📚 IGCSE Biology: Mitosis Revision Notes | IGCSE 生物：有丝分裂 考点精讲
Mitosis is one of the core topics in the IGCSE Biology syllabus. It refers to the process by which a single cell divides to produce two genetically identical daughter cells. In this article, we will break down every key stage, essential vocabulary, and common exam pitfalls so you can approach mitosis questions with total confidence.
有丝分裂是 IGCSE 生物课程的核心主题之一，指的是一个细胞分裂产生两个遗传上完全相同的子细胞的过程。在这篇文章中，我们将拆解每个关键阶段、必备术语和常见考试陷阱，让你能够信心十足地应对有丝分裂题目。
1. Introduction to Mitosis | 有丝分裂简介
Mitosis is a type of nuclear division that takes place in body cells (somatic cells). It maintains the diploid chromosome number, ensuring that each daughter cell receives an exact copy of the parent cell’s DNA. The process is continuous but is described in four main stages: prophase, metaphase, anaphase, and telophase.
有丝分裂是一种发生在体细胞中的核分裂类型。它维持二倍体染色体数目，确保每个子细胞获得亲代细胞 DNA 的精确副本。这个过程是连续的，但通常被描述为四个主要阶段：前期、中期、后期和末期。
2. The Importance of Mitosis | 有丝分裂的重要性
Mitosis is essential for growth, repair, and asexual reproduction. When a zygote develops into an embryo, mitosis generates all the cells needed. It also replaces damaged or dead cells, such as skin cells and red blood cells. In many organisms, mitosis allows for cloning through asexual reproduction.
有丝分裂对于生长、修复和无性生殖至关重要。当受精卵发育成胚胎时，有丝分裂产生了所有需要的细胞。它还能替换受损或死亡的细胞，例如皮肤细胞和红细胞。在许多生物中，有丝分裂允许通过无性繁殖进行克隆。
3. Key Terminology: Chromosomes, Chromatids, Centromere | 关键术语：染色体、染色单体、着丝粒
You must be able to use these terms accurately. A chromosome is a long DNA molecule that coils around proteins. Before mitosis, each chromosome replicates, forming two identical sister chromatids joined at a region called the centromere. Once chromatids separate, each becomes an individual chromosome.
你必须能够准确使用这些术语。染色体是一条缠绕在蛋白质上的长 DNA 分子。在有丝分裂前，每条染色体复制，形成两条相同的姐妹染色单体，它们在一个叫做着丝粒的区域连接。一旦染色单体分离，每条都成为单独的染色体。
- Chromosome: a thread-like structure of DNA that carries genetic information.
- 染色体: 一种携带遗传信息的线状 DNA 结构。
- Chromatid: one of the two identical copies of a replicated chromosome.
- 染色单体: 复制染色体中两个相同副本之一。
- Centromere: the point where two chromatids are held together.
- 着丝粒: 两条染色单体连接在一起的位置。
4. The Cell Cycle Overview | 细胞周期概述
Mitosis is only one part of the cell cycle. The cycle consists of interphase (G1, S, G2 phases) and the mitotic phase (mitosis and cytokinesis). During interphase, the cell grows, carries out its normal functions, and replicates its DNA. Most of the cell cycle is spent in interphase.
有丝分裂只是细胞周期的一部分。周期包括间期（G1 期、S 期、G2 期）和有丝分裂期（有丝分裂与胞质分裂）。在间期，细胞生长、执行正常功能并复制 DNA。细胞周期的大部分时间都处于间期。
5. Interphase: Before Mitosis | 间期：有丝分裂之前
Interphase is often wrongly called the ‘resting phase’. In reality, the cell is extremely active. In the S phase, DNA replication occurs, so each chromosome now consists of two chromatids. The cell also synthesises proteins and increases the number of organelles, preparing for division.
间期常被错误地称为”休息期”。实际上，细胞极其活跃。在 S 期，DNA 复制发生，因此每条染色体现在由两条染色单体组成。细胞还合成蛋白质并增加细胞器的数量，为分裂做准备。
6. Prophase: Chromosomes Condense | 前期：染色体凝缩
Prophase is the first stage of mitosis. The chromatin fibres coil and condense to become visible chromosomes. Each chromosome appears as two sister chromatids held together by a centromere. The nuclear membrane breaks down, the nucleolus disappears, and the spindle apparatus begins to form from the centrosomes.
前期是有丝分裂的第一个阶段。染色质纤维螺旋化、凝缩，成为可见的染色体。每条染色体表现为由着丝粒连接在一起的两条姐妹染色单体。核膜解体，核仁消失，纺锤体从中心体开始形成。
In animal cells, centrioles (present in centrosomes) move to opposite poles and organise spindle fibres. Plant cells do not have centrioles but still form a spindle.
在动物细胞中，中心体里的中心粒移向两极并组织纺锤丝。植物细胞没有中心粒，但仍会形成纺锤体。
7. Metaphase: Chromosomes Align | 中期：染色体排列
During metaphase, the chromosomes line up along the equator (metaphase plate) of the cell. Spindle fibres attach to the centromeres of each chromosome. This alignment ensures that when the chromatids separate, each new cell will receive one copy of each chromosome.
