The uptake of water by plants is called water absorption. Water is absorbed from the soil mainly through root hairs. The absorbed water crosses a variety cells such as cortical cells, passage cells(endodermis), pericycle and xylem tubers to reach the leaves. In 1949, Kramer proposed that water is absorbed by two mechanisms: active absorption and passive absorption.
Active absorption involves symplast movement of water in root hairs. The water first enters the cell sap and then passes from one cell to another. Such type of movement where living protoplasm involved, is called symplast. In passive absorption water moves probably through the free spaces or apoplast of root. The apoplast path of water movement includes cell wall and intercellular spaces, which are fully permeable. The water can reach up to endodermis through apoplast but it moves through the endodermis by symplast.
Symplast vs Apoplast Transport
|It consists of non living parts of plant body, i.e., cell walls and intercellular spaces.||It consists of living parts of plant body, i.e., protoplasts connected by plasmodesmata.|
|There is little resistance in the movement of water.||Some resistance occurs in the movement of water through symplast|
|It is faster.||It is slightly slower.|
|Metabolic state of root does not affect apoplast pathway.||Metabolic state of root directly affects symplast pathway.|