← Biology — Std 11
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Cell Division

Ch. 7Std 11

Easy Overview

Every second, millions of cells in your body are splitting in two. This chapter is about how that happens. Think of mitosis like making a photocopy — one cell becomes two identical cells. Meiosis is more like shuffling a deck of cards — it creates variety.

Why Cells Divide

Cells divide for three reasons: growth (getting bigger), repair (fixing wounds), and reproduction (making babies). A cell can't just keep getting bigger — there's a limit to how much it can handle. Dividing is more efficient than growing forever.

The Cell Cycle

The cell cycle is like a day in the life of a cell. Interphase is when the cell grows and copies its DNA — it's the 'preparation phase'. Then comes M phase (mitosis) where it actually divides. Most of a cell's life is spent in interphase, not dividing.

Mitosis — Making Copies

Mitosis produces two identical daughter cells. Phases: Prophase (DNA condenses), Metaphase (chromosomes line up), Anaphase (they split apart), Telophase (two new nuclei form). PMAT — remember it like that. This is how you grow and heal.

Meiosis — Making Gametes

Meiosis is for making sperm and eggs. It has two rounds of division — meiosis I and II. The result? Four cells, each with half the original DNA. When sperm meets egg, the full number is restored. This is why you're a mix of both parents.

Crossing Over — Why You Look Like a Mix

During meiosis I, homologous chromosomes swap pieces. This is crossing over. It's why siblings aren't identical (unless they're identical twins). It creates new combinations of genes — and that's why evolution works.

Mitosis vs. Meiosis — The Cheat Sheet

Mitosis: 1 division, 2 identical cells, same chromosome number. Used for growth. Meiosis: 2 divisions, 4 unique cells, half the chromosome number. Used for reproduction. Mitosis is cloning. Meiosis is mixing things up.

Key Points

  • •Cell division happens for growth, repair, and reproduction.
  • •Cell cycle: Interphase (G1, S, G2) → M phase.
  • •Mitosis: PMAT — Prophase, Metaphase, Anaphase, Telophase.
  • •Mitosis produces 2 identical diploid cells.
  • •Meiosis produces 4 non-identical haploid cells.
  • •Crossing over during meiosis I increases genetic diversity.
  • •Mitosis = growth and repair; Meiosis = gamete formation.
  • •DNA replication happens during S phase of interphase.

Practice Questions

  • Differentiate between mitosis and meiosis.
  • Write the stages of mitosis and what happens in each.
  • What is crossing over? When does it occur?
  • Why is meiosis called a reduction division?
  • Explain the significance of cell division.