Mitosis: Edexcel GCSE Biology Revision Guide | 有丝分裂考点精讲

📚 Mitosis: Edexcel GCSE Biology Revision Guide | 有丝分裂考点精讲

Mitosis is a fundamental process in GCSE Edexcel Biology. It produces two genetically identical daughter cells and is vital for growth, repair, and asexual reproduction. This guide covers the cell cycle, the stages of mitosis, chromosome behaviour, and how mitosis relates to cancer and calculating mitotic index. Mastering these concepts will help you explain how organisms grow and why tissues can heal.

有丝分裂是GCSE Edexcel生物学的核心过程。它产生两个遗传上完全相同的子细胞，对生长、修复和无性繁殖至关重要。本指南涵盖细胞周期、有丝分裂各阶段、染色体行为以及有丝分裂与癌症的关系及有丝分裂指数的计算。掌握这些概念有助于解释生物体如何生长以及组织为何能愈合。

1. What is Mitosis? | 什么是有丝分裂？

Mitosis is the division of the cell nucleus that results in two daughter nuclei, each with an identical set of chromosomes to the parent cell. It is followed by cytokinesis, which divides the cytoplasm, forming two separate cells.

有丝分裂是细胞核的分裂过程，产生两个子细胞核，每个子细胞核拥有与亲代细胞完全相同的一套染色体。有丝分裂之后发生胞质分裂，将细胞质分开，形成两个独立的细胞。

The daughter cells produced by mitosis are diploid (2n), meaning they contain the full paired set of chromosomes. In humans, that is 46 chromosomes in each new cell. Mitosis ensures genetic continuity.

有丝分裂产生的子细胞是二倍体（2n），意味着它们含有全套成对的染色体。在人类中，每个新细胞含有46条染色体。有丝分裂确保了遗传连续性。

2. The Cell Cycle: An Overview | 细胞周期总览

The cell cycle describes the life of a cell from its formation to its own division into two daughter cells. It is divided into interphase and the mitotic phase. Interphase accounts for about 90% of the cycle.

细胞周期描述了细胞从形成到自身分裂成两个子细胞的整个过程。它分为间期和有丝分裂期。间期约占整个周期的90%。

Interphase is subdivided into three stages: G₁ (first gap), S (synthesis), and G₂ (second gap). The mitotic phase includes mitosis (prophase, metaphase, anaphase, telophase) and cytokinesis.

间期细分为三个阶段：G₁期（第一间隙期）、S期（合成期）和G₂期（第二间隙期）。有丝分裂期包括有丝分裂（前期、中期、后期、末期）和胞质分裂。

Cells that are not actively dividing may exit the cycle and enter a resting state called G₀. Nerve cells and muscle cells often stay in G₀ permanently.

不活跃分裂的细胞会退出周期，进入称为G₀期的静止状态。神经细胞和肌细胞通常永久停留在G₀期。

3. Interphase: G₁, S, and G₂ | 间期：G₁、S 和 G₂期

During G₁ phase, the cell grows in size, synthesises proteins, and produces new organelles. Metabolic activity is high as the cell prepares for DNA replication.

在G₁期，细胞体积增大，合成蛋白质并产生新的细胞器。细胞代谢活动旺盛，为DNA复制做准备。

S phase is when DNA replication occurs. Each chromosome is duplicated, resulting in two identical copies called sister chromatids, held together at a region called the centromere.

S期是DNA复制发生的时期。每条染色体都被复制，产生两个相同的拷贝，称为姐妹染色单体，它们通过着丝粒连接在一起。

In G₂ phase, the cell continues to grow and synthesises proteins needed for mitosis, such as tubulin to build spindle fibres. The cell checks for DNA damage before entering mitosis.

在G₂期，细胞继续生长并合成有丝分裂所需的蛋白质，例如构建纺锤体的微管蛋白。细胞在进入有丝分裂前会检查DNA是否受损。

4. Chromosomes and Chromatids | 染色体与染色单体

Before replication, chromosomes exist as single structures. When S phase completes each chromosome consists of two sister chromatids joined at the centromere. These chromatids are genetically identical.

复制前，染色体以单条结构存在。当S期完成后，每条染色体由两条通过着丝粒相连的姐妹染色单体组成。这些染色单体在遗传上完全相同。

Human body cells normally contain 46 chromosomes (23 pairs). After DNA replication, there are still 46 chromosomes, but the DNA content has doubled because each chromosome now has two chromatids.

