📌Definition Table

Term	Definition
Stem cell	An undifferentiated cell capable of unlimited division and differentiation into specialised cells.
Differentiation	The process by which stem cells develop into specialised cells with distinct functions.
Potency	The capacity of a stem cell to differentiate into different cell types.
Totipotent	Stem cells that can form all embryonic and extra-embryonic cell types.
Pluripotent	Stem cells that can form any embryonic cell type but not extra-embryonic cells.
Multipotent	Stem cells that can differentiate into a limited range of closely related cell types.
Unipotent	Stem cells that can only divide into their own cell lineage.

📌Introduction

Stem cells are unique because they combine self-renewal with the potential to differentiate into other cell types. This makes them central to embryonic development and to adult tissue repair. Potency defines how versatile a stem cell is — totipotent cells have the greatest developmental potential, while unipotent cells are restricted to a single lineage. Understanding stem cells is vital for explaining how multicellular organisms grow, repair, and adapt.

📌 Stem Cell Niches

• Stem cells are maintained in specific “niches” — microenvironments that control their balance between self-renewal and differentiation.
• Bone marrow provides a niche for hematopoietic stem cells, enabling the continuous production of red blood cells, white blood cells, and platelets.
• Hair follicle niches ensure ongoing growth and regeneration of hair.
• Niches regulate stem cells by keeping them inactive until needed, or stimulating them when repair is required.
• The environment of the niche provides growth factors, cell-cell signals, and molecular cues that control stem cell fate.

🧠 Examiner Tip: Always remember the two hallmark properties of stem cells — self-renewal and differentiation. In exam answers, link potency terms (totipotent, pluripotent, multipotent, unipotent) to specific examples such as “bone marrow stem cells → blood cells.”

📌 Stem Cell Potency

• Totipotent cells (zygote and early embryonic cells up to 16-cell stage) can give rise to all embryonic and extra-embryonic tissues, including placenta.
• Pluripotent cells (embryonic stem cells) can form any embryonic tissue, but not extra-embryonic tissues.
• Multipotent cells (adult stem cells, e.g., in bone marrow) can differentiate into a limited but related group, such as all blood cell types.
• Unipotent cells (e.g., cardiomyocytes) can only divide to produce their own type, but still play a crucial role in tissue maintenance and repair.
• Potency is gradually lost as development progresses, reflecting increasing specialisation and loss of flexibility.

🧬 IA Tips & Guidance: Students could design investigations using model organisms such as planarians (flatworms) that demonstrate regeneration through stem cells, linking observations of regrowth to the concept of potency.

📌 Medical and Biological Significance

• Embryonic stem cells have immense potential for regenerative medicine, but raise ethical issues.
• Adult stem cells are used in therapies such as bone marrow transplants for leukaemia.
• Induced pluripotent stem cells (iPSCs) show how somatic cells can be reprogrammed to pluripotency, offering new therapeutic approaches.

🌐 EE Focus: An EE could explore the comparative effectiveness of embryonic stem cells versus iPSCs in regenerative therapies, or analyse ethical frameworks surrounding stem cell research

📌 Regenerative Potential

• Stem cells offer the possibility of replacing damaged tissues in diseases such as Parkinson’s, type I diabetes, or spinal cord injuries.
• Their ability to self-renew makes them suitable for long-term therapies, unlike transplanted differentiated cells that cannot divide indefinitely.

❤️ CAS Link: Students could create informational campaigns or workshops explaining stem cell therapies to the public, engaging in service learning while raising awareness of scientific and ethical issues.

📌 Ethics and Constraints

• Stem cell use raises ethical debates, particularly embryonic sources.
• Scientific advances such as iPSCs aim to resolve ethical dilemmas by avoiding embryo destruction.

🔍 TOK Perspective: The study of stem cells highlights tensions between scientific potential and ethical boundaries. It raises the TOK question: should knowledge always be pursued if it has potential benefits, even when ethical objections exist?

📝 Paper 2: Paper 2 may ask students to define and distinguish totipotent, pluripotent, multipotent, and unipotent cells, often requiring examples. Data-based questions may involve interpreting graphs of stem cell division or experimental results from regenerative research. To gain full marks, answers should connect potency levels to both developmental potential and practical applications.