Xylem tissue transports water and mineral ions from the roots to the stems…

The idea

Xylem is a transport tissue forming a continuous pipeline from root tips through stems to leaves. Root hair cells absorb water by osmosis and mineral ions by active transport, so the sap entering xylem is a dilute solution of ions such as nitrate, phosphate, magnesium and potassium. Once inside, water and dissolved ions move upwards as a column through hollow dead cells. This flow supplies photosynthesis in leaves with water and supplies growing regions with ions for making proteins, chlorophyll and other molecules. A useful method is tracing a labelled pathway: soil → root hair cell → root cortex → xylem → stem → leaf. Transpiration pull, driven by evaporation from leaves, draws the column upwards, while root pressure also contributes. Understanding this pathway explains why wilting, mineral deficiency and ringing experiments affect shoots.

What earns the marks

• Xylem is a plant transport tissue that carries water and dissolved mineral ions in one direction, from roots towards stems and leaves.
• Water enters root hair cells by osmosis because the soil solution is more dilute than the cell contents.
• Mineral ions such as nitrate, magnesium and phosphate are absorbed by active transport, requiring energy from respiration.
• Xylem forms a continuous pathway linking root, stem and leaf so that water and ions reach photosynthesising and growing cells.
• The upward movement occurs in the transpiration stream, driven largely by evaporation of water from leaf surfaces.
• Mineral ions are used in the plant, for example nitrate for amino acids and proteins, and magnesium for chlorophyll.

Common mistakes and how to put them right

• Saying xylem transports food or sugars.

  Put it right by stating that dissolved sugars are carried in phloem, while xylem carries water and mineral ions.

• Claiming mineral ions enter by osmosis.

  Put it right by explaining that ions are absorbed by active transport against a concentration gradient.

• Describing transport as two-way.

  Put it right by stating that xylem flow is essentially one-way, from roots to stems and leaves.

Exam tips

• Name the tissue, the substances carried and the direction of travel in one precise sentence to secure the transport point.
• Link each substance to its plant use, such as nitrate for proteins or magnesium for chlorophyll, to show understanding rather than recall alone.
• Use a labelled arrow diagram from root hair cell to leaf when a question asks you to trace a pathway.
• Distinguish absorption at the root from transport in the xylem, because marks are often awarded separately for each process.