Question

In a fully turgid cell
A. ${\psi }_s$ is negative and ${\psi }_p$ is positive
B. ${\psi }_p$ is negative and ${\psi }_s$ is positive
C. Both ${\psi }_p$ and ${\psi }_s$ are positive
D. Both ${\psi }_s$ and ${\psi }_s$ are negative

Answer 1

Hint: Turgor pressure is the force within the cell that pushes the cell membrane against the cell wall. It is also defined as the pressure measured by a fluid called hydrostatic pressure and , measured at a particular point within itself when at equilibrium.

Complete answer:
Water potential is calculated by the sum of solute potential and pressure potential. The Solute potential is negative and pressure potential is positive. In a fully turgid cell, the solute potential is equal to pressure potential and consequently water potential is zero. Therefore, no water can go within a fully turgid cell.

${\psi }_w$= ${\psi }_s+{\psi }_p$ = 0
Here, ${\psi }_w$= water potential
${\psi }_s$= solute potential
${\psi }_p$= pressure potential

Additional Information: Significance of turgidity in plants are –
(1) It provides stability to a cell.
(2) Turgidity keeps the cell and its organelles fully distended, which is important for plants to live and grow normally.
(3) Turgor pressure helps in cell enlargement, consequently in stretching of the stems and keeping leaves erect and fully expanded.
(4) The turgid cells give mechanical support essential for the non-woody tissues.
(5) Loss of turgidity results in wilting of leaves and drooping of shoots.
(6) The opening and shutting of the stomata are regulated by the turgidity of the guard cells.
(7) Leaf movements of many plants are controlled by loss and gain of cell turgor.
(8) Due to turgor pressure, plumule and radicle force out from seeds at the time of seed germination.

So, the correct answers are, ‘${\psi }_s$ is negative and ${\psi }_p$ is positive’.

Note: Turgor pressure is actually pressure potential ${\psi }_p$. The pressure potential during a plant cell is typically positive. Solute potential ${\psi }_s$, also called osmotic potential, is negative in a plant cell and zero in distilled water.