📚 Mitosis in A-Level AQA Biology | A-Level AQA 生物：有丝分裂 考点精讲
Mitosis is a fundamental process in all living organisms, ensuring that two genetically identical daughter cells are produced from a single parent cell. For A-Level AQA Biology, understanding the stages of mitosis, the behaviour of chromosomes, and the role of the cell cycle is essential for both exam success and a deeper appreciation of growth, repair, and asexual reproduction. This revision guide covers every key concept, from interphase to cytokinesis, and explains the critical differences between mitosis in animal and plant cells.
有丝分裂是所有生物体中的基本过程，它确保从一个亲代细胞产生两个遗传上完全相同的子细胞。在 A-Level AQA 生物学中，理解有丝分裂的各个阶段、染色体的行为以及细胞周期的作用，对于考试成功以及深入理解生长、修复和无性繁殖至关重要。本篇复习指南涵盖了从间期到胞质分裂的每一个关键概念，并解释了动物细胞与植物细胞有丝分裂的关键差异。
1. The Cell Cycle – A Quick Overview | 细胞周期快速概览
The cell cycle is the series of events that take place in a cell leading to its division and duplication. It consists of interphase (G1, S, G2 phases) and the mitotic phase (mitosis and cytokinesis). Mitosis itself is only a small part of the overall cycle but is the phase where the nucleus divides. A-Level exams frequently ask you to identify or describe the stages in the correct order.
细胞周期是细胞中导致其分裂和复制的一系列事件。它包括间期（G1 期、S 期、G2 期）和有丝分裂期（有丝分裂和胞质分裂）。有丝分裂本身只是整个周期的一小部分，但却是细胞核分裂的阶段。A-Level 考试经常要求你按正确顺序识别或描述这些阶段。
- G1 phase: cell grows and carries out normal metabolic functions; organelles duplicate.
- G1 期：细胞生长并执行正常代谢功能；细胞器复制。
- S phase: DNA replication occurs – each chromosome now consists of two identical sister chromatids joined at a centromere.
- S 期：DNA 复制发生——此时每条染色体由两条完全相同的姐妹染色单体组成，它们在着丝粒处相连。
- G2 phase: further growth and preparation for mitosis; synthesis of spindle proteins takes place.
- G2 期：进一步生长并为有丝分裂做准备；纺锤体蛋白的合成发生。
2. Interphase – The Preparation Stage | 间期——准备阶段
Although interphase is not part of mitosis, questions on mitosis will often test your understanding of what happens before division begins. During interphase, chromosomes are not visible as distinct structures – they exist as long, thin chromatin threads. This is because the DNA is uncoiled to allow transcription and replication. The centrioles (in animal cells) replicate, and the cell builds up energy stores.
虽然间期不是有丝分裂的一部分，但关于有丝分裂的题目通常会考察你对分裂开始前所发生事件的理解。在间期，染色体并不是清晰可见的结构——它们以长而细的染色质丝的形式存在。这是因为 DNA 处于解螺旋状态，以便进行转录和复制。在动物细胞中，中心粒进行复制，细胞也积累了能量储备。
At the end of interphase, each chromosome is duplicated but still appears as a single mass; the two chromatids are held together by cohesin proteins along their length and by the centromere. It is vital to remember that a chromosome with two chromatids is still counted as a single chromosome until the centromere splits in anaphase.
间期结束时，每条染色体已经复制，但仍然以单个团块的形式出现；两条染色单体通过黏连蛋白沿其长度以及在着丝粒处被保持在一起。务必记住：一条带有两条染色单体的染色体仍然被算作一条染色体，直到着丝粒在后期分裂为止。
3. Prophase – Chromosomes Condense | 前期——染色体浓缩
Prophase is the first stage of mitosis. The chromatin fibres coil and condense, becoming visible as distinct chromosomes. Each chromosome appears as two sister chromatids joined at the centromere. The nucleolus disappears, and the nuclear envelope begins to break down into small vesicles. In animal cells, the two centrioles migrate to opposite poles of the cell, and spindle fibres start to form from tubulin proteins, creating the mitotic spindle.