人体细胞通常含有46条染色体（23对）。DNA复制后，染色体数目仍为46条，但DNA含量加倍，因为每条染色体现在含两个染色单体。

During mitosis, the centromeres divide in anaphase, and the sister chromatids separate. Each chromatid is then considered an individual chromosome.

在有丝分裂后期，着丝粒分裂，姐妹染色单体随之分离。此时每条染色单体被视为一条独立的染色体。

5. Prophase – Chromosomes Condense | 前期 – 染色体凝集

Prophase is the first stage of mitosis. The chromatin fibres coil tightly, becoming shorter and thicker, and are now visible as distinct chromosomes under a light microscope.

前期是有丝分裂的第一阶段。染色质纤维高度螺旋化，变得更短、更粗，此时在光学显微镜下可见为清晰的染色体。

The nuclear envelope begins to break down, and the nucleolus disappears. In animal cells, centrioles move to opposite poles and start forming spindle fibres. Plant cells lack centrioles but still produce spindle fibres.

核膜开始解体，核仁消失。在动物细胞中，中心粒移向两极并开始形成纺锤丝。植物细胞没有中心粒，但仍会产生纺锤丝。

Each chromosome, consisting of two sister chromatids, becomes attached to spindle fibres via the centromere. The chromosomes start moving towards the centre of the cell.

每条由两个姐妹染色单体构成的染色体通过着丝粒与纺锤丝相连。染色体开始向细胞中央移动。

6. Metaphase – Chromosomes Align | 中期 – 染色体排列在赤道板

In metaphase, the chromosomes align along the equatorial plane (metaphase plate) of the cell. This arrangement ensures that each daughter cell will receive one copy of each chromosome.

在中期，染色体排列在细胞的赤道平面（中期板）上。这种排列方式确保每个子细胞将获得每条染色体的一个拷贝。

The spindle fibres from opposite poles attach to the centromeres. The alignment is controlled by opposing forces that pull the chromosomes into the middle, and this is a key checkpoint before anaphase begins.

来自两极的纺锤丝分别附着在着丝粒上。染色体的排列受对立力量的调控，将它们拉到中间位置，这是后期开始前的一个关键检查点。

7. Anaphase – Chromatids Separate | 后期 – 染色单体分离

Anaphase begins abruptly when the centromeres divide. The sister chromatids of each pair are pulled apart by the shortening of spindle fibres and move towards opposite poles of the cell.

当着丝粒分裂时，后期突然开始。每对姐妹染色单体在纺锤丝缩短的作用下分开，并移向细胞的两极。

Once separated, each chromatid is now an independent chromosome. The cell briefly contains double the diploid number of chromosomes (e.g., 92 in humans) because the chromatids have become distinct chromosomes.

一旦分离，每条染色单体就成为一条独立的染色体。此时细胞内染色体数目暂时是二倍体的两倍（例如人类细胞为92条），因为染色单体已变成了独立的染色体。

This stage consumes the most energy, provided by ATP from respiration. The separation ensures that each pole receives an identical set of genetic information.

此阶段消耗的能量最多，由细胞呼吸产生的ATP提供。染色体的分离确保每个极都获得一套完全相同的遗传信息。

8. Telophase and Cytokinesis: Two New Cells | 末期与胞质分裂：两个新细胞形成

In telophase, the separated chromosomes reach the poles and begin to decondense back into chromatin. New nuclear envelopes form around each set of chromosomes, and the nucleolus reappears.

在末期，分离的染色体到达两极，并开始解旋恢复为染色质。每组染色体周围形成新的核膜，核仁重新出现。

Cytokinesis is the division of the cytoplasm that follows telophase. In animal cells, a cleavage furrow pinches the cell membrane inward until the cell splits into two. In plant cells, vesicles gather at the equator and fuse to form a new cell plate, which develops into a new cell wall.

胞质分裂是末期之后细胞质的分裂。在动物细胞中，分裂沟使细胞膜向内缢缩，直至细胞一分为二。在植物细胞中，高尔基体小泡聚集在赤道板位置，融合形成新的细胞板，进而发育成新的细胞壁。

At the end of cytokinesis, two genetically identical daughter cells are produced, each with the same diploid number of chromosomes as the original parent cell.

胞质分裂结束时，产生两个遗传上完全相同的子细胞，每个子细胞具有与原始母细胞相同的二倍体染色体数目。

9. Importance of Mitosis | 有丝分裂的重要性

Mitosis is essential for growth in multicellular organisms. It increases the number of cells without changing the genetic information, allowing organisms to develop from a single fertilised egg to an adult.

