对原子成键原因的理解。化学键形成是因为它们降低了体系的总能量，而非原子个体在争取八隅体结构。
12. Genetics and Evolution Synthesis: “Acquired Characteristics Can Be Inherited” | 遗传与进化综合误区：获得性性状可遗传
Although Jean-Baptiste Lamarck’s theory of use and disuse has been largely rejected by modern biology, remnants of Lamarckian thinking persist in exam answers. Workouts that build muscles do not change the DNA passed to offspring; only changes in germline DNA (mutations) are heritable. This is a fundamental principle of neo-Darwinian evolution.
尽管拉马克的用进废退理论已被现代生物学基本否定，但拉马克思想的残余仍出现在考试答案中。锻炼增肌并不会改变传给后代的 DNA；只有生殖系 DNA 的改变（突变）是可遗传的。这是新达尔文主义进化的基本原则。
In both IB and CCEA, students must be able to contrast Darwinian and Lamarckian theory. For example, a giraffe that stretches its neck throughout its life to reach higher leaves does not pass a longer neck to its calves. Instead, ancestral giraffes with naturally slightly longer necks may have survived and reproduced better, shifting the population’s average neck length over many generations.
在 IB 和 CCEA 中，学生必须能够对比达尔文理论与拉马克理论。例如，一头长颈鹿一生拉长脖子够高处树叶，不会把更长的脖子遗传给幼崽。相反，那些天然脖子稍长的祖先可能有更高的存活和繁殖成功率，经多代使群体的平均颈长发生偏移。
Epigenetics represents a modern nuance where gene expression can be altered by environmental factors without changing the DNA sequence, but these changes are rarely passed on stably across multiple generations, and do not support Lamarckian inheritance in the classic sense.
表观遗传学代表了一个现代微妙领域，环境因素可以在不改变 DNA 序列的情况下改变基因表达，但这些变化很少能稳定地跨越多代传递，不支持经典意义上的拉马克式遗传。
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