前期是有丝分裂的第一个阶段。染色质纤维螺旋化并浓缩，变得清晰可见，成为分明的染色体。每条染色体表现为两条姐妹染色单体在着丝粒处相连。核仁消失，核膜开始瓦解成小囊泡。在动物细胞中，两个中心粒移向细胞两极，纺锤丝从微管蛋白开始形成，构建有丝分裂纺锤体。
A common exam question asks you to describe the difference between chromatin and chromosomes. Chromatin is the uncondensed DNA-protein complex present during interphase; chromosomes are the condensed, visible structures seen during prophase, metaphase and anaphase.
常见的考题会要求你描述染色质和染色体之间的区别。染色质是间期存在的、未凝缩的 DNA-蛋白质复合体；染色体则是在前期、中期和后期可见的、凝缩的结构。
4. Metaphase – Alignment at the Equator | 中期——赤道板排列
During metaphase, the nuclear envelope has completely broken down. Each chromosome attaches to the spindle fibres via its centromere. The kinetochore, a protein structure on the centromere, acts as the attachment site. The spindle fibres pull the chromosomes into alignment along the metaphase plate (the equator of the cell). The chromosomes are arranged so that the sister chromatids face opposite poles. This alignment ensures that when the chromatids separate, each new daughter cell receives one copy of each chromosome.
在中期，核膜已完全解体。每条染色体通过其着丝粒附着到纺锤丝上。着丝粒上的动粒（一种蛋白质结构）充当附着点。纺锤丝将染色体拉向赤道板（细胞的赤道面）并排列成行。染色体的排列方式使得姐妹染色单体朝向相反的两极。这种排列确保了当染色单体分离时，每个新的子细胞都能获得每条染色体的一个拷贝。
In AQA exams, you may be given a microscope image and asked to identify which phase is shown. Metaphase is characterised by chromosomes lined up in the middle of the cell, often appearing in a straight line when viewed from the side.
在 AQA 考试中，你可能会得到一张显微镜图像，并被要求识别其中所示的是哪个阶段。中期的特征在于染色体排列在细胞中央，从侧面观察时常呈现为一条直线。
5. Anaphase – The Separation | 后期——分离
Anaphase begins when the centromeres split. The enzyme separase cleaves the cohesin proteins holding the sister chromatids together. The spindle fibres shorten, pulling the now-separate sister chromatids (now called chromosomes) to opposite poles of the cell. The spindle fibres not attached to kinetochores elongate the cell. Anaphase results in an equal and identical set of chromosomes being moved to each end of the cell.
后期开始于着丝粒分裂。分离酶水解了将姐妹染色单体结合在一起的黏连蛋白。纺锤丝缩短，将现已分开的姐妹染色单体（此时称为染色体）拉向细胞的两极。未附着到动粒的纺锤丝则会延长细胞。后期使得一个平等且完全相同的染色体组合被移向细胞的两端。
If a question asks “at what stage do chromatids become chromosomes?”, the answer is anaphase, after the centromere divides. This is a common trick. Remember also that energy for the movement of chromosomes comes from the hydrolysis of ATP by motor proteins on the kinetochore.
如果题目问“在哪个阶段染色单体变为染色体？”，答案是后期，在着丝粒分裂之后。这是一个常见的陷阱。还要记住，染色体移动的能量来源于动粒上马达蛋白水解 ATP 的过程。
6. Telophase – Two Nuclei Form | 末期——两个细胞核形成
During telophase, the separated chromosomes reach the poles and begin to decondense back into chromatin. The spindle fibres disintegrate, and a new nuclear envelope reforms around each set of chromosomes, using fragments of the old nuclear envelope and membrane from the endoplasmic reticulum. The nucleoli also reappear. Telophase is essentially the reverse of prophase. Mitosis – the division of the nucleus – is now complete.
在末期，已分开的染色体到达两极，并开始解螺旋恢复为染色质。纺锤丝解体，一组新的核膜围绕着每一套染色体重新形成，其原料来自旧核膜的碎片和内质网膜。核仁也重新出现。末期基本上是前期的逆向过程。此时，有丝分裂——细胞核的分裂——宣告完成。
In plant cells, telophase is similar, but because plant cells lack centrioles, the spindle forms from microtubule-organising centres in the cytoplasm. A cell plate begins to form instead of a cleavage furrow (see cytokinesis).
