📚 GCSE WJEC Biology: Cell Division – Exam Essentials | GCSE WJEC 生物：细胞分裂考点精讲
Cell division is one of the most fundamental processes in biology, allowing organisms to grow, repair damaged tissues, and reproduce. In the WJEC GCSE Biology specification, you need to understand the details of mitosis, meiosis, binary fission, and how these processes relate to cancer, stem cells, and practical investigations. This article breaks down every key concept into clear, bilingual explanations, ensuring you are fully prepared for your exams.
细胞分裂是生物学中最基本的过程之一，它使生物体能够生长、修复受损组织以及进行繁殖。在 WJEC GCSE 生物学大纲中，你需要理解有丝分裂、减数分裂、二分分裂的细节，以及这些过程与癌症、干细胞和实验探究的关联。本文用清晰的双语解释逐一拆解每个关键概念，确保你为考试做好充分准备。
1. Chromosomes and the Cell Cycle | 染色体与细胞周期
Chromosomes are long, coiled molecules of DNA found in the nucleus of eukaryotic cells. Each chromosome carries a large number of genes. Before a cell divides, it must duplicate its DNA so that each new cell receives a complete set. This occurs during the interphase stage of the cell cycle, when chromosomes are replicated to form two identical sister chromatids held together by a centromere.
染色体是位于真核细胞核内的长而卷曲的 DNA 分子。每条染色体携带大量基因。在细胞分裂之前，它必须复制 DNA，以确保每个新细胞都能获得完整的一套遗传信息。这一过程发生在细胞周期的间期，此时染色体复制形成两条相同的姐妹染色单体，由着丝粒连接在一起。
The cell cycle consists of interphase (G₁, S, G₂) followed by M phase (mitosis and cytokinesis). During G₁ the cell grows and carries out normal functions; in S phase DNA replication occurs; in G₂ the cell prepares for division. Mitosis itself is nuclear division, while cytokinesis divides the cytoplasm, producing two genetically identical daughter cells.
细胞周期包括间期（G₁ 期、S 期、G₂ 期）和随后的 M 期（有丝分裂和胞质分裂）。在 G₁ 期细胞生长并执行正常功能；S 期进行 DNA 复制；G₂ 期细胞为分裂做准备。有丝分裂本身是细胞核分裂，而胞质分裂则把细胞质分开，最终产生两个遗传上完全相同的子细胞。
2. The Stages of Mitosis | 有丝分裂的阶段
Mitosis is divided into four distinct phases: prophase, metaphase, anaphase, and telophase. You must be able to describe what happens to the chromosomes in each stage.
有丝分裂分为四个明显的阶段：前期、中期、后期和末期。你必须能够描述每个阶段中染色体的变化。
- Prophase: Chromosomes condense and become visible as two sister chromatids joined at the centromere. The nuclear membrane breaks down, and spindle fibres begin to form.
- 前期：染色体凝缩变短、变粗，可见为两条由着丝粒相连的姐妹染色单体。核膜解体，纺锤丝开始形成。
- Metaphase: Chromosomes line up along the equator (centre) of the cell. Spindle fibres attach to the centromeres from opposite poles.
- 中期：染色体排列在细胞的赤道板（中央）上。纺锤丝从细胞两极连接到每条染色体的着丝粒上。
- Anaphase: The centromeres split, and the spindle fibres pull the sister chromatids apart to opposite poles of the cell. Each chromatid is now a separate chromosome.
- 后期：着丝粒分裂，纺锤丝将姐妹染色单体拉向细胞的两极。此时每条染色单体成为一条独立的染色体。
- Telophase: The chromosomes uncoil and become invisible again. New nuclear membranes form around each set of chromosomes, producing two nuclei.
- 末期：染色体解螺旋，重新变得不可见。两组染色体周围形成新的核膜，产生两个细胞核。
Cytokinesis then divides the cytoplasm. In animal cells, a cleavage furrow pinches the cell in two; in plant cells, a cell plate forms to separate the two daughter cells. This results in two genetically identical diploid cells (2n).
随后胞质分裂将细胞质分开。在动物细胞中，通过细胞膜内陷形成分裂沟将细胞一分为二；在植物细胞中，则形成细胞板来分隔两个子细胞。最终产生两个遗传上相同的二倍体细胞（2n）。
3. Importance of Mitosis for Growth and Repair | 有丝分裂对于生长和修复的重要性
Mitosis is essential for the growth of multicellular organisms because it increases the total number of cells. It also replaces old, damaged, or worn-out cells. For example, skin cells are constantly being shed and renewed through mitosis, and cuts or broken bones heal when new cells are produced by mitotic division. Asexual reproduction in plants and some animals also relies on mitosis, producing offspring that are genetically identical to the parent.
