Prophase Nuclear membrane starts to break down Centrioles replicate and start to move to opposite poles Chromotids condense
Metaphase Chromatids move to the equator Line up randomly Centrioles produce spindle fibres
Anaphase Spindle fibres connect to centromere and start to contract Chromosomes move towards the poles
Telophase Chromosomes start to unwind Nuclear membrane starts to reform
Cytokinesis Cell divides into two by infolding of the plasma membrane in animal cells and formation of new cell wall and membrane in plant cells
When control mechanisms break down the cell starts to divide uncontrollably There is rapid mitosis and a tumour forms that has no function. Benign tumours do not spread from their point of origin Malignant tumours spread through the body and invade other tissues. This is called metastasis.
Mutagen or Carcinogen? A mutagen is any factor that causes a mutation in a gene, and so is called a mutagenic factor. Most mutations caused in this way cause the cell to self-destruct, or to be destroyed by the immune system.
Carcinogens – cancer causing factors, and so therefore are referred to as Carcinogenic factors. They cause mutations in the genetic make up of a cell, which are not immediately fatal or recognized by the immune system. Examples of these factors are: – Ionising radiation (radiation, UV, X-rays) – Chemicals like tar – Viral infections – Hereditory predisposition
Meiosis Diploid cell – contains two complete sets of chromosomes (2n) Haploid – contains one complete set of chromosomes (n) Sexual reproduction requires a reduction cell division so that two haploid nuclei can join to make a diploid zygote.