Transport in Plants

Presence of Casparian strips in plants controls the amount of water and solute it absorbs. Thus, a plant that cannot produce Casparian strips effectively will be unable to control the amount of water and solute in plants.

The water potential is the chemical potential of the water, which is equivalent to diffusion pressure deficit with negative sign. Therefore, water potential $\left(\Psi_A\right)$ of cell A is

$\begin{gathered} \Psi_A=\Psi_S+\Psi_P=-20+5=-15 \text { bars } \\ \Psi_B=\Psi_S+\Psi_P=-18+2=-2 \text { bars } \end{gathered}$

Since, water moves from higher water potential to lower potential, the flow of water will be from cell B ($-$2 bars) to cell A ($-$15 bars).

In apoplast pathway, water passes from root hairs to xylem through cell wall only without crossing any membranes. The apoplast involves a continuous system of cell walls and intercellular air spaces in plant tissues.