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2.5.1Inquiry Process

Stem Cells — IB Biology HL Revision Notes & Topical Questions

5 min read 6 parts Lesson 60 of 160

📚 IB Biology HL Hub / Topical Revision
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Part 1 of 6Properties of Stem Cells

2.5.1 Stem Cells

Stem cells provide the cells needed for growth and repair.

Self-renewal
  • A stem cell can divide by mitosis again and again, producing copies of itself.
Differentiation
  • Daughter cells can develop into specialised cell types such as blood or muscle cells.
Undifferentiated
  • Stem cells are unspecialised and not yet committed to one function.
Niche
  • A stem cell niche is the microenvironment in which stem cells are maintained and regulated.
TypeCan becomeExample
TotipotentAll cell types and the whole organismZygote, early embryo cells
PluripotentNearly all body cell typesEmbryonic stem cells
MultipotentA limited range of related typesBone marrow stem cells

Part 2 of 6How Differentiation Happens

1
All cells in an organism contain the same genes.
2
Signals from the niche or surroundings change which genes are expressed.
3
Different genes being switched on leads to production of different proteins.
4
The proteins made determine the structure and function of the cell.
5
Once differentiated, most cells cannot return to being stem cells.

Part 3 of 6Uses of Stem Cells

Uses of Stem Cells
Bone marrow transplants
  • Haematopoietic stem cells replace the blood system in patients treated for leukaemia.
Stargardt disease
  • Stem cells have been used in trials to replace damaged retinal cells.
Research
  • Stem cells are used to study development and test new drugs.
Umbilical cord blood
  • Cord blood is a source of haematopoietic stem cells that can be stored.

Part 4 of 6Ethical Considerations

Embryos
  • Obtaining embryonic stem cells destroys an embryo, which some people consider unacceptable.
Consent
  • Adult stem cell donors must give informed consent.
Benefits
  • The potential to treat serious disease is a strong argument for research.
Alternatives
  • Adult and induced stem cells avoid some of the objections to using embryos.

Part 5 of 6Worked Example

Question Explain why a zygote is described as totipotent but a bone marrow stem cell is only multipotent.

  1. The zygote and the cells of the very early embryo can form every cell type,
    • including the cells of the placenta,
    • so they can give rise to a whole organism.
  2. Bone marrow stem cells have already switched off many genes during development.
  3. They can therefore form only the range of blood cell types.

Answer Totipotent cells can form a complete organism, while multipotent cells form only a limited set of related cells.

Part 6 of 6Exam Checklist & Tips

2.5.1 – Key Points for the Exam

  • Stem cell An undifferentiated cell that can divide repeatedly and differentiate.
  • Differentiation Development of an unspecialised cell into a specialised cell.
  • Totipotent Able to form all cell types of an organism.
  • Pluripotent Able to form most cell types of the body.
  • Multipotent Able to form a limited range of related cell types.

Common Mistakes

  • Saying that differentiated cells lose genes; they only switch genes on or off.
  • Confusing totipotent with pluripotent.
  • Believing all stem cells come from embryos.
  • Ignoring the ethical arguments on both sides.

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Cambridge 9700 AS Biology Core Formula

Magnification Triangle & Unit Conversion

Formula: M = I / A  ⇔  A = I / M  ⇔  I = M × A

Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.