Edexcel A Level (IAL) Biology -3.17 Stem Cells & Cell Potency- Study Notes- New Syllabus
Edexcel A Level (IAL) Biology -3.17 Stem Cells & Cell Potency- Study Notes- New syllabus
Edexcel A Level (IAL) Biology -3.17 Stem Cells & Cell Potency- Study Notes -Edexcel A level Biology – per latest Syllabus.
Key Concepts:
- 3.17 (i) understand what is meant by the terms stem cell, pluripotent and totipotent, morula and blastocyst
(ii) be able to discuss the ways in which society uses scientific knowledge to make decisions about the use of stem cells in medical therapies
Stem Cells & Their Medical Use
🌱 Introduction
Stem cells are unspecialised cells that can divide and differentiate into various types of specialised cells.
They play a major role in growth, repair, and development, and are key to modern medical therapies.
1. Key Terms & Definitions
| Term | Meaning | Example / Notes |
|---|---|---|
| Stem Cell | Undifferentiated cell capable of dividing and forming specialised cells. | Found in embryos, bone marrow, umbilical cord, etc. |
| Totipotent | Can form all cell types including embryonic and extra-embryonic (placental) cells. | Zygote, early morula cells. |
| Pluripotent | Can form all body cell types but not placental cells. | Embryonic stem cells from the blastocyst. |
| Morula | Solid ball of cells formed after several mitotic divisions of the zygote. | Early embryonic stage (day 3-4). |
| Blastocyst | Hollow ball of cells with an inner cell mass source of embryonic stem cells. | Forms about day 5 after fertilisation. |
2. Stages of Early Embryo Development
- Fertilisation → zygote (totipotent).
- Mitosis → 8-16 cell stage → morula.
- Morula develops a cavity → forms blastocyst.
- Inner cell mass of blastocyst → pluripotent stem cells (form all body tissues).
📘 Mnemonic: “Z-M-B” → Zygote → Morula → Blastocyst.
3. Types of Stem Cells (Based on Potency)
| Type | Potency | Can Differentiate Into | Example |
|---|---|---|---|
| Totipotent | All cells (including placenta) | Any embryonic + extraembryonic cells | Zygote |
| Pluripotent | Almost all body cells (not placenta) | Body tissues, neurons, muscles, etc. | Embryonic stem cells |
| Multipotent | Limited range of cells | Blood, bone, immune cells | Adult stem cells (bone marrow) |
| Unipotent | One type only | Specific cell type (e.g. muscle) | Muscle stem cells |
4. Medical Uses of Stem Cells
- Treat leukaemia via bone marrow stem cell transplant.
- Repair damaged spinal cord or heart tissue.
- Grow new organs or skin grafts for burns.
- Research on genetic diseases & drug testing.
📌 Potential Future Uses: Curing diabetes (β-cell regeneration), Parkinson’s, Alzheimer’s.
5. Ethical & Societal Decisions on Stem Cell Use
| Issue | Scientific View | Ethical / Societal Concern |
|---|---|---|
| Embryonic stem cells | Highly pluripotent, valuable for research | Involves embryo destruction → moral issue |
| Adult stem cells | No ethical issue, used in therapy | Hard to isolate, limited potential |
| Induced pluripotent stem cells (iPSCs) | Adult cells reprogrammed → pluripotent | Avoids embryo use → more ethical |
| Legal/Religious decisions | Regulated or restricted embryo research | Debates on when life begins |
📘 Example: Some countries allow embryo use up to 14 days (before the nervous system forms).
6. Society’s Role in Decision-Making
- Uses scientific evidence + ethical reasoning to make laws and policies.
- National ethics committees review research proposals.
- Public discussions & regulations ensure responsible use.
- Balance: Use science to save lives while respecting moral values.
⚡ Quick Recap
Stem cells = undifferentiated, self-renew + differentiate.
Totipotent → all cells including placenta (zygote).
Pluripotent → all body cells (blastocyst inner mass).
Morula = solid ball; Blastocyst = hollow ball of cells.
Used in therapy, regeneration, and medical research.
Society balances science with ethics.
iPSCs = ethical alternative to embryonic stem cells.