SPEC 4.1.2.3 • CELL DIVISION
Stem Cells
Undifferentiated cells with revolutionary medical potential — and the evaluate-pattern question that demands both science and ethics in one answer.
One Word, One Mark
Stem cell questions on Paper 1 turn on specific named terms. The 1-mark "name the tissue" question is a regular pattern — and a regular mark loss for students who write descriptions instead of named terms.
The Pattern
For "name the plant tissue" questions, mark schemes credit "meristem", "meristem tissue", or "meristematic tissue". They do not credit "root tip", "growing tissue", or "young plant cells" — these are locations or descriptions, not the named tissue. Same idea applies elsewhere: when the command word is "name", give the named term, not a description.
Why This Lesson
Stem cell questions test two specific words: "differentiate" (not "specialise") and "meristem" (not "root tip"). Plus an evaluate skill — pros AND cons in the same answer. In the next 10 minutes, we'll get the words and the structure right.
By The End Of This Lesson
Three skills — every one tested directly on Paper 1.
1. Define
Define a stem cell using mark-scheme wording, including the words "undifferentiated" and "differentiate".
2. Describe
Describe the three sources of stem cells (embryonic / adult bone marrow / plant meristem) and what each can become.
3. Evaluate
Evaluate the use of stem cells in medicine — covering both benefits AND risks, then reaching a balanced conclusion. (Spec skill WS 1.3.)
Spec Boundary
The spec explicitly states: "Knowledge and understanding of stem cell techniques are not required." You don't need to know how to extract or culture stem cells — only what they are, where they come from, what they can do, and the ethics.
What Is A Stem Cell?
The mark-scheme definition. Memorise the exact wording.
Stem cell — Spec 4.1.2.3
A stem cell is an undifferentiated cell of an organism, capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation.
Three Defining Features
Undifferentiated — they haven't yet become specialised for a specific job.
Can divide repeatedly by mitosis — to produce more stem cells.
Can differentiate — into specialised cells with specific functions.
Use "Differentiate" — Not "Specialise"
The named process is differentiation. Mark schemes explicitly state "ignore specialisation" when describing how stem cells become other cells. The product is a "specialised cell" — but the process is "differentiation."
The Three Sources
The spec names three sources of stem cells. Each can differentiate into a different range of cells.
SourceWhere fromCan differentiate into
Embryonic stem cellsHuman embryosMost types of human cell
Adult stem cellsAdult bone marrowMany types of cells, including blood cells
Plant stem cellsPlant meristem tissue (root and shoot tips)Any type of plant cell, throughout the life of the plant
Pattern To Notice
Range of cells each can become: embryonic = most types of human cell (the spec wording — they're highly flexible but not literally "any cell"), adult bone marrow = many types (only certain types like blood cells), plant meristem = any plant cell (and for the plant's whole life). Mark schemes test these distinctions directly.
Embryonic vs Adult Stem Cells
The two animal sources. The spec wants you to know what each can do — and the trade-off between them.
Embryonic Stem Cells
Source: human embryos.
Can become:most types of human cell. The spec phrasing: stem cells from human embryos can be cloned and made to differentiate into most different types of human cells.
Catch: using human embryos raises ethical and religious objections.
Adult Stem Cells
Source: adult bone marrow.
Can become:many types of cells including blood cells (red blood cells, white blood cells, platelets).
Catch:limited range — they can't, for example, become nerve cells.
Mark-scheme phrase
Embryonic: "stem cells from human embryos can be cloned and made to differentiate into most different types of human cells." Adult: "stem cells from adult bone marrow can form many types of cells including blood cells."
Plant Meristems
The plant-specific source — and the named term that mark schemes are strict on.
Meristem — Spec 4.1.2.3
A meristem is a region of unspecialised dividing cells found in the tips of roots and shoots. Meristem tissue can differentiate into any type of plant cell, throughout the life of the plant.
Where
Meristems are found in actively growing regions of the plant — most notably the root tips (producing new root cells) and shoot tips (producing new shoot cells and leaves).
Why It Matters
Because plant meristem cells can differentiate into any plant cell for the whole life of the plant, plants can keep growing throughout their lives. Most animals stop growing as adults — plants don't.
Named Term Required
The mark-scheme word is meristem (or "meristem tissue" / "meristematic tissue"). NOT acceptable: "root tip" (that's a location, not a tissue type), "growing tissue" (description, not the named term), "young plant cells" (description). When asked to name the tissue, write the named term.
