Key Specialised Cells and Their Adaptations
| Cell | Adaptations | How adaptations help |
|---|---|---|
| Red blood cell | Biconcave disc shape; no nucleus; contains haemoglobin | Biconcave shape increases surface area for O₂ absorption; no nucleus = more space for haemoglobin; haemoglobin binds O₂ |
| Root hair cell | Long, thin hair-like extension; large vacuole; thin cell wall | Hair extension increases surface area for water and mineral ion absorption from soil |
| Palisade mesophyll cell | Tall and columnar; packed with chloroplasts; near upper surface of leaf | Many chloroplasts for maximum photosynthesis; positioned where most light is absorbed |
| Sperm cell | Streamlined head; long tail (flagellum); many mitochondria in midpiece; acrosome | Tail propels sperm; mitochondria provide energy for swimming; acrosome contains enzymes to penetrate egg |
| Nerve cell (neurone) | Very long axon; branched endings (dendrites); myelin sheath | Long axon transmits impulses over distance; dendrites connect to other neurones; myelin sheath speeds up impulse transmission |
| Ciliated epithelial cell | Hair-like cilia on surface; many mitochondria | Cilia beat rhythmically to move mucus (trapping bacteria/particles) along airways |
| Xylem vessel | Dead, hollow, no end walls; lignified walls; long continuous tubes | No contents = unobstructed water flow; lignin strengthens and waterproofs; continuous tubes for efficient transport |
How to Answer "Explain the Adaptation" Questions
These questions follow a predictable three-part pattern:
- Name the adaptation: "Red blood cells have no nucleus."
- Link it to the function: "This provides more space for haemoglobin."
- Explain the benefit: "So they can carry more oxygen to respiring cells."
Always complete all three steps. Many students lose marks by naming the adaptation without explaining why it helps.
Differentiation and Stem Cells
Cells become specialised through differentiation: the process by which a cell develops specific structures and loses others. Once differentiated, most animal cells cannot change into another cell type.
The key exam link: stem cells are unspecialised cells that can differentiate into many cell types. This connects to the stem cells subtopic and has implications for medical treatments (replacing damaged cells in diseases).