B1 - Mitosis

• Mitosis is the process by which cells divide to produce two identical daughter cells.
• Cells


  • Require a continuous supply of new cells for growth, development and repair
  • Particularly true for young organisms to grow in size
  • Also true for older organisms to replace lost cells
• Cell cycle


  The life cycle of the cell from the time it was made to the time it divides into two new cells
• Main stages of the cell cycle

  • Growth
  • DNA replication
  • Mitosis and division (cytokinesis)
• DNA in a cell

  • Usually spread out in long strings when cell is not dividing
  • Condenses into chromosomes when cell starts to prepare for division
  • Each chromosome contains a large number of genes that control development of different characteristics
• Eukaryotic cells


  Have two copies of each chromosome, one from mother and one from father
• Humans have 23 pairs of chromosomes, 46 in total
• Chromosome duplication


  1. Each chromosome duplicates, with the duplicate staying attached to the original

  2. Resulting in an X-shaped chromosome with two identical arms
• Chromosome alignment and separation

  1. Chromosomes line up along the center of the cell

  2. Fibers from either side of the cell attach to respective halves of each chromosome

  3. Fibers pull the chromosome arms to opposite sides of the cell, breaking the chromosomes in half
• Cell division (cytokinesis)


  1. Cell membrane and cytoplasm pull apart, forming two daughter cells

  2. Each daughter cell has the same DNA as the parent cell
• Daughter cells can then undergo the cell cycle again