A-Level Biology: Concept Clarifications | A-Level 生物：概念辨析

📚 A-Level Biology: Concept Clarifications | A-Level 生物：概念辨析

A strong performance in A-Level Biology requires more than memorising facts; you must be able to distinguish between closely related terms that often appear in exam questions. Misinterpreting ‘gene’ and ‘allele’ or confusing mitosis with meiosis can cost valuable marks. This article clarifies ten of the most commonly confused concept pairs, providing you with precise definitions and comparisons to strengthen your revision.

在A-Level生物考试中取得好成绩不仅仅靠记忆事实，更重要的是能够区分那些容易混淆的相关术语。误把“基因”和“等位基因”混为一谈，或者分不清有丝分裂和减数分裂，都可能导致丢分。本文辨析十个最常混淆的概念对，给出准确定义和对比，帮助你巩固复习。

1. Prokaryotic Cells vs Eukaryotic Cells | 原核细胞与真核细胞

Prokaryotic cells lack a membrane-bound nucleus; their DNA is circular and lies freely in the cytoplasm. They also lack membrane-bound organelles such as mitochondria and chloroplasts. Ribosomes in prokaryotes are smaller (70S) compared to those in eukaryotes (80S).

原核细胞没有膜包被的细胞核，其DNA呈环状，游离在细胞质中。它们也没有线粒体、叶绿体等膜包被的细胞器。原核生物的核糖体较小（70S），而真核生物为80S。

Additionally, prokaryotic cell walls (in bacteria) contain peptidoglycan, while eukaryotic cell walls, when present, are made of cellulose in plants or chitin in fungi. Eukaryotic cells also contain linear DNA associated with histone proteins inside a nucleus.

此外，原核细胞壁（细菌）含有肽聚糖，而真核细胞壁（如植物细胞壁由纤维素构成，真菌由几丁质构成）。真核细胞还含有位于细胞核内、与组蛋白结合的线性DNA。

2. Mitosis vs Meiosis | 有丝分裂与减数分裂

Mitosis produces two genetically identical diploid daughter cells, which is essential for growth, repair and asexual reproduction. It involves one round of division and maintains the parent cell’s chromosome number.

有丝分裂产生两个遗传相同的二倍体子细胞，这是生长、修复和无性繁殖所必需的。它只进行一次分裂，维持亲代细胞的染色体数目不变。

Meiosis, in contrast, generates four genetically non-identical haploid gametes via two consecutive divisions. During meiosis I, homologous chromosomes pair up to form bivalents, and crossing over exchanges genetic material between chromatids, while independent assortment further increases variation.

相反，减数分裂通过两次连续分裂产生四个遗传上不同的单倍体配子。在减数第一次分裂中，同源染色体配对形成二价体，交叉互换在染色单体间交换遗传物质，而自由组合进一步增加变异。

3. Gene vs Allele | 基因与等位基因

A gene is a specific sequence of DNA that codes for a polypeptide or a functional RNA molecule. Each gene occupies a particular locus on a chromosome.

基因是编码多肽或功能性RNA分子的一段特定DNA序列。每个基因占据染色体上的一个特定基因座。

An allele is one of two or more alternative versions of the same gene. Alleles arise by mutation and are found at the same locus on homologous chromosomes. For example, the gene for flower colour in pea plants can have an allele for purple and an allele for white.

等位基因是同一基因的两种或多种不同形式之一。等位基因由突变产生，位于同源染色体上的相同基因座。例如，豌豆花色基因可以有一个紫色等位基因和一个白色等位基因。

4. Genotype vs Phenotype | 基因型与表现型

Genotype refers to the full set of alleles an organism carries for a particular gene or set of genes. It is the genetic makeup inherited from the parents.

基因型指生物体针对某个或某些基因所携带的全部等位基因，即遗传自亲本的遗传组成。

Phenotype is the observable characteristic resulting from the interaction between the genotype and the environment. A classic example is that the same rabbit genotype can produce a different coat colour depending on temperature (e.g. Himalayan rabbits).

表现型是基因型与环境相互作用所产生的可观察特征。经典例子是同一种兔子基因型在不同温度下可呈现不同的毛色（如喜马拉雅兔）。

5. Active Transport vs Passive Transport | 主动运输与被动运输

Passive transport, including simple diffusion, facilitated diffusion (via channel

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