在植物细胞中，末期与之相似，但由于植物细胞缺少中心粒，纺锤体由细胞质中的微管组织中心形成。此时，细胞板开始形成，而非形成卵裂沟（见胞质分裂）。
7. Cytokinesis – Division of the Cytoplasm | 胞质分裂——细胞质的分裂
Cytokinesis is often considered part of the M phase but is separate from mitosis. In animal cells, a cleavage furrow forms as a ring of actin and myosin microfilaments contracts around the equator of the cell, pinching it into two daughter cells. In plant cells, vesicles derived from the Golgi apparatus assemble at the equator, fusing to form a cell plate. The cell plate grows outward until it fuses with the existing cell wall, forming two separate cells. Note that plant cytokinesis differs because a rigid cell wall must be constructed.
胞质分裂通常被认为是 M 期的一部分，但与有丝分裂是分开的。在动物细胞中，由肌动蛋白和肌球蛋白微丝组成的环在细胞赤道处收缩，形成一个卵裂沟，将细胞夹断成两个子细胞。在植物细胞中，来自高尔基体的囊泡在赤道处聚集，融合成细胞板。细胞板向外生长，直到与已有的细胞壁融合，形成两个独立的细胞。请注意，植物胞质分裂的不同之处在于，必须构建一层刚性的细胞壁。
Exam marker reports note that candidates often confuse cleavage furrow (animals) and cell plate (plants). Be absolutely clear on this distinction.
考官的评卷报告指出，考生经常混淆卵裂沟（动物）和细胞板（植物）。请务必清楚地区分这两者。
8. Recognising Mitotic Stages Under the Microscope | 显微镜下识别有丝分裂阶段
In a root tip squash or other mitotic tissue preparation, you need to be able to identify the stages. Use the following visual clues:
| Stage | Visual Features |
|---|---|
| Prophase | Chromosomes visible as condensed threads; nuclear membrane may be partially present; no clear alignment. |
| Metaphase | Chromosomes aligned in a straight line across the centre (equator); spindle fibres sometimes visible. |
| Anaphase | Two groups of chromosomes moving towards opposite poles; V-shaped chromatids pulled by spindle fibres. |
| Telophase | Two clusters of decondensing chromosomes; cell plate or cleavage furrow often present; nuclear envelopes reforming. |
在一份根尖压片或其他有丝分裂组织制片中，你需要能够识别各个阶段。使用以下视觉线索：
| 阶段 | 视觉特征 |
|---|---|
| 前期 | 染色体呈浓缩的丝状可见；核膜可能部分存在；无明显排列。 |
| 中期 | 染色体在细胞中央（赤道面）排列成一条直线；纺锤丝有时可见。 |
| 后期 | 两组染色体朝相反的两极移动；被纺锤丝拉动的染色单体呈V形。 |
| 末期 | 两团正在解螺旋的染色体；常可见到细胞板或卵裂沟；核膜正在重新形成。 |
9. Mitotic Index and Cancer | 有丝分裂指数与癌症
The mitotic index is the proportion of cells in a tissue sample that are undergoing mitosis at a given time. It is calculated as:
Mitotic index = Number of cells with visible chromosomes / Total number of cells observed
. A high mitotic index indicates rapid cell division, which is a hallmark of cancerous tissues. In an exam, you might be asked to calculate the index from a table of cell counts and to comment on whether the tissue is likely cancerous.
有丝分裂指数是组织样本中某一时刻正在进行有丝分裂的细胞所占的比例。它的计算公式为：
有丝分裂指数 = 可见染色体的细胞数 / 观察到的细胞总数
。有丝分裂指数高表明细胞分裂迅速，这是癌组织的标志。在考试中，你可能会被要求从细胞计数表中计算该指数，并评论该组织是否可能癌变。
Cancer often involves mutations in genes that regulate the cell cycle, such as proto-oncogenes and tumour suppressor genes. Uncontrolled mitosis leads to a mass of genetically identical cells (a tumour). This directly links mitosis to cancer biology, a synoptic topic in AQA A-Level.
