Cell specialisation

What you need to know

• Specialised cells have a structure directly adapted to their function in a tissue, organ, organ system or whole organism.
• Sperm cells have a tail for swimming, many mitochondria to release energy for movement, and an acrosome containing enzymes in the head.
• Nerve cells have a long axon to carry electrical impulses over large distances and branched dendrites to connect to other cells; muscle cells have many mitochondria and protein fibres that can contract.
• Root hair cells have a long projection for large surface area; xylem forms hollow lignin-strengthened tubes for water transport; phloem cells have pores in end walls so dissolved sugars can pass from cell to cell.

The big picture

Cells become specialised during development so that their structure makes them exceptionally good at one specific function. Animal cells such as sperm, nerve and muscle cells each have unique structural features that directly enable their role. Plant cells such as root hair, xylem and phloem cells are equally specialised for absorbing and transporting materials through the plant. The key exam skill is always linking a structural feature to the function it enables.

Structure → Function connections

Tap each node to see what that feature does. Follow the links to see how each structural feature connects to its function.

Stop and predict

Commit to an answer before revealing — xylem and phloem features are easy to mix up.

A student describes xylem like this: 'Xylem cells have pores in their end walls so dissolved sugars can pass through.' How many errors does this description contain?

How plant cells are specialised for transport

Follow water and mineral ions from the soil, then trace how dissolved sugars move through the plant.

1. 1

   Water enters at root hair cells

   Root hair cells absorb water and mineral ions from the soil. Their long projection greatly increases the surface area, so more absorption can happen at the same time.

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2. 2

   Water and mineral ions enter xylem

   Once absorbed, water and mineral ions move into xylem vessels. The hollow tubes provide a continuous, unobstructed channel for transport through the plant.

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3. 3

   Dissolved sugars enter phloem

   Dissolved sugars are loaded into phloem cells and transported as cell sap to all parts of the plant that need them.

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4. 4

   Sugars move cell to cell through phloem

   Pores in the end walls of phloem cells (sieve plates) allow cell sap containing dissolved sugars to pass from one phloem cell to the next along the tube.

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Memory hook

Try 'SNM — RXP': Sperm, Nerve, Muscle (animal trio) then Root hair, Xylem, Phloem (plant trio). For each, ask one question: 'What is weird about this cell?' — the weird feature IS the adaptation.

Check yourself

Without looking — name one structural feature of a sperm cell, one of a nerve cell, and one of a phloem cell, then say what each feature enables the cell to do.