Stem Cells

This lesson covers stem cells — what they are, where they are found, their potential uses and the ethical issues surrounding them — as required by the AQA GCSE Combined Science Trilogy specification (8464).

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What Are Stem Cells?

A stem cell is an undifferentiated cell that has the ability to:

1. Divide by mitosis to produce more stem cells (self-renewal).
2. Differentiate into one or more types of specialised cell.

Stem cells are the source of all the specialised cells in the body. They are critically important for growth, development and repair.

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Types of Stem Cell

There are different types of stem cell, which vary in their ability to differentiate:

1. Embryonic Stem Cells

• Found in early-stage embryos (typically at the blastocyst stage, a few days after fertilisation).
• Can differentiate into any type of cell in the body — they are described as pluripotent (or sometimes totipotent at the very earliest stage).
• Extremely versatile and are of great interest to medical researchers.

2. Adult Stem Cells

• Found in specific locations in the body of an adult organism (e.g. bone marrow, skin, brain, gut lining).
• Can differentiate into a limited range of cell types — they are multipotent.
• For example, bone marrow stem cells can produce different types of blood cell (red blood cells, white blood cells, platelets) but cannot produce nerve cells or muscle cells.

3. Meristems (Plant Stem Cells)

• Found in the meristems — regions at the tips of roots and shoots in plants.
• Can differentiate into any type of plant cell throughout the plant's life.
• Plants retain the ability to grow and produce new tissues indefinitely.

Type	Where Found	Differentiation Ability	Term
Embryonic	Early embryo	Any cell type	Pluripotent
Adult	Bone marrow, skin, brain, etc.	Limited range	Multipotent
Meristem	Tips of roots and shoots (plants)	Any plant cell type	Totipotent

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Uses of Stem Cells in Medicine

Stem cells have enormous potential for treating diseases and conditions:

Current Uses

Treatment	How It Works
Bone marrow transplant	Adult stem cells from bone marrow are transplanted to treat blood cancers (leukaemia) and blood disorders (e.g. sickle cell disease). The transplanted stem cells produce healthy blood cells.
Skin grafts	Stem cells are used to grow new skin for burns victims.

Potential Future Uses

Potential Treatment	How It Could Work
Repairing damaged nerve tissue	Embryonic stem cells could be directed to differentiate into new nerve cells to treat spinal cord injuries or paralysis.
Treating diabetes	Stem cells could be made to differentiate into insulin-producing beta cells to replace those destroyed in Type 1 diabetes.
Treating heart disease	Stem cells could differentiate into heart muscle cells to repair damage after a heart attack.
Treating Alzheimer's disease	Stem cells could replace damaged brain cells.

graph TD
    A["Stem Cells"] --> B["Embryonic Stem Cells<br/>(pluripotent)"]
    A --> C["Adult Stem Cells<br/>(multipotent)"]
    A --> D["Plant Meristem Cells<br/>(totipotent)"]
    B --> E["Potential: any cell type<br/>Nerve, muscle, blood..."]
    C --> F["Limited: related cells<br/>Blood cells from<br/>bone marrow"]
    D --> G["Any plant cell<br/>Root, leaf, flower..."]

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Therapeutic Cloning

Therapeutic cloning is a process where an embryo is produced that has the same genes as the patient:

1. The nucleus is removed from an egg cell (enucleation).
2. A nucleus from a patient's body cell is inserted into the egg cell.
3. The egg cell is stimulated to divide by mitosis, forming an embryo.
4. Embryonic stem cells are harvested from this embryo.
5. These stem cells have the same DNA as the patient, so they can be used without the risk of immune rejection.

Exam Tip: Therapeutic cloning is different from reproductive cloning. Therapeutic cloning aims to produce stem cells for treatment, not to produce a new organism. The AQA specification requires you to understand both the process and the ethical concerns.

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Ethical, Social and Religious Issues

The use of stem cells — particularly embryonic stem cells — raises significant ethical debates:

Arguments FOR Stem Cell Research

Argument	Explanation
Saves lives	Stem cell treatments could cure currently incurable diseases (e.g. Type 1 diabetes, Parkinson's, spinal injuries).
Embryos used would otherwise be destroyed	Many embryos used in research come from unused IVF embryos that would be discarded anyway.
Reduces suffering	Treating conditions like paralysis or heart disease would dramatically reduce human suffering.
Medical progress	Understanding stem cells leads to greater knowledge of how diseases develop and how the body works.

Arguments AGAINST Stem Cell Research

Argument	Explanation
Destroying a potential life	Some people believe that life begins at fertilisation and that destroying an embryo is morally equivalent to taking a life.
Religious objections	Some religious groups oppose the creation and destruction of embryos on moral or spiritual grounds.
Risk of tumour formation	Stem cells could divide uncontrollably and form tumours if not properly regulated.
Alternative sources exist	Adult stem cells can be used for some treatments, avoiding the ethical issues of using embryos.
Consent	The embryo cannot consent to being used for research.

Exam Tip: In exam questions about ethics, present both sides of the argument. State the argument clearly and explain the reasoning behind it. Do not just give your personal opinion — the marks are for demonstrating understanding of different perspectives.

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Plant Stem Cells (Meristems)

Plants have stem cells in regions called meristems, located at the tips of roots and tips of shoots (and in some cases in the cambium layer of the stem).

Uses of Plant Meristems

Use	Explanation
Cloning plants	Meristem cells can be used to produce clones of plants with desirable characteristics (e.g. disease resistance, high yield). This is called micropropagation or tissue culture.
Rapid production	Large numbers of identical plants can be produced quickly and cheaply.
Virus-free plants	Meristem tips are often free from viruses, so plants grown from them are healthy.
Rare species conservation	Rare or endangered plant species can be preserved by growing them from meristem tissue.

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Worked Example