Medical Uses Of Stem Cells
The spec names two conditions stem cells could treat — and one specific technique you must understand.
Diabetes
Stem cells could be made to differentiate into insulin-producing cells in the pancreas — replacing those destroyed in type 1 diabetes.
Paralysis
Stem cells could differentiate into nerve cells to repair damaged nerve tissue in the spinal cord — potentially restoring movement.
Therapeutic Cloning — The Mark-Scheme Concept
In therapeutic cloning, an embryo is produced with the same genes as the patient. Stem cells from this embryo are genetically identical to the patient — so they will not be rejected by the patient's immune system.
This is the "why" behind therapeutic cloning. Mark schemes regularly test this exact reasoning chain: same genes → not recognised as foreign → not rejected.
Spec Boundary
You don't need to know how therapeutic cloning is done (the technique). You only need to know what it is (an embryo with the patient's genes) and why it works (no rejection because same genes).
Plant Cloning Uses
The spec names two specific applications of plant meristem stem cells. Both are about producing identical plants quickly and economically.
1. Saving Rare Species
Stem cells from meristems can be used to clone rare plant species — protecting them from extinction. A few cells from a single rare plant can be grown into thousands of identical individuals.
2. Useful Crop Plants
Crop plants with useful features (such as disease resistance or high yield) can be cloned to produce large numbers of identical plants for farmers — increasing food production.
Mark-scheme phrase
"Stem cells from meristems in plants can be used to produce clones of plants quickly and economically" — for rare species (extinction prevention) or crop plants with special features (e.g. disease resistance).
Risks & Ethical Objections
The spec explicitly requires you to know the risks and objections. These are the "cons" half of every evaluate question.
Spec-Named Risk
Transfer of viral infection — cultured stem cells might carry viruses that infect the patient when transplanted. This is the risk explicitly named in the spec — make sure you can write this one.
Additional Accepted Risk
Tumour formation — stem cells that don't differentiate as planned may keep dividing uncontrollably, forming tumours. The spec doesn't name this directly, but mark schemes for evaluate questions commonly accept it as a valid risk.
Ethical & Religious Objections
Using human embryos as a source of stem cells destroys the embryo. Many people object on religious or ethical grounds, arguing the embryo has the potential to become a person.
Mark-scheme phrase
"The use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections."
Why These Matter For Evaluate Questions
Any evaluate question on stem cells will require you to weigh benefits against these risks. One-sided answers (all pros, or all cons) cap at half marks. Always cover both, then reach a balanced conclusion.
Worked Example — Evaluate Question
Higher Tier evaluate questions are the highest-mark questions on this topic. Four marks, requiring both sides + a conclusion.
A scientist is investigating the use of embryonic stem cells to treat patients with type 1 diabetes.
Evaluate the use of embryonic stem cells in this treatment.4 marks
📋 Pattern: Evaluate — advantage + explanation + disadvantage + conclusion
Strategy
Don't write everything you know. The mark scheme awards: 1 mark for an advantage, 1 mark for explaining it, 1 mark for a disadvantage, 1 mark for a balanced conclusion. Pick one strong point on each side. Save time. Score four.
Worked Example — Pros, Cons & Conclusion
One advantage, one explanation, one disadvantage, one conclusion. Each line maps to one mark.
✓ MP1 — Advantage
Embryonic stem cells can differentiate into insulin-producing cells, replacing those destroyed in type 1 diabetes.
✓ MP2 — Explanation
This could effectively cure a condition currently managed only with daily insulin injections — a long-term improvement in quality of life.
✗ MP3 — Disadvantage (pick ONE)
Option A (ethical): using human embryos as a source of stem cells raises ethical and religious objections, as the embryo is destroyed in the process.
Option B (scientific): there is a risk of viral infection being transferred from cultured stem cells, or of cells forming tumours if they don't differentiate as planned.
You only need ONE disadvantage to score MP3 — not both. Pick whichever you can write more confidently.
✓ MP4 — Conclusion
"The medical benefits of treating diabetes are significant, but the ethical concerns mean embryonic stem cells should only be used where consent and regulation are in place." A balanced conclusion — not "yes, definitely" or "no, never."
Worked Example — Mark Scheme Tick-Off
Four marking points. Map each line of your answer to one tick.
