Root hair cell

In the syllabus and the exam

Root hair cell is examined as the entry point of the whole water transport pathway, and it is one of the clearest structure-to-function examples tested under transport in plants. Candidates must state that each root hair cell has a long, thin, tubular extension that pushes out between soil particles, dramatically increasing the surface area available for absorbing water and dissolved mineral ions from the soil. Because the water potential inside the root hair cell is normally lower than that of the surrounding soil water, water enters the cell by osmosis, while dissolved mineral ions may be absorbed by active transport if their concentration in the soil is lower than inside the cell. Structured questions often ask candidates to explain why root hair cells lack chloroplasts, expecting the answer that they are located underground where no light reaches them and therefore have no functional need for photosynthesis. A common error is describing root hair cells as absorbing water by diffusion rather than osmosis, or forgetting to mention active transport when the question specifically asks about mineral ion uptake rather than water uptake. Candidates should also be aware that root hair cells are relatively short-lived structures that are continuously replaced near the growing root tip as older parts of the root mature and lose their root hairs, a detail occasionally tested when comparing the youngest and oldest regions of a root. This is also why transplanting a seedling carelessly, damaging its fine root hairs, often causes visible wilting even when the main root system remains largely intact, since most water absorption depends specifically on this delicate surface rather than on the thicker root beneath it.

Example

Explaining water absorption, a candidate writes: 'Root hair cells have a long, thin extension that greatly increases the surface area in contact with soil water, allowing water to move in by osmosis down a water potential gradient.'

Related terms

OsmosisXylemTranspiration stream

Source:SRC-DSKP-EN