Biology Chapter 10: Cell Cycle and Cell Division

Key Concepts

• All organisms start life from a single cell.
• Cell growth and reproduction occur through cell division.
• Cell Cycle: Sequence of events where a cell duplicates its genome, synthesizes other cellular components, and divides into two daughter cells.
• Two main phases:
  • Interphase: Preparation phase, includes G1, S, and G2 phases.
  • M Phase (Mitosis Phase): Actual cell division.

10.1 Cell Cycle

• Phases of Cell Cycle:
  • Interphase:
    • G1 Phase (Gap 1): Cell grows, performs normal functions but does not replicate DNA.
    • S Phase (Synthesis): DNA replication occurs; amount of DNA doubles.
    • G2 Phase (Gap 2): Cell continues to grow and prepares for mitosis.
  • M Phase: Includes karyokinesis (nuclear division) and cytokinesis (cytoplasmic division).

10.2 M Phase (Mitosis)

• Stages of Karyokinesis:
  • Prophase: Chromosomes condense, spindle fibers form, nuclear envelope disintegrates.
  • Metaphase: Chromosomes align at the cell equator.
  • Anaphase: Sister chromatids separate and move to opposite poles.
  • Telophase: Chromosomes decondense, nuclear envelope reforms.
• Cytokinesis:
  • Animal cells: Division via plasma membrane furrowing.
  • Plant cells: Formation of cell plate leading to new cell wall.

10.3 Significance of Mitosis

• Mitosis maintains chromosome number across cell generations.
• Essential for growth, repairing tissues, and asexual reproduction.

10.4 Meiosis

• Purpose: Formation of gametes with half the chromosome number (haploid).
• Meiosis Phases:
  • Meiosis I:
    • Prophase I: Homologous chromosomes pair (synapsis) and exchange genetic material (crossing over).
    • Metaphase I: Homologous pairs align at the equatorial plate.
    • Anaphase I: Homologous chromosomes separate.
    • Telophase I: Cells form dyads, nuclear membrane reforms.
  • Meiosis II:
    • Similar to mitosis, separates sister chromatids, results in four haploid cells.

10.5 Significance of Meiosis

• Maintains species chromosome number across generations.
• Increases genetic diversity essential for evolution.

Summary

• Cell division is a continuous and essential process for growth, repair, and reproduction.
• Mitosis: Equational division maintaining chromosome number.
• Meiosis: Reduction division halving chromosome number.
• Exercises: Questions on cell cycle phases, events, and significance.

• Exercises Section: Includes questions for further practice and understanding of the concepts.

Important Terms

• Bivalent: Pair of synapsed homologous chromosomes.
• Synapsis: Pairing of homologous chromosomes.
• Chiasmata: X-shaped regions where crossing over occurs.
• Kinetochore: Protein structure on chromatids where spindle fibers attach.

This chapter provides a thorough understanding of the cell cycle, including the phases and significance of mitosis and meiosis, essential for cell growth, reproduction, and genetic variability.