Cell division

• In the human body, cells the chromosomes are normally found in pairs
• Humans have around 24,000 genes and there are up to 2,000 genes in one human chromosome
• In the nucleus, there are structures called chromosomes
• The chromosomes are made up of coiled strands of DNA molecules
• A section of DNA that codes for a specific protein or characteristic is called a gene
• In the cell cycle, cells divide in a series of stages. The genetic material is doubled and then divided into two identical cells
• The stages of mitosis are:

  Stage 1 - Growth

  Stage 2 - DNA Synthesis

  Stage 3 - Mitosis
• Stage 1 of mitosis: Growth:

  Before a cell can divide it needs to grow and increase the number of sub-cellular structures such as ribosomes and mitochondria
• Stage 2: DNA Synthesis:

  The DNA replicates to form two copies of each chromosome
• Stage 3: Mitosis:

  One set of chromosomes is pulled to each end of the cell and the nucleus divides. Then the cytoplasm and cell membranes divide to form two cells that are identical to the parent cell
• Fill in the blanks:

  A) DNA replication

  B) Mitosis

  C) Two diploid cells

  
• Stem cells are undifferentiated cells within an organism. They can produce other stem cells that can then differentiate into many different types of cells
• Human embryo stem cells: can be cloned and made to differentiate into most different types of human cells
• Human adult stem cells: can form many (but not all) types of cells including blood cells
• Human stem cells can be used to help treat diseases like diabetes and paralysis
• Embryos produced by therapeutic cloning have the same genes as the patient. This means stem cells from the embryo are not rejected by the patient's body. This is why they can be used for medical treatments
• The risks of using stem cells range from things such as transfer of viral infections, rejection of the transplanted cells, and the possibility of the stem cells becoming cancerous
• Some people have objections to stem cell use for ethical and religious reasons
• Undifferentiated stem cells in plants are grouped together in structures called meristems
• The undifferentiated cells can then specialise e.g. root hair cell, xylem or phloem cells
• Stem cells from meristems in plants can be used to produce clones of plants quickly and economically
• Rare species of plants can be cloned using stem cells to protect from extinction
• Crop plants with special features, such as disease resistance, can be cloned by using stem cells to produce large numbers of identical plants for farmers