Cell specialisation: root hair cells, xylem and phloem cells in plants.

The idea

Specialised plant cells have shapes and features matched to their jobs. A root hair cell has a long, thin extension that pushes between soil particles, giving a large surface area for absorbing water by osmosis and mineral ions by active transport; it has no chloroplasts because it is underground. Xylem cells are hollow tubes strengthened with lignin; they carry water and dissolved mineral ions upward from the roots and also support the stem. Phloem cells are living tubes with sieve plates and companion cells; they translocate dissolved sugars and amino acids up and down the plant. Comparing these three cells shows how structure links to function.

What earns the marks

• Root hair cells have a long, thin extension that increases surface area for absorption of water and mineral ions from soil.
• Root hair cells lack chloroplasts because they are underground and do not photosynthesise.
• Xylem cells are hollow, dead tubes strengthened with lignin that transport water and mineral ions upward and provide support.
• Phloem cells are living tubes with sieve plates and companion cells that translocate dissolved sugars and amino acids in both directions.
• Comparing the three cell types shows that each structure is adapted to its particular transport or absorption function.

Common mistakes and how to put them right

• Saying root hair cells absorb food from the soil.

  Put it right by stating they absorb water by osmosis and mineral ions by active transport.

• Confusing xylem and phloem direction.

  Put it right by stating xylem carries water and mineral ions upward only, while phloem carries dissolved sugars and amino acids up and down.

• Describing xylem as living cells.

  Put it right by stating xylem cells are dead and hollow, whereas phloem cells are living.

Exam tips

• Link each named cell to one clear function before adding structural detail.
• Use comparative language such as larger surface area, hollow and living when contrasting the three cell types.
• Sketch simple labelled diagrams of each cell to support written explanations.