water uptakethe uptake of water into a plant through the roots. Water only enters the plant if there is a deficit in the XYLEM caused by losses during TRANSPIRATION. The path of water from soil to leaf is as follows:
- (a) movement of free soil water into the root hair by OSMOSIS;
- (b) across the CORTEX of the root towards the STELE, by one of three methods: (i) via cell walls and intercellular spaces by hydration; (ii) via PLASMODESMATA by CYCLOSIS. (iii) via cell vacuoles by osmosis;
- (c) through the endodermis (see CASPARIAN STRIP across the PERICYCLE and into the XYLEM VESSELS. These latter contain ions which are actively pumped into the xylem to raise the concentration of solutes, thus making the osmotic potential more negative;
- (d) up the plant in the xylem by a combination of: (i) TRANSPIRATION pull and cohesion-tension (see COHESION-TENSION HYPOTHESIS). (ii) capillarity (iii) ROOT PRESSURE.All water uptake is variable according to the plant, its age, environment and the time of year.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005