Students should be able to explain how the structure of root hair cells,…

The idea

Root hair cells, xylem and phloem each show structural adaptations that suit their transport roles. A root hair cell has a long, thin extension that increases its surface area, so more water and mineral ions can be absorbed from the soil by osmosis and active transport. Xylem tissue is made of dead, hollow cells joined end to end and strengthened with lignin; this creates a continuous tube for water and mineral ions to move upward and helps support the plant. Phloem tissue contains living cells with sieve plates between them and companion cells; dissolved sugars are translocated from sources such as leaves to sinks such as roots, fruits and growing tips. Explaining adaptation means naming the feature, stating the function and linking the two.

What earns the marks

• Root hair cells have a long, thin extension that increases surface area for absorption of water and mineral ions from the soil.
• Root hair cells absorb water by osmosis and mineral ions by active transport, which requires energy from respiration.
• Xylem cells are dead and hollow and are joined end to end, forming continuous tubes that allow water and mineral ions to move upward.
• Xylem walls are strengthened with lignin, which supports the plant and helps withstand the tension of the water column.
• Phloem contains living cells with sieve plates and companion cells, enabling translocation of dissolved sugars from sources to sinks.
• The adaptations of each cell or tissue reduce resistance to flow or increase surface area, making transport more efficient.

Common mistakes and how to put them right

• Saying root hair cells absorb mineral ions only by osmosis.

  Put it right: Mineral ions are absorbed by active transport, while water is absorbed by osmosis.

• Describing xylem as living tissue.

  Put it right: Mature xylem cells are dead, leaving hollow tubes for water transport.

• Stating that phloem carries water.

  Put it right: Phloem translocates dissolved sugars, whereas xylem transports water and mineral ions.

Exam tips

• For each adaptation, write the feature, then its function, then how the function helps the plant, to build a complete explanation.
• Use precise transport terms such as osmosis, active transport and translocation rather than general words like 'moving'.
• If a question gives a diagram, refer to the visible feature, such as the hair-like extension or hollow tube, before explaining its advantage.