B2 Cell Division

• What is a stem cell?

  cell that can turn into one or more specialised cells
• What are adult stem cells?


  adult stem cells can only turn into certain specialised cells
• Where can adult stem cells be found?

  bone marrow
• Where are embryonic stem cells found?

  early human embryos
• What is therapeutic cloning?


  patients' cells are used to create an early embryo clone of themselves. Stem cells from the embryo can then be used to treat the patient's medical conditions.
• Give one advantage of using adult stem cells

  fewer ethical issues as obtained from adults who can consent to their use
• Give two disadvantages of using adult stem cells

  1. can take a long time for a donor to be found 2. can only turn into some specialised cells so can treat fewer diseases
• Give two advantages of using embryonic stem cells

  1. can turn into any specialised cells can be used to treat many diseases 2. easier to obtain as they are found in spare embryos from fertility clinics
• Give two disadvantages of using embryonic stem cells

  1. ethical issues surrounding their use 2. potential risks involved with treatments such as transfer of viral infections
• What are plant meristems?


  area where rapid cell division occurs in the tips of roots and shoots
• Give two advantages of using plant meristems to clone plants

  1. rare species can be cloned to protect them from extinction 2. plants with special features (e.g. disease resistance) can be cloned to produce many copies
• Give one disadvantage of using plant meristems to clone plants

  no genetic variation so for example an entire cloned crop could be destroyed by disease
• What is cell division by mitosis?

  body cells divide to form two identical daughter cells
• What are two purposes of mitosis?

  1. growth and repair of cells 2. asexual reproduction
• What happens during the first stage of the cell cycle? (three things)

  1. cell grows bigger 2. chromosomes duplicate. DNA doubles 3. number of sub-cellular structures (e.g. ribosomes and mitochondria) increase
• What happens during mitosis (second stage of the cell cycle)?

  one set of chromosomes is pulled to each end of the cell and the nucleus divides
• What happens during the third stage of the cell cycle?

  the cytoplasm and cell membrane divide
• Before a cell divides it does three things...

  1. grows in size 2. increases the amount of subcellular structures 3. duplicates DNA
• Cell differentiation is...

  the process by which a cell changes to become specialised for its job
• What are embryonic stem cells?

  stems cells from embryos that can turn into any specialised cell