What is a specialised cell? Structure, function and examples

Definition, and what questions actually ask

A specialised cell has a structure adapted to one particular role. A red blood cell carries oxygen; a root hair cell absorbs water; a neurone transmits impulses.

The definition is worth one mark at most. The marks sit in explaining the adaptation — and the word 'explain' means you must say <em>why</em> the structure helps, not just that it exists. 'Red blood cells have no nucleus' is a description. 'Red blood cells have no nucleus, leaving more room for haemoglobin so each cell carries more oxygen' is an explanation.

How specialisation happens

All cells in an organism carry the same genes. Differentiation is the process of switching some on and others off, so a cell makes only the proteins its role requires.

In animals, most cells differentiate early and cannot revert; adult stem cells remain in a few tissues such as bone marrow. In plants, many cells retain the ability to differentiate throughout life, which is why a cutting can grow into a whole plant.

Eight examples, with the link made explicit

Learn these as structure → why it helps, not as bullet points.

• Red blood cell — biconcave disc increases surface area for gas exchange; no nucleus leaves more space for haemoglobin; flexible so it can squeeze through capillaries.
• Root hair cell — long thin extension gives a large surface area for water and mineral uptake; no chloroplasts because it is underground and would not use them; many mitochondria for the active transport of minerals.
• Neurone — long axon carries impulses over distance; myelin sheath insulates so the impulse jumps between nodes and travels faster; dendrites give a large surface area for connections with other neurones.
• Sperm cell — flagellum for swimming; many mitochondria to supply that energy; acrosome carries enzymes to digest the egg membrane; haploid nucleus so fusion restores the diploid number.
• Palisade mesophyll cell — packed with chloroplasts for photosynthesis; tall and column-shaped so more can fit near the leaf surface; thin walls so carbon dioxide diffuses in quickly.
• Ciliated epithelial cell — cilia beat to move mucus and trapped particles out of the airways; many mitochondria to power that beating.
• Muscle cell — packed with actin and myosin filaments that slide past one another to contract; many mitochondria for the ATP that contraction consumes.
• Xylem vessel — hollow dead cells with no end walls form a continuous tube; lignified walls resist collapse under the tension of the transpiration stream.

Specialised cells, tissues, organs, systems

Specialised cells of one type form a tissue. Different tissues working together form an organ. Organs working together form a system.

Questions often ask you to place a named cell in this hierarchy: palisade mesophyll cell → palisade tissue → leaf → shoot system. Getting the order right is a common easy mark.

How to answer the exam question

Almost every question follows the same shape: name a feature, then explain how it helps the function.

Use the word 'so' or 'which means'. It forces the causal link that markers are looking for. 'The root hair cell has many mitochondria, which release energy for active transport, so minerals can be absorbed against a concentration gradient.'

If your sentence could stop after the feature and still make sense, you have described rather than explained, and the explanation marks are still unclaimed.