5.1.5—Stem cells

A stem cell is an undifferentiated cell that can divide by mitosis and produce a daughter cell that remains a stem cell or a daughter cell that differentiates into a specialised cell. Potency describes the range of specialised cell types it can produce.

• Self-renewal: A stem-cell division can maintain the stem-cell pool, so suitable stem cells remain available for future replacement and repair.
• Differentiation: A daughter cell can become specialised, changing gene expression and cell function to fit a tissue role rather than simply becoming larger.
• Potency: Multipotent adult stem cells can produce a limited range of related cell types. For example, bone-marrow stem cells can produce several blood-cell types.
• Adult source and use: Small populations of adult stem cells remain in tissues such as bone marrow, skin or gut and can contribute to normal cell replacement and tissue repair.
• Therapy boundary: Introducing suitable adult stem cells into damaged tissue is a research-based treatment opportunity for some diseases or injuries, but outcome depends on correct tissue matching, differentiation and control of the cells.
• Evidence boundary: The mapped SME/syllabus evidence here supports multipotent adult stem cells. It does not establish an embryonic-stem-cell source/use comparison, so no embryonic claim or ethical conclusion is added.

Self-renewal preserves a reservoir; differentiation converts some descendants into the specialised cells needed by a tissue. Together these properties explain how stem cells can support growth, routine replacement and repair, while limited potency and the need to control cell fate set boundaries on therapeutic use.

Stem cells are not all equally potent, and “can divide repeatedly” does not mean that every stem cell can make every cell type or that a therapy is automatically safe or effective. A differentiated cell is not automatically a stem cell again; tumour formation and uncontrolled division are handled separately in card 4565.