All cells arise from other cells

• Mitosis produces two daughter cells that have the same number of chromosomes (as the parent cell and each other).
• During interphase the DNA and organelles are replicated
• Mitosis has 4 sub-phases: prophase, metaphase, anaphase and teleophase
• As mitosis begins the chromosomes are made of 2 strands which are joined in the middle by the centromere - the separate strands are called chromatids.
• During prophase the chromosomes condense and become visible, centrioles move to opposite poles of the cell and form the spindle fibres. The nuclear envelope breaks down so the chromosomes are free in the cytoplasm
• During metaphase the spindle fibres attach to the centromere of the chromosomes, and pull the chromosomes to the equator of the cell
• During anaphase the spindle fibres shorten causing the sister chromatids to opposite poles of the cell
• During teleophase, the chromosomes reach the opposite poles of the cell and become indistinct (decondense back into chromatin). The spindle fibres break down and the nuclear envelope and the nucleolus reform
• During cytokinesis the cytoplasm reforms so two daughter cells are formed
• Uncontrolled cell division leads to the formation of tumours and cancers
• Describe the two treatments to control the rate of cell division

  1. Prevent DNA from replicating
  2. Inhibit metaphase stage of cell cycle by interfering with spindle fibre formation
• The mitotic index is the ‘Number of cells in a population undergoing mitosis : Total number of cells in a population’
• Binary fission is the process by which prokaryotic cells divide
• Describe the process of Binary Fission

  1. Circular DNA molecule replicates, plasmids present in the cell are also replicated.
  2. The cell membrane grows between the two circular DNA molecules, causing the cytoplasm to divide.
  3. New cell wall forms, the result is two identical daughter cells
• Describe the process of virus replication

  1. The virus attaches to the host cell via attachement proteins.
  2. The virus injects nucleic acids into the host cell
  3. The viral nucleic acid then instructs the host cells metabolic processes to produce components of the virus (i.e. nucleic acids + proteins) which can be assembled into a new virus