有丝分裂对于多细胞生物的生长至关重要，因为它增加了细胞的总数。它还能替代老旧、受损或磨损的细胞。例如，皮肤细胞不断脱落并通过有丝分裂更新，而伤口或骨折的愈合也依赖于有丝分裂产生的新细胞。植物和一些动物的无性生殖同样依赖于有丝分裂，产生与亲本基因完全相同的后代。
In plants, mitosis occurs in regions called meristems, located at the tips of roots and shoots. These cells divide rapidly, allowing the plant to grow throughout its life. Animals have stem cells in certain tissues that can divide by mitosis to replace specialized cells.
在植物中，有丝分裂发生在称为分生组织的区域，位于根尖和茎尖。这些细胞分裂迅速，使植物能够终生生长。动物在某些组织中有干细胞，可以通过有丝分裂来补充特化的细胞。
4. Meiosis and Gamete Formation | 减数分裂与配子形成
Meiosis is a type of cell division that produces gametes (sperm and egg cells in animals, pollen and ovules in plants). Unlike mitosis, meiosis involves two successive divisions – Meiosis I and Meiosis II – and results in four genetically different haploid cells (n), each with half the number of chromosomes.
减数分裂是一种产生配子的细胞分裂（动物的精子和卵细胞，植物的花粉和胚珠）。与有丝分裂不同，减数分裂包含两次连续的分裂——减数第一次分裂和减数第二次分裂——最终产生四个遗传上不同的单倍体细胞（n），每个细胞染色体数目减半。
During Meiosis I, homologous chromosomes pair up and may exchange genetic material in a process called crossing over. Then the pairs are separated, reducing the chromosome number from diploid (2n) to haploid (n). Meiosis II resembles mitosis, where the sister chromatids of each chromosome are separated. The end result is four haploid cells that are not genetically identical.
在减数第一次分裂期间，同源染色体配对并可能通过一个称为交叉的过程交换遗传物质。然后配对染色体分离，将染色体数目从二倍体（2n）减至单倍体（n）。减数第二次分裂类似于有丝分裂，每条染色体的姐妹染色单体分开。最终结果是四个单倍体细胞，它们在遗传上并不相同。
5. Genetic Variation through Meiosis | 减数分裂导致的遗传变异
Meiosis introduces genetic variation in two key ways: independent assortment and crossing over. During independent assortment, the way each pair of homologous chromosomes lines up at the equator is random, leading to different combinations of maternal and paternal chromosomes in the gametes. Crossing over, which occurs in prophase I, swaps sections of DNA between homologous chromosomes, creating new allele combinations on each chromosome.
减数分裂以两种关键方式引入遗传变异：独立分配和交叉。在独立分配过程中，每对同源染色体在赤道板上的排列方式是随机的，导致配子中母本和父本染色体的组合各不相同。交叉发生在前期 I，同源染色体之间交换 DNA 片段，在每条染色体上产生新的等位基因组合。
These mechanisms mean that each gamete contains a unique set of genetic information. When gametes fuse during fertilisation, the resulting zygote has a combination of alleles that has never existed before. This is why sexual reproduction produces offspring that are genetically different from both parents and from each other.
这些机制意味着每个配子都含有一套独特的遗传信息。当配子在受精过程中融合时，所产生的受精卵拥有前所未有的等位基因组合。这就是有性生殖产生的后代与双亲以及彼此之间遗传上各不相同的原因。
6. Comparing Mitosis and Meiosis | 有丝分裂与减数分裂的比较
Being able to compare mitosis and meiosis is a common exam requirement. Use the table below to recall the key differences.
能够比较有丝分裂和减数分裂是常见的考试要求。使用下面的表格来记住关键区别。
| Feature | Mitosis | Meiosis |
|---|---|---|
| Number of divisions | One | Two |
| Daughter cells produced | Two diploid (2n) | Four haploid (n) |
| Genetic variation | None – cells are clones | High – due to crossing over and independent assortment |
| Purpose | Growth, repair, asexual reproduction | Production of gametes for sexual reproduction |
| Occurs in | Body (somatic) cells | Reproductive organs (ovaries, testes, anthers, ovules) |
Remember, in mitosis homologous chromosomes do not pair up, and there is no crossing over. The daughter cells contain exactly the same DNA as the parent cell. In meiosis, the reduction division halves the chromosome number and shuffles the genetic information, making it essential for maintaining the chromosome number across generations after fertilisation.
记住，在有丝分裂中同源染色体不配对，也没有交叉。子细胞含有与母细胞完全相同的 DNA。在减数分裂中，减数分裂将染色体数目减半并重新组合遗传信息，这对于通过受精后维持世代间染色体数目的恒定至关重要。
7. Binary Fission in Bacteria | 细菌的二分分裂
Prokaryotic cells, such as bacteria, divide by a simpler process called binary fission. The single, circular chromosome is replicated, and the two copies move to opposite ends of the cell. The cell then elongates and splits into two genetically identical daughter cells. There is no nucleus and no spindle formation.
