cell division and stem cells

• chromosomes

  thread-like structures made of DNA and proteins that carry genetic information found in the nucleus of every cell
• what is the number of chromosomes in a cell?

  it varies between different species. the human body has 46, 23 pairs of chromosomes, they’re not identical as the allele can vary. Male = XY Female = XX
• role of the nucleus

  it serves both as the repository (where things are stored) of genetic information, and as the cells control centre, as it tells the cell what to do
• mutation

  a change in a gene/chromosome
• what happens if a mutation occurs?

  genetic variation, the sequence of amino acids will change, the protein will be different affecting the functioning or characteristics of the organism
• what is cell division used by?

  multicellular organisms for growth, repair, reproducation and replacement of old/damaged tissues
• two types of cell division

  Mitosis and meiosis.
• meiosis

  cell division occurring when gametes(sex cells) are formed producing for non-identical haploid gametes each with half the number of chromosomes as the parent cell, a single cell divides twice to produce 4 cells

  
• mitosis

  the division of the parent cell into two genetically identical daughter cells (the chromosomes replicate) number of chromosomes are the same in the mother and daughter cells

  
• when do cells divide

  when an organism grows organisms need to replace worn out cells or repair damaged tissues
• what is mitosis for?

  used to produce new body cells, plants and animals use mitosis to reproduce (asexual reproduction)
• what is meiosis for?

  to produce egg and sperm cells for sexual reproduction

  male gametes + female gametes = fertilised egg cells
• diploid

  The presence of two complete set of chromosomes in an organism cell with each parent, contributing a chromosome to each pair
• why do cells need to divide

  for our body to grow and for body tissues to renew itself
• result of cell division

  growth, repair and replacement of old or damaged cells and tissues
• mitosis V meiosis

  comparison

  
• haploid 


  the presence of a single set of chromosomes in a organisms cells, only the egg and sperm cells are haploid
• definition of stem cell

  an unspecialised and undifferentiated cell that has the ability to develop into other cells
• adult stem cells

  change into a narrower range of cells
• embryonic stem cells

  wider range of cells to change into
• positives of embryonic sc

  • great variety of cells to develop into = can treat diseases, repair damaged tissues

  • source of cell readily available from IVF
• negatives of embryonic sc

  • embryo has potential to develop into a human being destruction of embryo means destruction of potential life (ethical issue)

  • can be classified as farming human beings, as embryos might be created specifically to produce stem cells
• positives of adult sc

  • body will accept the cell with no rejection of tissues or organs, as they have been grown from their own cells

  • no moral or ethical issues
• negatives of adult sc

  • can only develop into certain organs and is unable to differentiate into as many different types of cell
• source of stem cells in plants

  meristems - growing points in the tips and shoots of roots
• sources of stem cells in animals

  adult stem cells - (normally tissue specific) e.g. from bone marrow, umbilical cord, babies teeth

  embryonic stem cells - from embryos leftover firm into vitro fertility treatment (IVF)
• comparison of embryonic and adult stem cells

  
• stem cells in plants

  
• what can stem cells be used for?

  to replace damaged or disease tissue and so have many medical applications
• why better to use our own stem cells?

  no rejection, no need to find a donor. No need for tissue typing, avoids the use of embryonic stem cells which raises particular ethical issues
• what is the result of uncontrolled mitosis?

  large mass of cell forms a tumour, if the tumour successfully invades other tissues in the body it causes cancer