Knowledge Organiser: Stem Cells and Differentiation
Key Definitions
- Stem cell: Undifferentiated cell; can self-renew and differentiate
- Differentiation: Becoming specialised via switching genes on/off
- Embryonic SC: Pluripotent — can become any body cell
- Adult SC: Multipotent — limited to own tissue type
- Meristem: Plant stem cells at growing tips
How Differentiation Works
- All cells have identical DNA
- Different genes switched on/off
- Produces different proteins
- Gives different structure and function
- Generally irreversible in animals
Potency Hierarchy
- Totipotent: any cell (fertilised egg)
- Pluripotent: any body cell (embryonic SC)
- Multipotent: related cell types (adult SC)
- Unipotent: one cell type only
Medical Uses
- Bone marrow transplants (leukaemia)
- Skin grafts (burns)
- Potential: Parkinson's, diabetes, spinal cord
- Therapeutic cloning (Higher): genetically matched cells
Evaluate: Stem Cells in Medicine
- FOR: cure disease, replace tissue, no rejection (own cells)
- AGAINST: ethical (embryos destroyed), rejection risk, tumour risk
Memory Aid
- STEM = Specialisation Through Expression Modification
- Stem cells = blank clay; differentiation = firing in kiln
- DNA does NOT change — only gene expression changes
Common Mistakes
- Saying DNA changes during differentiation: DNA is identical in all body cells — only which genes are switched on/off changes, not the DNA sequence itself.
- Confusing pluripotent and multipotent: Embryonic stem cells are pluripotent (can become any body cell); adult stem cells are typically multipotent (limited to related cell types in their tissue).
- Saying adult stem cells can become any cell type: Most adult stem cells are multipotent — they cannot form all cell types like embryonic stem cells can.
- Forgetting plants retain differentiation ability: Unlike most animal cells, plant cells at meristems retain the ability to differentiate throughout the plant's life — this is a common exam distinction.
- Vague ethical arguments: For evaluate questions, name specific concerns (embryo destruction, religious objections, rejection risk) rather than writing "some people disagree with it."