在中期，染色体排列在细胞的赤道板（中期板）上。纺锤丝附着于每条染色体的着丝粒。这种排列确保了当染色单体分离时，每个新细胞会获得每条染色体的一个副本。
Chromosome alignment → controlled by spindle fibres
染色体排列 → 由纺锤丝控制
8. Anaphase: Chromatids Separate | 后期：染色单体分离
Anaphase begins when the centromeres split. The spindle fibres shorten, pulling the sister chromatids apart to opposite poles of the cell. Once separated, each chromatid is now referred to as a separate chromosome. The cell stretches as the poles move further apart.
后期从着丝粒分裂开始。纺锤丝缩短，将姐妹染色单体拉向细胞的两极。一旦分离，每条染色单体现在被称为一条单独的染色体。随着两极进一步分开，细胞被拉长。
IGCSE examiners often ask you to count the number of chromosomes at this stage. If a human cell has 46 chromosomes at the start, in anaphase there are 92 separate chromosomes briefly, until the cell divides.
IGCSE 考官常会要求计算这个阶段的染色体数量。如果一个人类细胞开始时拥有 46 条染色体，那么在后期会短暂出现 92 条独立的染色体，直到细胞分裂。
9. Telophase and Cytokinesis | 末期与胞质分裂
In telophase, the separated chromosomes reach the poles and begin to decondense back into chromatin. New nuclear membranes form around each set of chromosomes, and the nucleoli reappear. The spindle fibres disintegrate.
在末期，分离的染色体到达两极并开始解旋成染色质。新的核膜在每组染色体周围形成，核仁重新出现。纺锤丝分解消失。
Cytokinesis is the division of the cytoplasm. In animal cells, the cell membrane pinches inward to form a cleavage furrow, eventually splitting the cell into two. In plant cells, a cell plate forms at the equator, which develops into a new cell wall.
胞质分裂是指细胞质的分裂。在动物细胞中，细胞膜向内凹陷形成分裂沟，最终将细胞一分为二。在植物细胞中，赤道板位置形成细胞板，之后发育成新的细胞壁。
10. Mitosis in Plant vs. Animal Cells | 植物与动物细胞有丝分裂对比
The fundamental mechanism of mitosis is the same in plants and animals, but there are a few structural differences that are frequently tested. The table below summarises the key contrasts.
有丝分裂的基本机制在植物和动物中是相同的，但存在一些经常考查的结构差异。下表总结了关键对比。
| Feature | Animal Cells | Plant Cells |
|---|---|---|
| Centrioles | Present in centrosomes | Absent (spindle still forms) |
| Cytokinesis | Cleavage furrow pinches the cell | Cell plate forms, creating a new cell wall |
| Cell shape | Rounds up during division | Maintains shape due to rigid cell wall |
| 特征 | 动物细胞 | 植物细胞 |
|---|---|---|
| 中心粒 | 存在于中心体中 | 无（但仍形成纺锤体） |
| 胞质分裂 | 分裂沟将细胞缢缩 | 细胞板形成，产生新细胞壁 |
| 细胞形状 | 分裂时变圆 | 因刚性细胞壁而保持形状 |
11. Mitosis vs. Meiosis | 有丝分裂与减数分裂比较
Students often confuse mitosis with meiosis. Mitosis produces two genetically identical diploid daughter cells, used for growth and repair. Meiosis produces four genetically different haploid gametes, used for sexual reproduction. Knowing these distinctions is essential for IGCSE exams.
学生经常混淆有丝分裂和减数分裂。有丝分裂产生两个遗传相同的二倍体子细胞，用于生长和修复。减数分裂产生四个遗传不同的单倍体配子，用于有性繁殖。了解这些区别对 IGCSE 考试至关重要。
- Mitosis: one division → two diploid cells (2n → 2n)
- 有丝分裂: 一次分裂 → 两个二倍体细胞 (2n → 2n)
- Meiosis: two divisions → four haploid cells (2n → n)
- 减数分裂: 两次分裂 → 四个单倍体细胞 (2n → n)
- Mitosis produces genetically identical cells; meiosis introduces variation through crossing over and independent assortment.
- 有丝分裂产生遗传相同的细胞；减数分裂通过交叉互换和独立分配引入变异。
12. Common Exam Questions and Tips | 常见考题与技巧
You will almost always be asked to identify stages of mitosis from diagrams or micrographs. Look for key clues: condensed chromosomes in prophase, aligned at the equator in metaphase, pulling apart in anaphase, and two clusters at opposite ends in telophase. Make sure you can draw labelled diagrams of the stages.
你几乎总会被要求从示意图或显微照片中识别有丝分裂的阶段。寻找关键线索：前期染色体凝缩，中期排列在赤道板，后期分离并移向两极，末期在两端形成两簇。务必能够画出带标记的阶段示意图。
Be prepared to state the importance of mitosis in human biology, such as healing wounds or replacing the lining of the gut. Calculations involving chromosome numbers are common: after mitosis, daughter cells have the same number as the parent cell.
准备好阐述有丝分裂在人类生物学中的重要性，例如愈合伤口或替换肠道内壁。涉及染色体数目的计算很常见：有丝分裂后，子细胞与亲代细胞染色体数目相同。
Finally, remember that cancer is essentially uncontrolled mitosis. Understanding the cell cycle control mechanisms helps explain how tumours develop, which is another potential IGCSE question.
最后，记住癌症本质上是失控的有丝分裂。理解细胞周期的调控机制有助于解释肿瘤如何形成，这是另一个潜在的 IGCSE 考题。
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