Question

Study the following table showing the components of water potential of four cells of an actively transpiring plant.
$\begin{array}{ccc}Cell& Solutepotential& Pressurepotential\\ & \left(MPa\right)& \left(MPa\right)\\ A& -0.68& 0.42\\ B& -0.75& 0.36\\ C& -0.83& 0.47\\ D& -0.57& 0.29\end{array}$
Identify the four cells as root hair, cortical cell, endodermal cell (lacking casparian strips) and pericycle cell respectively in the young root (assuming symplastic water flow through them).

• A. B, D, C, A
• B. D, A, C, B
• C. A, D, C, B
• D. A, C, B, D

Answer 1

The correct option is C

A, D, C, B

The movement of water from one cell to another cell through the plasmodesmata is called the symplast pathway. It occurs in the following sequence:
Root hair $\to$ Epidermis $\to$ Cortex $\to$ Endodermis $\to$ Pericycle $\to$ Xylem
Solute potential $\left({\psi }_s\right)$ and pressure potential $\left({\psi }_p\right)$ are two components of water potential. Water potential can be calculated using the formula:
$({\psi }_w={\psi }_s+{\psi }_p)$
Water always flows from higher potential to lower potential. The water potential values of the four given cells are:
A $\to$ - 0.68 + 0.42 = - 0.26
B $\to$ -0.75 + 0.36= - 0.39
C $\to$ - 0.83 + 0.47 = - 0.36
D $\to$ - 0.57 + 0.29 = - 0.28
So, the correct sequence of the flow of water is A $\to$ D $\to$ C $\to$ B.
Thus, A, D, C and B respectively are the root hair, cortical cell, endodermal cell and pericycle cell.