Stem Cells & Differentiation

What is the order of organisation in multicellular organisms?

Specialised cells → tissues → organs → organ systems → organism

What is a specialised cell?

A cell adapted by structure to perform a specific function.

What is cell differentiation?

The process by which a cell becomes specialised by expressing some genes and not others.

Do all cells contain the same DNA?

Yes—except anucleate cells like erythrocytes and sieve tube elements.

Why do erythrocytes lack a nucleus?

To increase space for haemoglobin.

Why do erythrocytes need constant replacement?

They have a short lifespan (≈120 days) due to no nucleus/organelles.

How many erythrocytes are produced per day?

≈3 billion per kg per day.

What is the function of neutrophils?

Immune response; engulf pathogens.

Why are neutrophils replaced rapidly?

Short lifespan (≈6 hours); high turnover during infection.

How many neutrophils are produced per hour?

≈1.6 billion per kg per hour.

What are stem cells?

Undifferentiated cells capable of division and specialisation.

Why is stem cell division tightly controlled?

Too slow → ageing; too fast → tumours/cancer.

What is stem cell potency?

The range of cell types a stem cell can differentiate into.

What are totipotent stem cells?

Can form all cell types including extra-embryonic tissues; zygote and early embryo cells.

What are pluripotent stem cells?

Can form all tissue types but not a whole organism; found in early embryos.

What are multipotent stem cells?

Can form a limited range of cell types within a tissue; e.g. bone marrow stem cells.

Where are embryonic stem cells found?

In early embryos, initially totipotent then pluripotent.

What is a blastocyst?

Early embryo (≈7 days) containing pluripotent stem cells.

What are adult (tissue) stem cells?

Multipotent cells found in specific body tissues such as bone marrow.

Advantages of umbilical cord stem cells?

Easy to obtain, plentiful, no invasive surgery, no rejection by the donor later.

Where are plant stem cells found?

In meristems: apical meristems and vascular cambium.

What do stem cells in the vascular cambium produce?

New xylem and phloem cells.

Why are plant stem cells available throughout life?

Meristem cells remain pluripotent indefinitely.

List medical uses of stem cells.

Heart repair, type 1 diabetes, Parkinson’s, Alzheimer’s, macular degeneration, spinal repair, treating birth defects.

List non-medical uses of stem cells.

Burn treatments, drug testing, developmental biology research.

Why are embryonic stem cells ethically controversial?

Extraction often destroys embryos; debate over embryo rights.

Why do umbilical stem cells avoid ethical issues?

No embryo destruction; ethically acceptable.

Limitation of umbilical stem cells?

Multipotent, not pluripotent.

What are induced pluripotent stem cells (iPSCs)?

Adult cells genetically reprogrammed to act like pluripotent embryonic cells.

Advantage of iPSCs?

No embryo destruction and patient-specific—no rejection.

Why don't plant stem cells raise ethical concerns?

Plants are not considered to have the same moral status as human embryos.

Why do multicellular organisms need specialised cells?

To increase efficiency—groups of specialised cells perform functions better than single cells.

What determines the adaptations a specialised cell develops?

Its role in the tissue, organ and organ system.

What is a tissue?

A group of similar specialised cells working together to perform a function.

What is an organ?

A group of tissues working together to perform a function.

What is an organ system?

A group of organs working together to carry out major life processes.