Question

Long answer question.

Write on journey of water from soil to xylem in roots.

Answer 1

1. Water is absorbed by root hair cells through processes like imbibition, diffusion, and osmosis which occur sequentially.
2.  Water passes through the epidermal cell (epiblema), cortex, endodermis, Casparian strip, pericycle and then to the protoxylem.
3. When root hair cell absorbs water it becomes turgid. Its turgor pressure increases, but its DPD value decreases.
4. However, the immediately adjacent cortical cell inner to it, has more DPD value because its O. P. is more.
5. Therefore, the cortical cells will absorb water from the turgid root hair cell. It then becomes turgid.
6. The flaccid root hair cell now absorbs water from the soil.
7. Water from the turgid cortical cell is absorbed by the inner cortical cell and the process goes on.
8. Thus, a gradient of suction pressure (DPD) is developed from cells of epiblema to the cortex of the root.
9. Consequently, water moves rapidly across the root through loosely arranged living cells of the cortex, followed by passage cells of endodermis and finally into the cell of the pericycle.
10. The protoxylem is in close proximity to the pericycle.
11. It is due to root pressure, that water from pericycle is forced into the xylem.
12. Pathway of water across the root occurs in two types: Apoplast pathway and Symplast pathway
13. Apoplast pathway: When some amount of water passes across the root through the cell wall and the intercellular spaces of cortical cells of the root, it is then called the apoplast pathway. This pathway occurs up to the endodermis.
14. Symplast pathway: When water passes across from one living cell to another living cell through plasmodesmata, then it is called the symplast pathway. It is also called the trans-membrane pathway.