Question

What would be \[{{\text{ }\!\!\psi\!\!\text{ }}_{\text{p}}}\] of a flaccid cell? Which organisms other than plants possess cell walls?

Answer 1

Hint: Water potential and pressure potential within a flaccid cell is equal, hence turgor pressure is zero.

Complete Answer:
- Water potential (\[{{\text{ }\!\!\psi\!\!\text{ }}_{\text{w}}}\]) is a basic principle for understanding movement of the water. The two key components that determine water potential are the solute potential (\[{{\text{ }\!\!\psi\!\!\text{ }}_{\text{s}}}\]) and the pressure potential (\[{{\text{ }\!\!\psi\!\!\text{ }}_{\text{p}}}\]).By convention, at normal temperatures, the water potential of pure water, which is not under any pressure, is taken as zero.

- The pressure exerted by the protoplasts on the rigid walls due to the entry of water is known as pressure potential \[{{\text{ }\!\!\psi\!\!\text{ }}_{\text{p}}}\].
- If a pressure above atmospheric pressure is applied to pure water or a solution it increases its water potential. When water enters a plant cell due to diffusion, pressure against the cell wall can build up, making the cell turgid.
- This results in an increase in pressure potential. Pressure potential is generally positive, though negative potential or strain in the water column in the xylem plays an important role in transporting water up a stem in plants.

- A cell is said to be flaccid when water flows in and out of the cell and is in equilibrium. There is no pressure exerted by the protoplast against the cell wall. The pressure potential thus would be zero.
- A cell wall is the semi-permeable membrane surrounding a cell's cell membrane and providing structural support. It also functions to allow materials to enter and exit within the cell. In addition to plants, fungi, bacteria, archaea, and algae also have cell walls.

Note: Turgor pressure plays a key role in the growth of plant cells where the cell wall is expanded irreversibly due to the force of turgor pressure as well as structural changes in the cell wall which alter its flexibility.