Stem cells

A stem cell is an unspecialised cell that can divide and produce cells that become specialised for particular functions. Specialisation gives a cell the structures and characteristics it needs for its role.

Stem cells divide by mitosis. Before division, the cell copies its genetic information. Mitosis then produces two daughter cells with the same genetic information as the original cell.

A daughter cell can become specialised through differentiation. During this process, different genes become active, causing the cell to develop the structures needed for a particular function. Cells can therefore have the same genetic information but develop different specialised roles.

Embryonic and adult stem cells

Stem cells can divide to produce new cells. They can also differentiate: develop into specialised cells with particular structures and functions.

Embryonic stem cells

Embryonic stem cells contribute to the growth and development of an embryo. They can differentiate into most types of human cell, providing the different specialised cells needed as the embryo develops.

These stem cells can be cloned to produce genetically identical stem cells, which can then be made to differentiate into different cell types.

Adult stem cells

Adult stem cells provide new cells in particular tissues. They generally have a more limited range of differentiation than embryonic stem cells: they can form only certain types of specialised cell.

For example, stem cells in bone marrow can form several types of cell, including blood cells.

Stem cell therapy

Stem cells can divide and develop into specialised cells. In stem cell therapy, they may be used to replace damaged cells or restore their function. For example, researchers are investigating whether stem cells can produce insulin-producing cells to help treat diabetes, or nerve cells to help treat paralysis. These are potential treatments, not guaranteed cures.

Therapeutic cloning

In therapeutic cloning, an embryo is produced with the same genes as the patient. Stem cells taken from the embryo are therefore genetically matched to the patient and are not rejected because of a genetic mismatch. They may be developed into specialised cells for treatment.

Risks and objections

Stem-cell treatment carries risks, including the possible transfer of a viral infection with the cells. Some people also have ethical or religious objections to using embryos to obtain stem cells, because obtaining the cells can involve destroying the embryo.

Plant meristem stem cells

Plants grow by producing new cells throughout their lives. These new cells come from regions of tissue called meristems, which contain stem cells. Meristem stem cells divide to produce more cells. The new cells can then differentiate, developing the structures and functions needed for different roles in the plant.

Meristem cells can differentiate into any type of plant cell. They therefore supply the cells needed for plant growth throughout the plant’s life.

Cloning plants using meristem cells

Meristem cells can be used to produce clones: plants that are genetically identical to the original plant. Cells from a plant’s meristem are grown to produce new plants. Because the cells can divide and differentiate, each new plant can develop the different cell types it needs.

This method can produce many plants quickly and economically. It can help protect rare species from extinction by increasing their numbers. It can also produce large numbers of identical crop plants with desirable features, such as disease resistance.