📚 AS WJEC Biology: Common Misconceptions and How to Correct Them | AS WJEC 生物常见误区与纠正方法
The WJEC AS Biology course runs from biochemistry and cell structure through to transport, genetics and physiology, and it rewards precision above almost everything else. Many students lose marks not because they do not know the topic, but because a persistent misconception sits underneath their answer and quietly distorts it. This article collects the most common of those misconceptions, explains why they are wrong, and gives you the corrected version in the exact language WJEC mark schemes expect.
WJEC 的 AS 生物课程从生物化学、细胞结构一直延伸到物质运输、遗传学和生理学，它最看重的几乎就是表达的精确性。许多学生失分并不是因为不懂知识点，而是因为某个顽固的误区藏在答案底下，悄悄地把答案带偏了。本文汇总了最常见的这些误区，解释它们为什么错，并给出 WJEC 评分标准真正期待的正确表述。
1. Do Animal Cells Have a Cell Wall? | 动物细胞有细胞壁吗？
Many students assume that every cell is surrounded by a rigid cell wall, because the classic textbook diagram of a "generalised cell" is drawn as a neat rectangle. In reality, animal cells are bounded only by a cell membrane. A cell wall is an additional, non-living layer found outside the membrane in plants, fungi and most bacteria, and it is chemically different in each group.
许多学生认为所有细胞外面都有一层坚硬的细胞壁，因为教科书上经典的"通用细胞"示意图总是画成一个规整的矩形。事实上，动物细胞只由细胞膜包被。细胞壁是位于细胞膜之外的一层额外的、非生命的结构，存在于植物、真菌和大多数细菌中，而且各组成部分的化学成分完全不同。
| Organism | 生物类群 | Wall material | 细胞壁成分 |
| Plants 植物 | Cellulose 纤维素 |
| Fungi 真菌 | Chitin 几丁质 |
| Bacteria 细菌 | Peptidoglycan (murein) 肽聚糖 |
| Animals 动物 | None 无 |
The correction matters for three reasons. First, the wall is fully permeable, so it plays no part in selective uptake of substances; that job belongs to the cell membrane. Second, animal cells obtain structural support from the cytoskeleton and the extracellular matrix instead of a wall. Third, the wall has a real function in plants: it resists the turgor pressure that builds up as water enters, preventing the cell from bursting.
这个纠正之所以重要，有三个原因。第一，细胞壁是完全可渗透的，因此它不参与物质的选择性吸收，那是细胞膜的职责。第二，动物细胞的结构支撑来自细胞骨架和细胞外基质，而不是细胞壁。第三，细胞壁在植物中有实际功能：它抵抗水分进入后产生的膨压，防止细胞胀破。
Exam tip: never write "animal cells have a thin cell wall". If a question asks about support in animal cells, refer to the cytoskeleton; if it asks about support in plant cells, refer to the cell wall and turgor.
考试提示：绝不要写"动物细胞有一层薄的细胞壁"。如果题目问动物细胞的支撑，答细胞骨架；如果问植物细胞的支撑，答细胞壁与膨压。
2. Is Enzyme Denaturation Reversible? | 酶变性是可逆的吗？
Denaturation is the loss of an enzyme's tertiary structure, so that the precise shape of the active site is destroyed and the substrate can no longer bind to form enzyme-substrate complexes. Because hydrogen bonds and ionic bonds holding the folded chain in place are broken, the process is normally irreversible: the chain cannot spontaneously refold into the exact original shape once it has unfolded.
变性是指酶的三级结构丧失，活性位点的精确形状被破坏，底物不再能与它结合形成酶-底物复合物。由于维持多肽链折叠的氢键和离子键被破坏，这一过程通常不可逆：一旦链展开，就无法自发地重新折叠回原来完全相同的形状。
What is reversible is quite different. Lowering the temperature slows an enzyme down by reducing the kinetic energy of the molecules, so fewer successful collisions occur and fewer enzyme-substrate complexes form. The enzyme is inactive but not denatured, and activity returns on warming. Competitive and non-competitive inhibition are also reversible, whereas extreme pH
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