原核细胞，例如细菌，通过一种更简单的过程——二分分裂——进行繁殖。细菌的单一环状染色体被复制，两个拷贝移动到细胞的两端。然后细胞伸长并分裂成两个遗传上完全相同的子细胞。该过程不涉及细胞核和纺锤体的形成。
Binary fission can occur very rapidly under optimal conditions, which is why bacterial populations can grow exponentially. In WJEC exams, you might be asked to compare binary fission with mitosis – the main point is that binary fission is simpler and does not involve the stages of mitosis.
在适宜条件下，二分分裂可以非常迅速地进行，这就是细菌种群能够呈指数增长的原因。在 WJEC 考试中，你可能会被要求比较二分分裂和有丝分裂——要点在于二分分裂更简单，不涉及有丝分裂的各个阶段。
8. Cancer and Uncontrolled Cell Division | 癌症与失控的细胞分裂
Cancer arises when mutations in DNA cause the cell cycle to lose its normal controls. Cells begin to divide uncontrollably, forming a mass of abnormal cells called a tumour. Not all tumours are cancerous; benign tumours grow slowly and do not spread, while malignant tumours invade nearby tissues and may spread to other parts of the body via the blood (metastasis).
当 DNA 发生突变导致细胞周期丧失正常控制时，就会引发癌症。细胞开始不受控制地分裂，形成一团异常细胞，称为肿瘤。并非所有肿瘤都是癌性的；良性肿瘤生长缓慢且不扩散，而恶性肿瘤会侵入附近组织，并可能通过血液扩散到身体其他部位（转移）。
Risk factors for cancer include exposure to carcinogens such as UV radiation, tobacco smoke, certain viruses, and inherited genetic mutations. Understanding mitosis helps researchers develop treatments, such as chemotherapy, which target rapidly dividing cells.
癌症的危险因素包括接触致癌物质，如紫外线辐射、烟草烟雾、某些病毒以及遗传性基因突变。了解有丝分裂有助于研究人员开发治疗方法，例如化疗，它靶向快速分裂的细胞。
9. Stem Cells and Differentiation | 干细胞与分化
Stem cells are unspecialised cells that have the ability to divide by mitosis and then differentiate into various types of specialised cells. In early embryos, embryonic stem cells are totipotent (able to form any cell type), while adult stem cells found in tissues like bone marrow are multipotent (able to form several, but not all, cell types). Plants also have meristem stem cells that allow continued growth.
干细胞是未特化的细胞，它们能够通过有丝分裂进行增殖，然后分化成各种类型的特化细胞。在早期胚胎中，胚胎干细胞是全能的（能形成任何细胞类型），而在骨髓等组织中的成体干细胞是多能的（能形成多种但不是所有细胞类型）。植物也具有分生组织干细胞，支持其持续生长。
Stem cells have huge medical potential, such as treating leukaemia with bone marrow transplants or replacing damaged nerve tissue. However, the use of embryonic stem cells raises ethical issues because obtaining them usually involves destruction of an embryo. The WJEC specification expects you to discuss these benefits and ethical considerations.
干细胞具有巨大的医学潜力，例如通过骨髓移植治疗白血病或替换受损的神经组织。然而，使用胚胎干细胞会引发伦理问题，因为获取它们通常涉及破坏胚胎。WJEC 大纲要求你能够讨论这些益处和伦理考量。
10. Required Practical: Mitosis in Onion Root Tips | 必做实验：洋葱根尖有丝分裂观察
In this practical, you use a microscope to observe cells undergoing mitosis in the meristem of an onion root tip. The steps are as follows: first, place a root tip in a warm hydrochloric acid solution to soften the tissue. Then rinse, and stain with a dye such as toluidine blue to make chromosomes visible. Squash the sample gently on a slide to create a single layer of cells.
在该实验中，你需要使用显微镜观察洋葱根尖分生组织中进行有丝分裂的细胞。步骤如下：首先，将根尖放入温盐酸溶液中软化组织。然后冲洗，并用甲苯胺蓝等染料染色，使染色体可见。在载玻片上轻轻压扁样品，使其成为单层细胞。
Using the microscope, look for cells with clearly visible chromosomes. Cells in interphase will show a uniform nucleus, while cells in mitosis will display condensed chromosomes. You should be able to identify prophase, metaphase, anaphase, and telophase stages, and perhaps calculate the mitotic index (percentage of cells undergoing mitosis).
使用显微镜时，寻找有清晰可见染色体的细胞。间期的细胞会显示均匀的细胞核，而处于有丝分裂的细胞将展示凝缩的染色体。你应该能够识别前期、中期、后期和末期，并或许能够计算有丝分裂指数（正在进行有丝分裂的细胞百分比）。
It is crucial to recognise that only the meristem region (just behind the root cap) will contain dividing cells. Take care when focusing the microscope, and always draw observations using a sharp pencil, labelling the structures clearly for the exam.
关键是要认识到只有分生组织区域（刚好位于根冠之后）才含有正在分裂的细胞。使用显微镜调焦时要小心，并且一定要用削尖的铅笔绘制观察结果，在考试时清楚地标注各个结构。
Published by TutorHao | Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导