Plant organ system: Students should be able to explain how the structure of root hair cells, xylem and phloem are adapted to their functions.

The idea

Root hair cells, xylem and phloem each have structures matched to their jobs. A root hair cell has a long, thin extension that increases surface area for absorbing water and mineral ions from soil, plus a large vacuole and many mitochondria for active transport. Xylem tissue is made of dead, hollow cells joined end to end, forming continuous tubes with thickened walls; this lets water and mineral ions move upward with little resistance and supports the plant. Phloem tissue contains living cells with sieve plates and companion cells; dissolved sugars are loaded and transported to growing or storage regions.

For example: A root hair cell's surface area helps uptake, xylem's hollow tube allows rapid water flow, and phloem's companion cells provide energy for translocation.

What earns the marks

• Describes the root hair cell's long, thin extension as increasing surface area for absorption of water and mineral ions from the soil.
• Explains that root hair cells contain many mitochondria to release energy for active transport of mineral ions.
• Describes xylem as dead, hollow cells joined end to end to form continuous tubes that carry water and mineral ions upward.
• Explains that xylem walls are thickened with lignin, providing strength and helping the plant stay upright.
• Describes phloem as living tissue with sieve plates and companion cells that transports dissolved sugars around the plant.
• Links each adaptation to its function, for example surface area to absorption, hollow tubes to transport, and companion cells to energy for translocation.

Common mistakes and how to put them right

• Saying root hair cells absorb food from the soil.

  Put it right by naming water and mineral ions as the substances taken up.

• Describing xylem as living cells.

  Put it right by stating that xylem cells lose their contents as they mature.

• Confusing translocation with transpiration.

  Put it right by matching each term to its tissue and direction.

Exam tips

• For each adaptation, write 'because' to force a clear link between structure and function, such as 'large surface area because more water can be absorbed'.
• Use precise terms: surface area, active transport, lignin, sieve plates, companion cells and translocation.
• Compare xylem and phloem in a table with columns for living or dead, direction of transport and substances carried.