Cell division

A stem cell is an undifferentiated cell that can develop into one or more types of specialised cell.

There are two types of stem cells in mammals: adult stem cells and embryonic stem cells. 

Stem cells can be cloned to produce large numbers of identical cells.

Adult stem cells: 

• found in specific parts of the body in adult and children, eg. bone marrow
• can only differentiate to form certain types of cells, eg. stem cells in bone marrow can only differenciate into types of blood cell
• advantages: fewer ethical issues- consent, its an established technique for treating diseases such as leukaemia, relatively safe to use, donors recover quickly.
• disadvantages: requires a donor- potential long wait, can only differentiate into certain types of specialised cells- able to treat fewer diseases

Embryonic stem cells 

• found in early human embryos (often taken from spare embryos from fertility clinics) 
• they can differentiate into any type of specialised cell in the body, eg. a nerve cell
• advanatges: can treat a wide range of diseases as can form any specialised cell, may be possible to grow whole replacement organs, usually no donor needed as they are obtained from spare embryos from fertility clinics
• disadvantages: ethical issues as the embryo is destroyed and each embryo is a potential human life, risk of transferring viral infections to the patient, newer treatment so relatively under researched 

Plant meristem 

• found in the meristem regions in the roots and shoots of plants
• can differentiate into all cell types- can be used to create clones of whole plants 
• advantages: rare species of plants can be cloned to prevent extinction, plants with desirable traits can be cloned, quick,  low-cost production of large numbers of plants
• disadvantages: cloned plants are genetically identical, easy to get disease