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Mitosis: The Process of Cell Division

Handout
Grade 11
English

Mitosis: The Process of Cell Division

Introduction

Mitosis is a fundamental process in all living organisms, essential for growth, repair, and asexual reproduction. It is the process by which a single eukaryotic cell divides into two identical daughter cells. This ensures that each new cell receives a complete and identical set of chromosomes from the parent cell. Mitosis is a continuous process, but for descriptive purposes, it is typically divided into four main phases: prophase, metaphase, anaphase, and telophase, followed by cytokinesis.

Phases of Mitosis

Prophase

During prophase, the cell's chromatin, which is normally dispersed, condenses into visible chromosomes. Each chromosome consists of two identical sister chromatids joined at a centromere. The nuclear envelope begins to break down, and the spindle fibers (microtubules) start to form from the centrosomes, which move towards opposite poles of the cell.

Metaphase

In metaphase, the chromosomes align along the cell's equatorial plane, known as the metaphase plate. This alignment is crucial for ensuring that each daughter cell receives one copy of each chromosome. The spindle fibers attach to the centromeres of the sister chromatids, preparing them for separation.

Anaphase

Anaphase is characterized by the separation of the sister chromatids. The centromeres divide, and the now individual chromosomes are pulled apart by the shortening of the spindle fibers towards opposite poles of the cell. This movement ensures that each pole receives an identical set of chromosomes.

Telophase

During telophase, the chromosomes arrive at the poles and begin to decondense, returning to their chromatin state. New nuclear envelopes form around the two sets of chromosomes, creating two distinct nuclei within the single parent cell. The spindle fibers disappear.

Cytokinesis

Following telophase, cytokinesis occurs, which is the physical division of the cytoplasm. In animal cells, a cleavage furrow forms and pinches the cell into two. In plant cells, a cell plate forms in the middle, eventually developing into a new cell wall, separating the two daughter cells.

Significance

Mitosis is vital for several biological processes, including the growth of multicellular organisms from a single zygote, the repair of damaged tissues, the replacement of old or dead cells, and asexual reproduction in many single-celled and some multicellular organisms. It ensures genetic continuity and maintains the chromosome number from one cell generation to the next.