Totipotent cells are cells that can mature into any body cell. During development, totipotent cells translate only part of their DNA, resulting in cell specialistation. In mature plants, many cells are totipotent. They have the ability to develop in vitro into whole plants or into plant organs when given the correct conditions. Totipotent cells occur only for a limited time in mammalian embryos. Multipotent cells are found in mature mammals. They can devide to form only a limited number of different cell types. Totipotend and multipotent stem cells can be used in treating some genetic disorders. Candidates should be able to - interpret data relating to tissue culture of plants from samples of totipotent cells - evaluate the use of stem cells in treating human disorders.

All cells in an organism have the same DNA. However, different cells use different parts of the DNA, for example beta cells in the pancreas translate the part of DNA that makes insulin, but other cells do not. This is because cells are specialised for specific functions.

There are cells that are not specialised, and thus can use all of their DNA:

• Embryonic stem cells
• Adult stem cells: in the small intestine, skin and bone marrow
• Most plant cells

These cells are known as totipotent because of their ability to mature into any kind of cell. They do this by only translating some of their DNA and so only producing proteins for a specific function, resulting in specialisation.

Mature mammals also have multipotent cells which are able to specialise, but only into certain cells.

A cell from a plant can be grown in vitro, this means outside a living organism, in a nutrient medium with chemical stimuli, into a new plant or organ because of their totipotency.

Totipotent and multipotent cells can be used to create tissue to repair damage caused by disease or other medical issues by using growth factors to make them differentiate, for example red blood cells could be grown to treat leukaemia or beta cells could be grown to help someone with diabetes. There are different growth factors which are have different effects depending on concentrations and combinations.

Embryonic stem cells have be found more useful as they are easier to manipulate, however, there are ethical issues with using embryonic stem cells in this way:

• Some people consider embryos to be living things
• Research in that area could lead to cloning or people choosing the genetics of their babies

Arguments in defence are that:

• Embryos are just cells and not life
• There are laws prohibiting cloning and 'designer babies' in the UK so that is not a problem]
• It is wrong to continue to let people suffer when they could be treated as a result of stem cells