Stem cells
What is a stem cell?
A is an unspecialised cell that can do two things most cells can't: divide over and over to make more cells (self-renewal), and — develop into one or more specialised cell types, such as a nerve or blood cell.
How many different cell types a stem cell can become depends on where it comes from: embryonic, adult, or (in plants) meristem stem cells.
Key terms
Embryonic, adult and meristem stem cells
come from early embryos. They are the most versatile — they can differentiate into almost any cell type in the body.
are found in certain tissues, such as bone marrow. They can only differentiate into a limited range of cells — bone marrow stem cells make new blood cells.
are found in the growing tips of plant roots and shoots. Unlike most animal cells, they can differentiate into any type of plant cell throughout the plant's life.
Key terms
Uses of stem cells
Stem cells are used to treat some medical conditions, replacing cells damaged by disease or injury — for example, using to produce an embryo with the same genes as a patient, so any stem cells taken from it are not rejected by the patient's immune system. Potential uses include making insulin-producing cells for diabetes and nerve cells for paralysis.
In plants, meristem stem cells are used to clone whole plants quickly and cheaply — useful for preserving rare species or growing disease-free crops.
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Risks and ethical issues
Embryonic stem cells raise ethical concerns: obtaining them destroys the embryo, and some people believe an embryo has a right to life. Using stem cells in treatment also carries risks: they could transfer a viral infection, or divide in an uncontrolled way and cause cancer once transplanted.
Adult stem cells avoid the ethical issue around embryos, but are harder to obtain and can only become a limited range of cell types, which limits their medical use.