Uptake of water by root hairs
Plants constantly lose water by transpiration, and so root-hairs are responsible for the absorption of water to replace water that is lost.
Root-hair cells function for a few weeks before dying and being replaced by new cells, nearer the growing tip. They are efficient to exchange water and mineral ions because they a) provide a large surface area and b) have a thin surface layer so materials can move easily across.
As soil is mostly water so has a high water potential, water moves by osmosis into the root hair cells which have sugars and amino acids in them (this causes a lower water potential). This creates a water potential gradient, and water continues to move across the root by:
- Apoplastic pathway
- Symplastic pathway