1.2.3: Stem cells
Not started yet — this one needs some love.
Stem cell: undifferentiated cell that can (1) divide to produce more stem cells, and (2) differentiate into specialised cell types.
Embryonic stem cells: can differentiate into most human cell types (pluripotent); sourced from embryos.
Adult stem cells (bone marrow): can form blood cells and some other cell types.
Plant meristem tissue: located at growing tips (root and shoot); can differentiate into any plant cell type throughout the plant's life.
Therapeutic cloning: embryo with the patient's own genes is created → stem cells from this embryo will not be rejected by the patient's immune system.
Potential medical uses: treating diabetes, paralysis, and other conditions.
Risks: transfer of viral infections; ethical/religious objections to embryo destruction.
Plant uses: cloning rare species (conservation); producing identical disease-resistant crop plants.
Common exam mistakes
Embryonic stem cells → can become most cell types; adult (bone marrow) stem cells → mainly blood cells. Do not swap these.
Therapeutic cloning avoids rejection because the embryo carries the patient's own DNA — not simply because it is 'the same type of cell'. Be precise: the immune system recognises the cells as 'self'.
When asked about risks of stem cell therapy, 'the person might die' is too vague — state specific risks such as transfer of viral infections or uncontrolled cell division.
Plant meristems can differentiate into any plant cell — unlike adult animal stem cells.