The big idea: A stem cell is an unspecialized cell that can do two special things:
it can divide to make more cells (self-renewal), and it can differentiate into one or more specialized cell types.
These two properties are exactly what doctors need to treat disease: stem cells can be grown in large numbers and then turned into the specific cells a patient has lost — for example new blood cells, nerve cells or skin cells.
- Stem cell
- An unspecialized cell that can keep dividing (self-renew) and can differentiate into one or more specialized cell types.
- Self-renewal
- The ability of a stem cell to divide by mitosis to produce more cells, including more stem cells, so the supply is not used up.
- Differentiation
- The process by which an unspecialized cell becomes a specialized cell with a particular structure and function.
- Therapeutic use
- Using stem cells to treat a disease or injury — usually by replacing cells that have been lost or damaged.
Two properties, one purpose: Whenever an exam asks why stem cells are useful, the answer comes back to the same two properties:
they divide (so you can make enough cells), and they differentiate (so those cells become the right specialized type).
Replace a lost cell type → you need cells that can multiply and then become that exact cell.
Free preview
This is the free notes preview
You're reading the free notes. Aimnova Pro unlocks the full study experience — and you can try it with your first topic free to keep:
- FlashcardsLock in vocabulary and key terms with spaced repetition.
- Practice questionsAnswer exam-style questions and get instant AI marking.
- Mock exams & past-paper vaultSit full mocks and see exactly how examiners award marks.
- Personalised study planA daily plan built around your exam date and weak areas.
Start Studying Free Full access to Aimnova Pro · cancel anytime
Many diseases happen because a particular specialized cell type is lost or damaged and the body cannot replace it.
Stem cells offer a treatment: they divide to make many new cells, then differentiate into the exact cell type that was lost, so the missing tissue can be replaced and its function restored.
| Property of a stem cell | What it means | Why it is useful in medicine |
|---|---|---|
| Self-renewal (divide repeatedly) | A stem cell divides by mitosis to make more stem cells, so the supply does not run out | A large number of new cells can be grown to replace many lost cells |
| Differentiation (become specialized) | A stem cell can turn into one or more specialized cell types (e.g. a nerve, blood or muscle cell) | The new cells can become the exact specialized cell type that the patient has lost |
The logic of stem-cell treatment: Think of it as a simple cause-and-effect chain:
a disease destroys a specialized cell → the patient is given stem cells → the stem cells divide to make many cells → those cells differentiate into the missing specialized cell → the tissue is replaced and its job is restored.
Example: in a disease that destroys the light-detecting cells of the eye, stem cells could divide and differentiate into new light-detecting cells to restore vision.
Where the stem cells come from: Stem cells for treatment come from two main sources, and the source matters:
Embryonic stem cells come from very early embryos and can become almost any cell type, so they are very flexible — but using an embryo raises ethical objections.
Adult (tissue) stem cells, such as those in bone marrow, can become only a few related cell types, but they raise far fewer ethical concerns because no embryo is used.
| Feature | Embryonic stem cells | Adult (tissue) stem cells |
|---|---|---|
| Where they come from | Very early embryos | Found in body tissues (e.g. bone marrow) |
| What they can become | Almost any cell type (pluripotent) — very flexible | Usually only a few related cell types (multipotent) — more limited |
| How easily obtained | Harder to obtain; the source is an early embryo | Can be taken from the patient or a donor |
| Main ethical concern | Using an early embryo, which would otherwise grow, raises ethical objections | Far fewer ethical objections — no embryo is used |
Why stem cells help (benefits)
- They divide to make many new cells
- They differentiate into the cell type that was lost
- They can replace damaged tissue the body cannot regrow
- They may treat diseases that currently have no cure
Why it raises concerns (issues)
- Embryonic stem cells come from an early embryo (ethical objection)
- Donor cells may be rejected by the patient's immune system
- A small risk the cells divide uncontrollably (tumours)
- Adult stem cells are more limited in what they can become
A memory hook: Divide and differentiate = treat. Stem cells multiply then become the missing cell.
And when you weigh up the treatment: benefit = replacing lost cells; issue = where the cells come from (an embryo raises the ethical objection).
Reading the result (data skill): Stem-cell results are a favourite for data questions. If a sample of stem cells is grown and the count of cells goes up and some become a named specialized cell type, the stem cells have done both jobs: they divided (numbers rose) and they differentiated (specialized cells appeared).
If numbers rise but no specialized cells appear, the cells divided but did not differentiate.
Never wonder what to study next
Get a personalized daily plan based on your exam date, progress, and weak areas. We'll tell you exactly what to review each day.
Try Free Study PlanYour first topic is free to keep • No credit card required
How this is tested: On Paper 1 a short question often gives a disease in which a particular cell type is destroyed and asks why stem cells are suitable to treat it — the marks come from the two properties: stem cells divide to make many cells and differentiate into the exact cell type that was lost.
On Paper 2 you may have to discuss or evaluate stem-cell therapy, weighing the therapeutic benefit against the ethical issue of using embryonic stem cells.
On Paper 1B a data question may show how many cells were produced, and ask you to conclude whether the stem cells divided and differentiated as expected.
IB-style question — why stem cells suit this treatment
An inherited disease gradually destroys the light-detecting cells at the back of a patient's eye, causing blindness. Explain why stem cells are suitable to treat this disease. [3]
How to score all three marks
- Start with division (self-renewal). Stem cells can divide (by mitosis) to produce a large number of new cells, so there are enough cells to replace the many that were destroyed.
- Add differentiation. Stem cells can differentiate into specialized cell types, so they can become new light-detecting cells — the exact cell type the disease destroyed.
- Link to restoring function. The new light-detecting cells replace the lost ones, restoring the eye's ability to detect light and so improving vision. (Mark 1: divide / self-renew. Mark 2: differentiate into the specific lost cell type. Mark 3: replace cells / restore function.)
Final answer
Stem cells can divide to make many new cells and can differentiate into new light-detecting cells — the exact cell type destroyed — replacing the lost cells and restoring vision.
Why this scores full marks: It uses both key properties — divide and differentiate — and ties them to the specific lost cell type, not a vague 'they help the eye'.
A common slip is naming only one property: 'they divide' alone earns one mark, but the differentiation into the correct specialized cell is what makes the treatment work.
| Therapeutic uses (benefits) | Ethical / practical issues (concerns) |
|---|---|
| Replace cells lost to disease or injury (e.g. blood, nerve or skin cells) | Embryonic stem cells are taken from an early embryo, which raises ethical objections |
| Repair tissue that the body cannot regrow on its own | Transplanted cells may be rejected by the patient's immune system if from a donor |
| Potentially treat conditions that currently have no cure | There is a small risk that the cells divide uncontrollably (tumour formation) |