Stem Cells

This lesson covers:

  1. What 'stem cells' are 
  2. The different types of stem cells
  3. Where stem cells are found in living organisms
  4. How stem cells can be used in research and medicine 

Stem cells

Multicellular organisms are made up of many different types of cells, each specialised for a particular function. However, all of these cells begin as unspecialised cells known as stem cells. 

Diagram showing the process of stem cell differentiation including mitosis and the formation of specialised cells such as red blood cells white blood cells and nerve cells.

Stem cells are undifferentiated cells that can develop into other types of cell. They are used by organisms for growth, development and tissue repair. 


Stem cells have two key features: 

  1. Stem cells can divide by mitosis to produce more undifferentiated cells. 
  2. Stem cells can differentiate into specialised cells.

Types of stem cells

Stem cells can be grouped into different types based on their ability to differentiate into different cell types, or their potency. The more cell types a stem cell can differentiate into, the greater its potency. 


There are four key types of stem cell: 

  1. Totipotent stem cells - These can differentiate into any cell type and go on to form whole organisms.
  2. Pluripotent stem cells - These can differentiate into most cell types, but cannot form whole organisms. 
  3. Multipotent stem cells - These can only differentiate into a few different cell types. 
  4. Unipotent stem cells - These can only differentiate into one type of cell. 

Locations of stem cells

Stem cells are found in early embryos, adults, and plants. 


Embryonic stem cells 

  • Found in the early stages of embryo development where they can differentiate into cells to form a foetus.
  • In the first few divisions of the embryo, the stem cells are totipotent.
  • After about 7 days, these stem cells become pluripotent.


Adult stem cells 

  • Found in some adult tissues where they can replace faulty cells.
  • Stem cells are multipotent or unipotent. 
  • Stem cells in the bone marrow replace worn out erythrocytes (red blood cells) and neutrophils (white blood cells). 


Plant stem cells 

  • Found in the meristematic tissue or meristems at the tips of the shoots and roots of plants.
  • Stem cells are pluripotent.
  • Meristematic tissue is also found between phloem and xylem tissues in an area known as the vascular cambium.
  • These stem cells differentiate into cells of the xylem and phloem.  

Stem cells in research and medicine

Since stem cells have the ability to differentiate into specialised cells, they have the potential to treat certain diseases. This works by using stem cells to replace faulty cells or tissues. 


Parkinson's and Alzheimer's are both neurological disorders caused by a loss of nerve cells in the brain. Transplanted stem cells could help to regenerate nerve cells and reduce symptoms of these conditions. 


Stem cells can also be used for the following purposes: 

  • Testing new drugs - Drugs can be tested for toxicity and side effects before being tested on humans. 
  • Studying development of organisms - Scientists can find out how organisms grow and develop from a single cell. 
  • Identifying causes of disorders - Scientists can identify when something goes wrong in an organism's development.