ICSE Class 10 Biology: Cell Division — Mitosis & Meiosis Notes 2026

Why Do Cells Divide?

• Growth: increase in number and size of cells in an organism
• Repair and regeneration: replacing worn-out or damaged cells
• Reproduction: asexual reproduction by mitosis; sexual reproduction requires meiosis

Mitosis — Stages and Events

• Interphase: DNA replication (S phase); centriole duplication; G1 and G2 growth phases
• Prophase: chromatin condenses to chromosomes; nuclear envelope breaks down; spindle forms
• Metaphase: chromosomes align at cell equator (metaphase plate) — highest visibility

Mitosis — Anaphase and Telophase

• Anaphase: centromeres split; sister chromatids pulled to opposite poles by spindle fibres
• Telophase: nuclear envelopes reform around each set of chromosomes; chromosomes decondense
• Cytokinesis: cytoplasm divides — cleavage furrow in animal cells; cell plate in plant cells

Significance of Mitosis

• Produces two genetically identical daughter cells (diploid 2n → 2n + 2n)
• Maintains chromosome number; essential for growth and asexual reproduction
• Errors in mitosis can lead to cancer (uncontrolled cell division)

Meiosis — Overview

• Two successive divisions: Meiosis I (reductive) and Meiosis II (equational)
• Result: 4 haploid (n) genetically diverse cells from one diploid (2n) cell
• Occurs in gonads (ovaries and testes) to form gametes

Key Events in Meiosis I

• Prophase I: synapsis — homologous chromosomes pair (bivalent); crossing over at chiasmata
• Crossing over shuffles genetic material → genetic variation in offspring
• Metaphase I: bivalents at equator; random orientation → independent assortment

Comparison: Mitosis vs. Meiosis

• Mitosis: 1 division, 2 daughter cells, diploid, genetically identical — growth and repair
• Meiosis: 2 divisions, 4 daughter cells, haploid, genetically varied — gamete formation
• ICSE question: state two differences with correctly drawn diagrams of both