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

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

Mitosis is a fundamental process in which a eukaryotic cell divides to produce two daughter cells, each with an identical set of chromosomes to the parent. For your WJEC GCSE Biology exam, you need to understand the stages of mitosis, the behaviour of chromosomes, and the significance of this type of cell division in growth, repair, and asexual reproduction.

有丝分裂是真核细胞分裂产生两个子细胞的基本过程，每个子细胞拥有与母细胞完全相同的染色体组合。对于WJEC GCSE生物考试，你需要理解有丝分裂的各阶段、染色体的行为，以及这种细胞分裂方式在生长、修复和无性繁殖中的意义。

1. What is Mitosis? | 什么是有丝分裂？

Mitosis is a type of nuclear division that ensures each daughter cell receives an exact copy of the genetic material. It is preceded by the replication of DNA during interphase, so each chromosome consists of two identical sister chromatids joined at a region called the centromere. Mitosis separates these chromatids, distributing one copy of each chromosome into each new nucleus.

有丝分裂是一种核分裂方式，确保每个子细胞获得一份精确的遗传物质拷贝。在此之前，DNA在间期完成了复制，因此每条染色体由两条完全相同的姐妹染色单体组成，它们在称为着丝粒的区域相连。有丝分裂将这些染色单体分开，把每条染色体的一个拷贝分配到每个新细胞核中。

2. The Cell Cycle Overview | 细胞周期概述

The cell cycle describes the series of events that cells go through as they grow and divide. It consists of interphase (G₁, S, G₂ phases) and the mitotic phase (M phase), which includes mitosis and cytokinesis. In WJEC, you are expected to know that DNA replication occurs during the S phase of interphase, and that after mitosis, the cell splits into two during cytokinesis.

细胞周期描述了细胞生长和分裂所经历的一系列事件。它包括间期（G₁期、S期、G₂期）和分裂期（M期），其中M期包含有丝分裂和胞质分裂。在WJEC考试中，你需要知道DNA复制发生在间期的S期，并且在有丝分裂之后，细胞在胞质分裂中一分为二。

Mitosis itself is a continuous process but is described in four main stages: prophase, metaphase, anaphase, and telophase. Understanding what happens to the chromosomes in each stage is crucial.

有丝分裂本身是一个连续的过程，但通常被描述为四个主要阶段：前期、中期、后期和末期。理解每个阶段染色体的变化非常关键。

3. Interphase: The Preparation Stage | 间期：准备阶段

Although not officially part of mitosis, interphase is when the cell prepares for division. The cell grows, carries out normal metabolic activities, and replicates its DNA. By the end of interphase, each chromosome exists as two sister chromatids held together by a centromere. The chromosomes are not yet visible under a light microscope because they are in the form of long, thin chromatin fibres.

尽管间期并不正式属于有丝分裂，但它是细胞为分裂做准备的阶段。细胞生长、进行正常代谢活动并复制其DNA。在间期结束时，每条染色体都以两条姐妹染色单体的形式存在，由着丝粒连接。此时染色体在光学显微镜下尚不可见，因为它们是以长而细的染色质纤维形式存在。

Interphase also includes the G₁ phase (cell growth), S phase (DNA synthesis), and G₂ phase (preparation for mitosis). The key point for WJEC is that DNA replication produces two identical copies of each chromosome, doubling the amount of DNA but not the chromosome number. The chromosome number (e.g., 46 in humans) remains the same; we say the cell is still diploid (2n) but has 4c DNA content.

间期还包括G₁期（细胞生长）、S期（DNA合成）和G₂期（有丝分裂前的准备）。WJEC的关键点是：DNA复制产生了每条染色体的两个相同拷贝，使DNA含量加倍，但染色体数目不变。例如人类的染色体数目仍然是46条，我们称细胞仍然是二倍体（2n），但DNA含量为4c。

4. Prophase: Getting Organised | 前期：染色体凝集

During prophase, the chromatin fibres coil and condense to form visible chromosomes. Each chromosome appears as two sister chromatids joined at the centromere. The nuclear envelope begins to break down, and the nucleolus disappears. In the cytoplasm, the spindle fibres start to form from the centrosomes, which move to opposite poles of the cell.

在前期，染色质纤维螺旋化和凝集，形成可见的染色体。每条染色体看起来像两条由着丝粒连接的姐妹染色单体。核膜开始解体，核仁消失。在细胞质中，纺锤体纤维开始从中心体形成，中心体移向细胞两极。

In animal cells, centrioles help organise the spindle, but plant cells lack centrioles and still form a functional spindle. This is a common WJEC distinction. Drawings of prophase should show condensed chromosomes (X-shaped if drawn clearly) and the developing spindle.

在动物细胞中，中心粒协助组织纺锤体，但植物细胞没有中心粒，仍然能形成有功能的纺锤体。这是WJEC常见的区分点。前期示意图应显示凝集的染色体（如果画得清晰则呈X形）和正在形成的纺锤体。

5. Metaphase: Lining Up | 中期：染色体排列

In metaphase, the chromosomes are moved by the spindle fibres to align along the equator (metaphase plate) of the cell. The centromeres of the chromosomes are attached to spindle fibres from opposite poles. This alignment ensures that when the chromatids separate, each new cell will receive one copy of each chromosome.

在中期，染色体被纺锤体纤维移动到细胞赤道板（中期板）上排列成一行。染色体的着丝粒与来自两极的纺锤体纤维

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