Stem Cells

GCSE Biology · Cell Biology

What Are Stem Cells?

Stem cells are undifferentiated cells that have the ability to divide and produce any type of specialised cell. They are unique because they can both self-renew (make copies of themselves) and differentiate (become specialised cells).

Types of Stem Cells

Type	Where found	What they can become
Embryonic stem cells	Early human embryos (up to about 7 days old)	Any cell type in the body — they are totipotent
Adult stem cells	Specific tissues, e.g. bone marrow	Only certain cell types — they are multipotent
Meristem cells	Tips of roots and shoots in plants	Any plant cell type

Embryonic Stem Cells

Embryonic stem cells are found in the inner cell mass of a blastocyst (an early-stage embryo). They can differentiate into virtually any cell type, making them extremely valuable for medical research.

Advantages:

Can produce any type of human cell
Could be used to treat a huge range of diseases and conditions
Large quantities can be grown in the lab

Disadvantages and ethical concerns:

Embryos are destroyed in the process — some people believe life begins at fertilisation and consider this morally wrong
Risk of tumour formation if cells divide uncontrollably
Risk of viral infection when transferring cells
The embryo cannot give consent

Adult Stem Cells

Adult stem cells are found in certain tissues throughout the body. Bone marrow contains stem cells that can produce different types of blood cell (red blood cells, white blood cells, platelets).

Bone marrow transplants are already used to treat conditions like leukaemia (a cancer of white blood cells). The patient's faulty bone marrow is destroyed and replaced with healthy donor stem cells.

Advantages:

No embryos are destroyed — fewer ethical objections
The patient's own cells can sometimes be used, reducing rejection risk
Already used successfully in medicine

Disadvantages:

Can only differentiate into a limited range of cell types
Harder to grow in large numbers in the lab
The extraction procedure can be painful

Therapeutic Cloning

Therapeutic cloning involves taking the nucleus from a patient's body cell and inserting it into an enucleated egg cell. The resulting embryo is genetically identical to the patient, so stem cells taken from it would not be rejected by the immune system.

This is different from reproductive cloning (which aims to produce a whole organism).

Plant Stem Cells — Meristems

Plants have stem cells in regions called meristems, found at the tips of roots and shoots. Unlike animal cells, many plant cells retain the ability to differentiate throughout the plant's life.

Meristem cells can be used to:

Produce clones of plants quickly and cheaply
Grow rare or endangered species in large numbers
Produce disease-free plants from a single healthy specimen

This process is called micropropagation or tissue culture.

Medical Uses of Stem Cells

Stem cells could potentially treat:

Type 1 diabetes — replacing damaged insulin-producing beta cells in the pancreas
Paralysis — regrowing damaged nerve cells in the spinal cord
Parkinson's disease — replacing lost dopamine-producing brain cells
Heart disease — repairing damaged heart muscle tissue
Leukaemia — bone marrow transplant (already in use)

Exam Tips

Know the difference between embryonic and adult stem cells — embryonic can become any cell type, adult can only become certain types
Ethical arguments are commonly examined — be ready to discuss both sides
Remember that plant meristem cells are equivalent to animal stem cells but raise fewer ethical concerns