CB2.2 — Stem cells (Edexcel 1SC0)

A stem cell is an undifferentiated cell that can divide and differentiate into specialised cell types.

Types of stem cells

Embryonic stem cells: found in the early embryo; can differentiate into almost any cell type (pluripotent). Harvesting them destroys the embryo — raises ethical objections.

Adult stem cells: found in specific tissues (e.g. bone marrow makes blood cells). More limited in what they can become (multipotent). No ethical issues with harvesting.

Meristems (plants): regions of unspecialised cells at root and shoot tips; produce all plant tissues. Used in cloning plants (tissue culture).

Therapeutic uses

• Bone marrow transplants: adult stem cells from a donor treat leukaemia (blood cancer).
• Skin grafts: stem cells used to grow replacement skin.
• Potential future uses: growing replacement organs or nerve cells for spinal cord injuries.

Ethical issues with embryonic stem cells

• Embryo is destroyed during harvesting → some argue this is killing a potential person.
• Could advance treatment of serious diseases.
• IVF spare embryos could be used → ethical debate about their status.

Differentiation

During development, genes are selectively switched on or off → cells become specialised. Once differentiated, most cells cannot revert. Plants retain the ability to differentiate throughout life; animals lose most of this ability as they mature.