How do roots absorb water? Explain the pathways by which water reaches the xylem.

1. 1 · Open in one line. Plants absorb water from the soil mainly through root hairs, by osmosis.
2. 2 · Root hair. An outgrowth of an epidermal cell, with a thin wall, a large vacuole of concentrated cell sap and a huge surface area.
3. 3 · Draw the path. [Soil particles with water, root hair, cortex cells, endodermis with Casparian strip, pericycle, xylem; one arrow along the cell walls (apoplast) and one through the cytoplasm (symplast)]
4. 4 · Processes.
   • Osmosis: water enters the root hair from dilute soil water.
   • Diffusion: movement from higher to lower concentration.
   • Active transport: minerals are taken in against the gradient using ATP.
5. 5 · Pathways.
   • Apoplast: through cell walls and intercellular spaces; blocked by the Casparian strip.
   • Symplast: through the cytoplasm and plasmodesmata.
6. 6 · Real life. Too much salt or fertiliser in the soil pulls water out of the roots, so plants wilt.
7. 7 · Close in one line. So water passes from the soil to the xylem, ready to rise up the plant.

Scoring tip: Draw one root section with two arrows of different colours, one for each pathway; one figure then explains both.