Find the correct expression for a fully turgid cell

Options

A. `Psi_(W)=Psi_(S)`
B. `Psi_(W)=0`
C. `Psi_(W)=Psi_(s)+Psi_(P)`
D. `Psi_(W)=Psi_(P)`

Answer

To find the correct expression for a fully turgid cell, we need to understand the concepts of water potential (Ψw), solute potential (Ψs), and pressure potential (Ψp).

### Step-by-Step Solution:

1. **Understanding Turgidity**: A turgid cell is one that is swollen and firm due to the uptake of water. This occurs when water enters the cell through osmosis, causing the vacuole to expand and push the cell membrane against the cell wall.

2. **Water Potential (Ψw)**: The water potential of a cell is the potential energy of water in that cell compared to pure water. It is influenced by both solute potential and pressure potential. The equation for water potential is:
\[ Ψw = Ψs + Ψp \]
where:
- Ψw = water potential
- Ψs = solute potential
- Ψp = pressure potential

3. **Conditions in a Fully Turgid Cell**:
- In a fully turgid cell, the cell is filled with water, and the pressure potential (Ψp) is at its maximum because the vacuole is pressing against the cell wall.
- The solute potential (Ψs) is typically negative due to the presence of solutes in the cell, but in a fully turgid state, the water potential (Ψw) approaches zero because the pressure potential counteracts the negative solute potential.

4. **Conclusion**: For a fully turgid cell, the water potential (Ψw) can be expressed as:
\[ Ψw = 0 \]
This indicates that the cell is in a state where there is no net movement of water in or out, as it is fully turgid.

5. **Final Expression**: Therefore, the correct expression for a fully turgid cell is:
\[ Ψw = Ψs + Ψp \quad \text{(where Ψw = 0)} \]