If some solute is dissolved in pure water, solution has fewer free water molecules and the concentration of water decreases, reducing its water potential.
Hence, all the solutions have a lower water potential than pure water. The magnitude of this lowering is due to dissolution of solute is called solute potential or $\psi_s . \psi_s$ is always negative. The more the solute molecules, the lower (more negative) is the solute potential $\psi_s$ water potential of a cell is affected by both solute and pressure potential.
The relationship can be illustrated as
$$\begin{aligned} &\text { Where, }\\ &\begin{aligned} & \psi_w=\psi_s+\psi_p \\ & \psi_w=\text { water potential } \\ & \psi_s=\text { solute potential } \\ & \psi_p=\text { pressure potential } \end{aligned} \end{aligned}$$
An onion peel was taken and
(a) placed in salt solution for five minutes.
(b) after that it was placed in distilled water.
When seen under the microscope what would be observed in (a) and (b)?
(a) Onion peel when placed in salt solution, shrinks as water from cells cytoplasm moves out of the cell i.e., hypertonic solution.
(b) When it is placed again back in distilled water, cell regains it's shape and absorbs water and become turgid (full of water) i.e., hypertonic solution.
Difference between apoplast pathway and symplast pathway is as follows
Apoplast Pathway | Symplast Pathway |
---|---|
It consists of the non-living parts of plant body, i.e., cell walls and inter cellular spaces. There is a little resistance in the movement of water in apoplastic pathway. It is a faster process. |
It consist of living parts of plant body, i.e., protoplast connceted by the plasmodesmata. Some resistance occurs in the movement of water through symplast. It is a slightly slower process. |
Casparian strip is found in the endodermis. The walls of this layer are impervious to water because of the presence of suberin. So, it does not allow movement of water across the endodermis, rather is forced to enter the symplast pathway through cell membranes and reaches the xylem.