A-Level WJEC Biology: Common Misconceptions | A-Level WJEC生物：常见误区

📚 A-Level WJEC Biology: Common Misconceptions | A-Level WJEC生物：常见误区

Many A-Level Biology candidates sitting the WJEC examinations lose marks not because they lack knowledge, but because they hold onto stubborn misconceptions that distort their understanding of key processes. This article identifies and clarifies the most prevalent errors, helping you avoid these pitfalls and write accurate, mark-scheme-friendly answers.

许多参加 WJEC A-Level 生物考试的学生之所以丢分，并非知识匮乏，而是抱持顽固的错误观念，扭曲了对关键过程的理解。本文梳理并澄清最普遍的错误，助你避开这些陷阱，写出符合评分标准的精准答案。

1. Enzyme Activity and Temperature | 酶活性与温度

A widespread misconception is that enzyme activity increases linearly with temperature up to the denaturation point, after which the enzyme abruptly stops working. In reality, as temperature rises, kinetic energy increases, leading to more frequent collisions between enzyme and substrate, so the rate of reaction rises to an optimum (often around 40 °C for human enzymes). Beyond this optimum, the increased vibration breaks hydrogen bonds and ionic interactions that maintain the enzyme’s tertiary structure, causing the active site to change shape and lose its complementary fit to the substrate. The enzyme is then denatured, and the reaction rate falls sharply – but not to zero instantly. At very low temperatures the enzyme is not denatured; activity is simply very slow because molecules have low kinetic energy.

一个普遍误解是酶活性随温度线性上升，直至变性点，之后酶突然停止工作。实际上，随着温度升高，动能增加，酶与底物碰撞更频繁，反应速率上升到最适温度（人类酶约 40 °C）。超过最适温度后，增加的振动破坏了维持酶三级结构的氢键和离子键，使活性部位形状改变，不再与底物互补。酶变性，反应速率急剧下降——但不是瞬间降为零。在极低温度下酶并未变性；只是分子动能低因而反应很慢。

2. pH and Enzyme Function | pH 与酶功能

Students often think that pH only alters the rate temporarily, like temperature, and that returning to the optimum pH fully restores activity. In fact, changes in pH affect the ionisation of amino acid side chains at the active site, disrupting ionic bonds that stabilise the tertiary structure. If the pH shift is small, the effect may be reversible, but extreme pH values can cause irreversible denaturation, just like high temperature. WJEC mark schemes expect candidates to distinguish between reversible inhibition at sub-optimal pH and irreversible denaturation at extreme pH.

学生常认为 pH 仅像温度一样暂时改变速率，回到最适 pH 就能完全恢复活性。实际上，pH 变化影响活性部位氨基酸侧链的电离，破坏稳定三级结构的离子键。pH 变化较小时效应可能可逆，但极端 pH 可导致不可逆变性与高温情况类似。WJEC 评分方案期望考生区分亚适 pH 下的可逆抑制和极端 pH 下的不可逆变性。

3. Anaerobic Respiration in Plants and Animals | 植物和动物的无氧呼吸

A very common error is to state that anaerobic respiration always produces lactic acid. In WJEC exams, you must specify the organism. Mammalian muscle cells convert pyruvate to lactate using lactate dehydrogenase, regenerating NAD⁺. In contrast, plants and yeast produce ethanol and carbon dioxide (CO₂) via alcohol fermentation: pyruvate is decarboxylated to ethanal, which is then reduced to ethanol, regenerating NAD⁺. Confusing the two pathways loses marks.

一个非常常见的错误是说无氧呼吸总是产生乳酸。在 WJEC 考试中，你必须指明生物体。哺乳动物肌肉细胞利用乳酸脱氢酶将丙酮酸转化为乳酸，再生 NAD⁺。而植物和酵母通过酒精发酵产生乙醇和 CO₂：丙酮酸脱羧生成乙醛，然后被还原为乙醇，再生 NAD⁺。混淆这两条途径会失分。

4. The Light-Independent Reactions (Calvin Cycle) | 暗反应（卡尔文循环）

The term ‘light-independent reactions’ leads many students to believe they occur only at night. In fact, these reactions use the products of the light-dependent stage – ATP and reduced NADP (NADPH) – to fix CO₂ and synthesise triose phosphate. Provided ATP and NADPH are available, the Calvin cycle proceeds continuously during daylight. At night, when light reactions stop, the supply of ATP and NADPH dwindles, and the Calvin cycle gradually halts. Describing these as ‘dark reactions’ is misleading.

