What Are Stem Cells and How Are They Used?

Stem cells are undifferentiated cells that can divide to produce more stem cells and can develop into specialised cells. They could be used in medicine to replace damaged cells and treat conditions such as diabetes and paralysis.

What is a stem cell?

An undifferentiated cell has not yet developed the structures needed for a particular function. Through differentiation, a stem cell can become a specialised cell, such as a blood cell or nerve cell.

There are two important sources of human stem cells:

• Embryonic stem cells can be cloned and made to differentiate into most types of human cell.
• Adult bone marrow stem cells can form several types of cell, including blood cells, but they cannot usually form as wide a range as embryonic stem cells.

How are stem cells used in medicine?

Scientists may be able to grow stem cells and make them differentiate into the specialised cells needed by a patient. These cells could then replace damaged or faulty cells.

For example, stem cells may potentially help:

• people with diabetes, by replacing damaged cells
• people with paralysis, by repairing damaged nervous tissue

In therapeutic cloning, an embryo is produced with the same genes as the patient. Stem cells taken from this embryo are genetically matched to the patient, so they are less likely to be rejected by the patient’s immune system.

Risks and ethical issues

Stem-cell treatments can have risks, including the possible transfer of viral infections. Some people also have ethical or religious objections to using human embryos because the embryo is destroyed when its stem cells are collected.

Common exam mistake: Do not describe every dividing cell as a stem cell. A stem cell must be undifferentiated and able to produce other cell types through differentiation.

Scope assumption: this answer is for AQA GCSE Biology Higher Tier, although this stem-cell content is assessed at both Foundation and Higher Tier.