Preview
IB DP Biology — Form and Function | SL | B2.3 Cell Specialisation
📋 What You Will Learn
- Identify the key structural features of specialised cells including erythrocytes, neutrophils, sperm cells, egg cells, neurons, and muscle cells
- Explain how differential gene expression drives cellular differentiation from a single totipotent stem cell
- Analyse the relationship between a cell's structure and its specific function — applying the principle that form follows function
- Describe the properties and therapeutic potential of stem cells, distinguishing between totipotent, pluripotent, and multipotent categories
- Apply understanding of cell specialisation to unfamiliar cell types presented in exam data or micrographs
🔍 Guiding Question How does the expression of different genes in cells with the same genome lead to the enormous diversity of cell types found in multicellular organisms?
🌍 Why This Matters A single fertilised egg — one cell with one genome — gives rise to over 200 distinct cell types in the human body, from the transparent lens cells of the eye to the electrically excitable neurons of the brain. Understanding how this happens is the foundation of regenerative medicine: scientists are now reprogramming adult cells back into stem cells to grow replacement tissues for patients with heart disease, Parkinson's, and spinal cord injuries.
The Central Problem: One Genome, Two Hundred Solutions
Here is the problem every multicellular organism had to solve: how do you build a liver, a retina, and a bicep muscle from exactly the same set of genetic instructions? Every nucleated cell in your body carries an identical copy of your genome — roughly 20,000 protein-coding genes. Yet a pancreatic beta cell produces insulin while a neighbouring acinar cell produces digestive enzymes. The DNA is the same. The proteins are not.
The answer lies not in which genes are present, but in which genes are switched on. Differentiation is fundamentally a story about gene expression — about which chapters of the instruction manual each cell is allowed to read. Before we can understand how cells become specialised, we need the vocabulary to describe what is happening.
📖 Key Definition — Differentiation Differentiation is the process by which a cell develops a more specialised form and function through changes in gene expression, resulting in the production of specific proteins that give the cell its characteristic structure and activity.
📖 Key Definition — Gene Expression Gene expression is the process by which the information encoded in a gene is used to produce a functional product — typically a protein — through the processes of transcription and translation. Differential gene expression means different genes are expressed in different cell types, even though the genome is identical.
📖 Key Definition — Stem Cell A stem cell is an undifferentiated cell that retains the capacity to divide by mitosis and to differentiate into one or more specialised cell types. Stem cells are characterised by their potency — the range of cell types they can produce.
Stem Cells: The Undifferentiated Starting Point
Before a cell can become specialised, it must first be unspecialised. Stem cells occupy this remarkable position — they sit at the top of a developmental hierarchy, capable of both