癌症通常涉及调控细胞周期的基因发生突变，例如原癌基因和抑癌基因。不受控制的有丝分裂会导致形成大量遗传上完全相同的细胞（肿瘤）。这就直接把有丝分裂与癌症生物学联系了起来，这是 AQA A-Level 中的一个综合性考点。
10. Significance of Mitosis | 有丝分裂的重要性
Mitosis is vital for the growth of multicellular organisms, for repair of damaged tissues, and for asexual reproduction in many organisms (e.g. budding in yeast, vegetative propagation in plants). Because mitosis produces daughter cells that are genetically identical to the parent cell, it maintains the chromosome number and genetic stability. This contrasts with meiosis, which produces genetically varied haploid gametes.
有丝分裂对于多细胞生物的生长、受损组织的修复以及许多生物的无性繁殖（例如酵母的出芽生殖、植物的营养繁殖）都至关重要。由于有丝分裂产生的是与亲代细胞遗传上完全相同的子细胞，它维持了染色体数目和遗传稳定性。这与减数分裂形成对比，后者产生遗传上多样化的单倍体配子。
In plants, mitosis occurs in meristems (apical and lateral), responsible for primary and secondary growth. In animals, mitosis occurs in many tissues, particularly in stem cell niches. Be prepared to give named examples of where mitosis occurs.
在植物中，有丝分裂发生于分生组织（顶端分生组织和侧生分生组织），负责初生生长和次生生长。在动物中，有丝分裂发生于多种组织中，尤其是干细胞龛中。请准备好举出有丝分裂发生部位的具体例子。
11. Key Terminology and Common Pitfalls | 关键术语与常见误区
AQA mark schemes are strict on precise terminology. Use the following terms correctly:
AQA 评分标准对术语的精确性要求很严格。请正确使用以下术语：
- Chromosome: a DNA molecule with its associated proteins; can consist of one chromatid (unreplicated) or two sister chromatids (replicated).
- 染色体：DNA 分子及其关联蛋白质；可以由一条染色单体（未复制）或两条姐妹染色单体（已复制）组成。
- Chromatid: one copy of a duplicated chromosome. Two chromatids are “sister chromatids” when joined at the centromere.
- 染色单体：复制后染色体的一份拷贝。当两条染色单体在着丝粒处相连时，它们互为“姐妹染色单体”。
- Centromere: the constricted region linking sister chromatids; serves as the attachment site for spindle fibres.
- 着丝粒：连接姐妹染色单体的缢缩区域；充当纺锤丝的附着点。
- Spindle fibres: made of tubulin microtubules; they are part of the cytoskeleton and guide chromosome movement.
- 纺锤丝：由微管蛋白微管构成；属于细胞骨架的一部分，引导染色体的移动。
- Homologous chromosomes: NOT involved in mitosis – only in meiosis. Do not confuse them.
- 同源染色体：在有丝分裂中不涉及——仅出现在减数分裂。切勿混淆。
Many students lose marks by saying “chromosomes line up in pairs” in mitosis – this is incorrect; homologous pairing only happens in meiosis I. In mitosis, individual chromosomes line up independently.
许多学生因为在有丝分裂中说“染色体成对排列”而丢分——这是不正确的；同源配对仅发生在减数第一次分裂中。在有丝分裂中，单独的染色体独立排列。
12. Exam Technique and Common Questions | 应试技巧与常见问题
AQA A-Level Biology typically asks you to:
AQA A-Level 生物学通常会要求你：
- Describe the behaviour of chromosomes during mitosis.
- 描述有丝分裂过程中染色体的行为。
- Label or identify stages from micrographs.
- 从显微照片中标记或识别阶段。
- Explain why the chromosome number remains constant.
- 解释为何染色体数目保持不变。
- Contrast mitosis in plants and animals (centrioles, cell plate vs cleavage furrow).
- 对比植物和动物细胞的有丝分裂（中心粒、细胞板 vs 卵裂沟）。
- Calculate mitotic index and interpret its significance in health and disease.
- 计算有丝分裂指数并解释其在健康与疾病中的意义。
When answering, always link structure to function. For example: “The spindle fibres shorten because of the removal of tubulin subunits; this pulls the chromatids apart using energy from ATP hydrolysis.” Use precise scientific language and avoid vague phrases like “the chromosomes move to the sides.”
作答时，总要把结构与功能联系起来。例如：“纺锤丝缩短是由于微管蛋白亚基的移除；这一过程利用 ATP 水解释放的能量将染色单体拉开。”使用精确的科学语言，避免含糊其辞，如“染色体移向两边”。
Published by TutorHao | AQA 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Cancel reply