5.1.55 · The Mitotic Cell Cycle

The Role of Stem Cells — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

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📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision

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5.1.5 The Role of Stem Cells — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Define stem cells, distinguish totipotent, pluripotent, multipotent and unipotent cells, and describe their use in medicine and the ethical issues involved.

Differentiation
Fate of new cells
Embryos and cord blood
Adult tissues
Bone marrow
Skin grafts

Part 1 of 8What stem cells are

Stem cell

Stem cell an undifferentiated cell that can divide by mitosis an unlimited number of times, either to self-renew or to differentiate into specialised cell types.

Differentiation

Differentiation every cell has the same genes, but a specialised cell expresses only some of them, because particular genes are switched on or off.

Potency

Potency the ability of stem cells to differentiate into more specialised cell types.

Fate of new cells

Fate of new cells each new cell can remain a stem cell or develop into a specialised cell such as a blood cell or muscle cell.

Part 2 of 8Types of stem cell by potency

Type	Can become	Example
Totipotent	Any cell type, including the placenta and the whole embryo	Zygote and cells of the very early embryo (up to the 8-cell stage in humans)
Pluripotent	Any cell type in the body but not extra-embryonic tissue	Embryonic stem cells from the blastocyst inner cell mass; induced pluripotent stem cells
Multipotent	A limited range of related cell types	Bone marrow stem cells, which form all blood cell types
Unipotent	Only one cell type	Epidermal stem cells producing skin cells; muscle satellite cells

Part 3 of 8Where stem cells are found

Embryos and cord blood

Embryos and cord blood stem cells are found in embryos and in umbilical cord blood.

Adult tissues

Adult tissues adult stem cells remain in bone marrow, skin, gut lining, heart and brain to produce new cells for growth, replacement and repair.
Most specialised adult cells gradually lose the ability to divide.
Adult (somatic) stem cells are usually multipotent.

Plants

Plants stem cells are found in meristems at the shoot and root tips and in the cambium, and stay capable of division throughout the life of the plant.

Part 4 of 8How stem cells differentiate

Signals

Signals signals from neighbouring cells, hormones and the physical environment make specific genes be transcribed.

Bone marrow

Bone marrow a multipotent haematopoietic stem cell divides and its daughters become red blood cells, neutrophils or lymphocytes, depending on the growth factors present.
Red blood cells lose their nucleus and fill with haemoglobin.

iPS cells

iPS cells differentiated cells usually cannot revert,
but induced pluripotent stem cells are made by introducing genes for certain transcription factors into adult cells, returning them to a pluripotent state.

Part 5 of 8Uses of stem cells

Bone marrow transplants

Bone marrow transplants they treat leukaemia and other blood disorders,
- because diseased marrow is destroyed and donor stem cells regenerate healthy blood.

Skin grafts

Skin grafts cultured epidermal stem cells treat burns.

Research

Research development studies and drug testing on tissues grown from stem cells.

Potential treatments

Parkinson's disease, type 1 diabetes, spinal cord injury and macular degeneration, by replacing lost cells.

Own cells

Own cells using the patient's own stem cells or iPS cells avoids immune rejection and reduces ethical problems.

Risks

Risks tumours may form if undifferentiated cells remain in the graft, and viruses can be transmitted from donors.

Part 6 of 8Ethical issues

Embryonic stem cells

Embryonic stem cells they come from embryos created by in vitro fertilisation, usually surplus ones, which are destroyed.

Against

Against an embryo has the moral status of a person from fertilisation, so its destruction is wrong.

For

For a blastocyst has no nervous system and has not yet the full status of a person,
- and the benefit to many patients justifies use with donor consent and strict regulation.

Alternatives

Alternatives adult and iPS cells avoid the issue, but adult cells give a limited range of cell types and iPS cells carry safety concerns.

Part 7 of 8Plants and cloning

Plants

Plants meristem tissue lasts throughout life, so a cutting can grow roots into a new plant.

Tissue culture

Tissue culture thousands of identical plantlets can be produced from a few cells grown on a sterile medium with hormones.

Therapeutic cloning

Therapeutic cloning a patient's nucleus is placed into an enucleated egg to give matching embryonic stem cells that avoid rejection,
but this raises further ethical concerns.

Part 8 of 8More from the specification

Interphase and the Cell Cycle

Interphase is the extended metabolic phase of the cell cycle consisting of G1, S,
and G2 stages, during which the cell grows, synthesises essential proteins,
and replicates its DNA so each chromosome consists of two genetically identical sister chromatids.

Telomeres and Chromosome Integrity

Telomeres are specialised non-coding repetitive DNA caps located at the ends of each eukaryotic chromosome that prevent degradation of coding sequences and stop chromosomes from fusing during successive replication cycles.

Cancer and Cell Cycle Checkpoints

Cancer is characterized by uncontrolled mitotic division triggered by genetic mutations in oncogenes and tumour suppressor genes, bypassing normal cell cycle control points.

Stem Cell Specialisation and Potency

Stem cells are unspecialised precursor cells capable of undergoing self-renewal through mitosis or differentiating into specialized functional cell lineages governed by selective gene expression.

Interphase and the Cell Cycle

Interphase is the extended metabolic phase of the cell cycle consisting of G1, S,
and G2 stages, during which the cell grows, synthesises essential proteins,
and replicates its DNA so each chromosome consists of two genetically identical sister chromatids.

Telomeres and Chromosome Integrity

Telomeres are specialised non-coding repetitive DNA caps located at the ends of each eukaryotic chromosome that prevent degradation of coding sequences and stop chromosomes from fusing during successive replication cycles.

Cancer and Cell Cycle Checkpoints

Cancer is characterized by uncontrolled mitotic division triggered by genetic mutations in oncogenes and tumour suppressor genes, bypassing normal cell cycle control points.

Stem Cell Specialisation and Potency

Stem cells are unspecialised precursor cells capable of undergoing self-renewal through mitosis or differentiating into specialized functional cell lineages governed by selective gene expression.

Organism

A living thing, such as a plant or an animal.

Genetically identical

Having the same alleles

Sister chromatids

The two identical DNA copies of a replicated chromosome joined at the centromere.

Multicellular organism

An organism made of more than one cell.

Asexual reproduction

Reproduction from one parent giving genetically identical offspring.

Malignant tumour

A rapidly growing tumour that invades tissues and may metastasise.

Chromatid

One of the two identical copies of a replicated chromosome.

Telomere

Repetitive non-coding DNA at the ends of a chromosome that prevents loss of genes during replication.

Interphase

The stage when the cell grows and DNA is replicated.

Protein

A long chain of amino acids containing carbon, hydrogen, oxygen and nitrogen.

Cancer

Disease in which cells divide uncontrollably and spread.

Chromosome

A thread-like structure of DNA carrying genes.

Replication

Exact copying of chromosomes before division.

Key terms

Term	Meaning
Stem cell	Undifferentiated cell that can self-renew and give rise to specialised cells.
Differentiation	Process by which a cell becomes specialised through selective gene expression.
Totipotent	Able to form all cell types including extra-embryonic tissue.
Pluripotent	Able to form all cell types of the body.
Multipotent	Able to form a limited range of cell types.
Meristem	Region of plant tissue containing dividing stem cells.
iPS cell	Induced pluripotent stem cell made from a differentiated cell.

Avoid these mistakes

Saying stem cells have different genes from specialised cells — they have the same genes, and the difference is in gene expression.

Confusing pluripotent with totipotent.

Treating all stem cells as embryonic — adult stem cells exist in tissues.

Giving only one side of the ethical debate.

Last updated: 15 October 2026