✓
MP1 (advantage): stem cells can differentiate into insulin-producing cells / treat the cause of diabetes
✓
MP2 (explanation): currently incurable / would replace daily injections / long-term cure rather than management
✓
MP3 (disadvantage): ethical / religious objections to use of embryos OR risk of viral infection OR risk of tumours
✓
MP4 (conclusion): balanced judgement that weighs the points raised — not a yes/no opinion
Mark-Scheme Cap
If your answer covers only advantages (or only disadvantages), the mark scheme typically caps you at 2/4. The "evaluate" command word means both sides + a judgement. This is non-negotiable.
The Big Lesson
Evaluate questions reward structure, not effort. A 4-line answer with one strong pro, one strong con, an explanation, and a conclusion will outscore a 10-line one-sided argument every time.
Practice Question
A scientist uses therapeutic cloning to produce stem cells for a patient who needs a new heart valve.
Explain why the new tissue produced from these stem cells would not be rejected by the patient's body.2 marks
MP1
The stem cells from the cloned embryo have the same genes as the patient.
MP2
So the new tissue is not recognised as foreign by the patient's immune system / the immune system does not attack the cells / the cells are not rejected.
⚠️
Lose-the-mark traps: writing "the cells are similar" (must be same genes); writing "the body accepts them" without explaining why; missing the causal link between same genes and no rejection.
Three Examiner Alerts
The three traps that cost the most marks on stem cell questions.
Alert 1 — Differentiate, Not Specialise
The named process by which stem cells become specific cell types is differentiation. Mark schemes explicitly state "ignore specialisation". The cell that results is "specialised" — but the process is "differentiation." Use the spec word.
Alert 2 — Meristem, Not "Root Tip"
When asked to name plant stem cell tissue, the answer is meristem (or "meristem tissue" / "meristematic tissue"). NOT acceptable: "root tip" (location), "growing region" (description), "young tissue" (description). When the question says name, give the named term.
Alert 3 — Evaluate Means Both Sides
The command word evaluate requires both benefits AND risks + a balanced conclusion. One-sided answers cap at half marks. Mark schemes reward structure: pro + explanation + con + conclusion. Same number of marks for less writing.
Common Errors That Cost Marks
Four wrong-vs-right pairs lifted directly from mark-scheme guidance.
✗ Wrong
"Stem cells specialise"Wrong process word — mark schemes ignore "specialisation".
✓ Right
"Stem cells differentiate"The spec/MS named process.
✗ Wrong
"Stem cells are in the root tip"Names location, not tissue type.
✓ Right
"Stem cells are in the meristem"Named tissue (which is in root + shoot tips).
✗ Wrong
"Stem cells become any cell"Not true for all sources.
✓ Right
"Embryonic = most types; adult = limited; meristem = any plant cell"Specify the source — different ranges.
✗ Wrong
"Embryonic stem cells are bad"One-sided — caps at half marks for evaluate.
✓ Right
"More flexible than adult, but raise ethical concerns"Balanced — both sides scored.
Three Things To Remember
The whole lesson, distilled to three takeaways.
1. The Definition
A stem cell is an undifferentiated cell that can divide and differentiate into specialised cell types. Use those two mark-scheme words: undifferentiated and differentiate.
2. The Three Sources
Embryonic (most human cell types — but ethical issues).
Adult bone marrow (many types, including blood cells — limited range).
Plant meristem (any plant cell, throughout the plant's life).
3. Therapeutic Cloning & Risks
Therapeutic cloning works because the embryo has the same genes as the patient → cells not rejected. Risks: viral transfer, tumour formation, ethical/religious objections. Evaluate questions need both sides + conclusion.
Final Word
Stem cell questions reward two things: precise terminology ("differentiate", "meristem") and balanced structure on evaluate questions. Both are easy to nail with practice. The marks are there for the taking.
Next: Lesson 1.06 — Diffusion
The first of three transport mechanisms in cells. The exact mark-scheme definition the exam wants — and the alveoli adaptations that come up nearly every paper.
Coming Up
The two-mark definition of diffusion — and the preposition trap that loses students the second mark.
The three factors that affect rate of diffusion (concentration gradient, temperature, surface area).
How to apply diffusion to gas exchange in alveoli — the classic application question.
Before You Move On
Practise writing the stem cell definition from memory, including the words "undifferentiated" and "differentiate". Then work the practice questions and end-of-lesson test for this lesson — the evaluate-pattern question is the highest-yield to master.
Next: One Word, One Mark