Question

What would be the ${\Psi }_P$ of a flaccid cell? Which organisms other than plants possess cell wall ?

Answer 1

Flaccid cell :
Whenever a cell is present in an isotonic solution (when the osmotic pressure of the cytoplasm of the cell is in equilibrium with the external solution), the net flow of water is zero from inside to outside of a cell or vice versa. A state of equilibrium is achieved which leads to flaccidity.

Pressure potential:
The pressure potential ${\Psi }_P$ (also known as turgor potential which is directly proportional to potential energy of the system) of flaccid cell is $0$.

Cell wall:
Cell wall is a protective structure/ layer found outside the plasma membrane of plants and certain other organisms. It provides protection against mechanical stress.

Occurrence
Other than plants, bacteria, fungi and some protists also possess cell wall. However, the composition differs from one type of organism to the other.