cell division

• cell continuity means that all cells develop from pre-existing cells
• chromosomes are coiled threads of DNA (which form genes) and protein that become visible in the nucleus at cell division
• genes are a section of DNA that contains the instructions for the formation of protein
• A haploid cell has one set of chromosomes eg sperm cell
• a diploid cell contain 2 sets of chromosomes eg human cheek cell
• a homologous pair has 2 chromosomes of similar size with the same sequence of genes
• interphase is the time spent when a cell is not dividing.during this time chromosomes elongate, new organelles are being made eg mitochondria. chemicals, enzymes and protein is made and chromosomes duplicate
• mitosis is a form of nuclear division in which the nucleus divides to form 2 nuclei containing the same number of chromosomes with identical genes
• mitosis occurs in all somatic cells (anything but sex cells)
• mitosis happens in the root tip and shoot tip of plants (meristomatic tissue)
• mitosis happens in 4 main phases (Pour Me Another Tea)

  .Prophase

  .metaphase

  .Anaphase

  .Telephase
• prophase

  • at the end of interphase the chromosomes contract and become visible
  • each chromosomes appears as a double stranded chromosome
  • spindle fibres appear in the cytoplasm
  • nuclear mebrane and nuclelose start to break down
• metaphase

  • nuclei membrane and nucleolus are fully broken down
  • chromosomes line up along the equator of the cell
  • spindle fibres attach to each chromosome and hold them in place
• Anaphase

  • spindle fibers contract (centromere splits)
  • chromosomes are pulled to opposite ends of the cell
• Telephase

  • a new nuclear membrane forms around each set of chromosomes
  • chromosones elongate and become chromatin
  • nucleolus reform
  • spindle fibres break down
  • 2 nuclei form
• cancer is a group of disorders in certain cells that have lost the ability to control both the rate of mitosis and the number of times mitosis happens
• the causes of cancer are called carcinogenic eg smoking, UV rays
• meiosis is a form of nuclear division in which the nucleus divides to form 4 nuclei with only half the same number of chromosomes as the parent cell
• meiosis occurs during gamete formation