有丝分裂对多细胞生物的生长至关重要。它增加了细胞数量而不改变遗传信息，使生物体能够从一个受精卵发育为成体。

It also allows for the repair and replacement of damaged or worn-out cells. For example, skin cells and the cells lining the gut are constantly replaced by mitotic division.

它还能修复和替换受损或衰老的细胞。例如，皮肤细胞和肠道内壁细胞通过有丝分裂不断更新。

In single-celled organisms such as yeast and amoeba, mitosis is a mechanism of asexual reproduction, producing offspring that are genetically identical to the parent.

在酵母菌和变形虫等单细胞生物中，有丝分裂是一种无性繁殖机制，产生与亲代遗传物质完全相同的后代。

10. Mitosis and Cancer | 有丝分裂与癌症

Normal cells have controlled rates of mitosis and respond to signals that regulate the cell cycle. Cancer is a result of uncontrolled cell division caused by mutations in genes that control the cycle.

正常细胞的有丝分裂速率受到严格控制，并响应细胞周期的调控信号。癌症是由于控制细胞周期的基因发生突变，导致细胞不受控制地分裂的结果。

Cancer cells do not respond to signals that would normally limit mitosis. They can divide indefinitely, forming a mass of unspecialised cells called a tumour.

癌细胞对通常会限制有丝分裂的信号无反应。它们可以无限分裂，形成一团未特化的细胞，称为肿瘤。

Malignant tumours can invade surrounding tissues and spread to other parts of the body via the blood or lymph system, a process called metastasis. Benign tumours do not spread but can still cause damage by pressing on organs.

恶性肿瘤会侵入周围组织，并通过血液或淋巴系统扩散到身体其他部位，这一过程称为转移。良性肿瘤不会扩散，但仍可能因压迫器官而带来危害。

11. Calculating Mitotic Index | 计算有丝分裂指数

The mitotic index is the proportion of cells in a tissue that are undergoing mitosis. It can be used to estimate the rate of cell division, for example in root tips or tumour samples.

有丝分裂指数是组织中正在进行有丝分裂的细胞所占的比例。可用于估算细胞分裂的速率，例如在根尖或肿瘤样本中。

Mitotic Index = Number of cells in mitosis ÷ Total number of cells × 100%

有丝分裂指数 = 处于有丝分裂的细胞数 ÷ 细胞总数 × 100%

A high mitotic index may indicate a growing tissue, such as a meristem, or a rapidly dividing tumour. In laboratory practicals, you may stain root tip cells with toluidine blue and count cells in prophase, metaphase, anaphase, and telophase under a microscope to calculate this value.

有丝分裂指数高可能表示生长中的组织（如分生组织），或是快速分裂的肿瘤。在实验操作中，可以用甲苯胺蓝对根尖细胞进行染色，并在显微镜下计数处于前期、中期、后期和末期的细胞数来计算该值。

12. Key Points Summary | 核心要点总结

The table below summarises the main events of the mitotic stages, ensuring you have a quick revision reference.

下表总结了有丝分裂各阶段的主要事件，可作快速复习参考。

Stage	Key Events (English / 中文)
Prophase	Chromosomes condense, nuclear envelope breaks down. 染色体凝集，核膜解体。
Metaphase	Chromosomes align at the equator, spindle fibres attach. 染色体排列在赤道板，纺锤丝附着。
Anaphase	Centromeres divide, chromatids pulled to poles. 着丝粒分裂，染色单体拉向两极。
Telophase	Nuclear envelopes reform, chromosomes decondense. 核膜重新形成，染色体解旋。
Cytokinesis	Cytoplasm divides; cleavage furrow (animal) or cell plate (plant). 细胞质分裂；动物细胞形成分裂沟，植物细胞形成细胞板。

Remember that mitosis produces genetically identical cells, maintains the diploid chromosome number, and is crucial for growth, repair, and asexual reproduction. Uncontrolled mitosis leads to cancer, and mitotic index is a useful tool for studying cell division rates.

记住，有丝分裂产生遗传上完全相同的细胞，维持二倍体染色体数目，对生长、修复和无性繁殖至关重要。失控的有丝分裂会导致癌症，而有丝分裂指数是研究细胞分裂速率的有用工具。

Published by TutorHao | Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）