‘光不依赖反应’一词使许多学生误以为它们只在夜晚发生。实际上，这些反应利用光反应阶段的产物——ATP 和还原型 NADP (NADPH)——来固定 CO₂ 并合成磷酸三碳糖。只要有 ATP 和 NADPH，卡尔文循环在白天持续进行。到了夜晚光反应停止，ATP 和 NADPH 供应枯竭，卡尔文循环逐渐停止。称其为’暗反应’具有误导性。

5. Dominant Alleles Are Not Always More Common | 显性等位基因并不总是更常见

Students often equate ‘dominant’ with ‘frequent’. In genetics, dominance describes the relationship between alleles: a dominant allele is expressed in the phenotype of a heterozygote. Its frequency in the population depends on mutation rates, selection pressures, genetic drift, and migration – not on dominance. For instance, Huntington’s disease is caused by a dominant allele yet is extremely rare. Conversely, blue eyes (recessive) can be common in some populations. WJEC questions may ask for this distinction.

学生常将’显性’等同于’常见’。在遗传学中，显性描述的是等位基因间的关系：显性等位基因在杂合个体中表现出其性状。它在种群中的频率取决于突变率、选择压力、遗传漂变和迁移——而不是显性。例如亨廷顿病由显性等位基因引起却极为罕见。相反，蓝眼睛（隐性）在某些种群中可以很常见。WJEC 考题可能要求这一区分。

6. Natural Selection Misconception: ‘Use and Disuse’ | 自然选择误区：’用进废退’

A pre-Darwinian view that organisms ‘strive’ to adapt still creeps into A-Level answers. Evolution by natural selection requires heritable variation arising from random mutations and meiosis. Those individuals with phenotypes that give a reproductive advantage are more likely to survive and pass on alleles. There is no intentional adaptation. The phrase ‘the giraffe stretched its neck to reach leaves’ is incorrect; rather, giraffes with slightly longer necks had a survival advantage, and neck length gradually increased over generations.

一种拉马克式的观点——生物’努力’去适应——仍会出现在 A-Level 答案中。自然选择进化要求由随机突变和减数分裂产生的可遗传变异。那些具有生殖优势表型的个体更有可能存活并传递等位基因。不存在有目的的适应。’长颈鹿伸长了脖子去够树叶’是错误的；更确切的是，脖子稍长的长颈鹿拥有生存优势，世代间脖子长度逐渐增加。

7. Antibiotics Work Against Viruses | 抗生素对病毒有效

Many students still believe antibiotics can cure viral infections. Antibiotics target specific features of bacteria, such as cell wall synthesis (e.g. penicillin inhibits transpeptidase), 70S ribosomes, or DNA gyrase. Viruses lack these structures; they rely on host cell machinery. Using antibiotics for viral illnesses is not only ineffective but also contributes to antibiotic resistance. WJEC Biology expects you to explain why antibiotics do not affect viruses.

许多学生仍然相信抗生素能治疗病毒感染。抗生素针对细菌的特定特征，例如细胞壁合成（青霉素抑制转肽酶）、70S 核糖体或 DNA 旋转酶。病毒没有这些结构；它们依赖宿主细胞机器。用抗生素治疗病毒性疾病不仅无效，还会导致抗生素耐药性。WJEC 生物要求你解释为什么抗生素不影响病毒。

8. Mitosis vs. Meiosis: Chromosome Number | 有丝分裂与减数分裂：染色体数目

A common slip is saying meiosis produces two diploid daughter cells. Meiosis actually consists of two successive divisions (meiosis I and II) resulting in four haploid cells. During meiosis I, homologous chromosomes separate, halving the chromosome number. This is crucial for sexual reproduction, as fusion of gametes restores diploid number. Mitosis, on the other hand, produces two genetically identical diploid cells. Confusing the outcomes can cost marks in both essay and data-interpretation questions.

一个常见口误是说减数分裂产生两个二倍体子细胞。减数分裂实际上由两次连续分裂（减数 I 和 II）组成，产生四个单倍体细胞。在减数 I 中，同源染色体分离，染色体数目减半。这对有性生殖至关重要，因为配子融合会恢复二倍体数目。而有丝分裂产生两个遗传上相同的二倍体细胞。混淆两者结果会在论文和数据分析题中失分。

9. Action Potential is ‘All or Nothing’ | 动作电位是’全或无’的

Many learners think a stronger stimulus generates a bigger action potential. However, once threshold potential (about -55 mV) is reached, voltage-gated Na⁺ channels open, causing a rapid depolarisation to roughly +40 mV that does not vary with stimulus strength. The nervous system codes stimulus intensity by the frequency of action potentials. WJEC also requires understanding of the absolute refractory period, which ensures unidirectional propagation and limits maximum

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