2.5.1Inquiry Process
Stem Cells — IB Biology HL Revision Notes & Topical Questions
5 min read 6 parts Lesson 60 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 6Properties of Stem Cells
Stem cells provide the cells needed for growth and repair.
Self-renewal
- Self-renewal A stem cell can divide by mitosis again and again, producing copies of itself.
Differentiation
- Differentiation Daughter cells can develop into specialised cell types such as blood or muscle cells.
Undifferentiated
- Undifferentiated Stem cells are unspecialised and not yet committed to one function.
Niche
- Niche A stem cell niche is the microenvironment in which stem cells are maintained and regulated.
| Type | Can become | Example |
|---|---|---|
| Totipotent | All cell types and the whole organism | Zygote, early embryo cells |
| Pluripotent | Nearly all body cell types | Embryonic stem cells |
| Multipotent | A limited range of related types | Bone marrow stem cells |
Section 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.
Section 3 of 6Uses of Stem Cells
Uses of Stem Cells
Bone marrow transplants
- Bone marrow transplants Haematopoietic stem cells replace the blood system in patients treated for leukaemia.
Stargardt disease
- Stargardt disease Stem cells have been used in trials to replace damaged retinal cells.
Research
- Research Stem cells are used to study development and test new drugs.
Umbilical cord blood
- Umbilical cord blood Cord blood is a source of haematopoietic stem cells that can be stored.
Section 4 of 6Ethical Considerations
Embryos
- Embryos Obtaining embryonic stem cells destroys an embryo, which some people consider unacceptable.
Consent
- Consent Adult stem cell donors must give informed consent.
Benefits
- Benefits The potential to treat serious disease is a strong argument for research.
Alternatives
- Alternatives Adult and induced stem cells avoid some of the objections to using embryos.
Section 5 of 6Worked Example
Question Explain why a zygote is described as totipotent but a bone marrow stem cell is only multipotent.
- 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.
- Bone marrow stem cells have already switched off many genes during development.
- 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.
Section 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.