Cell Division

• Chromosomes

  Contained in the nucleus.

  Each made from one DNA molecule.

  Found in pairs; one chromosome in the pair is inherited from the mother and the other from the father.

  23 pairs of chromosomes in each human cell; 46 total chromosomes.
• Cell Cycle

  Series of three stages in the life cycle of a cell:

  1 - Growth phase.

  2 - Mitosis.

  3 - Cytokinesis.
• Growth phase

  Number of chromosomes is doubled, resulting in two copies of each chromosome. These initially remain attached to each other; each strand is called a chromatid.

  Number of organelles increases.
• Mitosis

  Chromosomes line up at the equator of the cell and cell fibres pull each chromatid to either side of the cell.

  A new nucleus is formed around each new group of chromosomes.
• Cytokinesis

  The cell membrane and cytoplasm divide, resulting in the formation of two genetically identical daughter cells.
• Role of the cell cycle

  When an egg cell is fertilised by a sperm cell, the resulting zygote divides continuously by mitosis to form an embryo.

  Replaces damaged cells.
• Stem cells

  A stem cell is an undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation.
• Embryonic stem cells

  Form when an egg cell and sperm cell fuse to form a zygote.

  Can differentiate into any type of specialised cell in the body.

  Scientists can clone these cells and direct them to differentiate into any cell in the body.

  Used to treat type 1 diabetes by replacing faulty insulin-producing cells or nerve cells to treat individuals with paralysis.
• Adult stem cells

  Found in the bone marrow.

  Limited ability to differentiate.

  Mainly produce blood cells.
• Meristem cells

  Found on the tips of roots and shoots.

  Can differentiate into any type of plant cell, and retain this ability throughout the life of the plant.

  Can be used to make clones of the plant; helps preserve endangered plant species from extinction or mass produce plants with desired characteristics.
• Therapeutic cloning

  Involves an embryo being produced with the same genes as the patient.

  Embryo produced is then harvested to obtain its embryonic stem cells.

  These could be grown into any cells the patient needed.

  Would not be rejected by the patient's body as they possess the same genetic information as the patient.
• Benefits of stem cell research

  Can be used to replace damaged or diseased body parts.

  Unwanted embryos from fertility clinics could be used as they would otherwise be discarded.
• Problems with stem cell research

  Process of differentiation is not yet fully understood, so it is hard to control stem cells to form the cells we desire.

  Removal of stem cells results in destruction of embryo - ethical/religious objections.

  If the stem cells are contaminated, infections may be passed to individual.