Water potential is less than ‘zero’ when

Options

A. Cell is flaccid
B. Cell is plasmolysed
C. Cell is partly turgid
D. All the above

Answer

To determine when water potential is less than zero, we need to understand the concept of water potential and how it is influenced by solute concentration and pressure. Here's a step-by-step solution:

### Step 1: Understand Water Potential
Water potential (Ψ) is a measure of the potential energy of water in a system. It is influenced by two main factors: solute potential (Ψs) and pressure potential (Ψp). The formula for water potential is:
\[ Ψ = Ψs + Ψp \]

### Step 2: Identify the Water Potential of Pure Water
At standard conditions (normal temperature and pressure), the water potential of pure water is defined as zero (Ψ = 0). This serves as a reference point.

### Step 3: Analyze the Effect of Solute Concentration
When solutes are added to water, the solute potential (Ψs) becomes negative. The presence of solute particles reduces the free energy of the water, leading to a decrease in water potential. The more solute particles present, the more negative the solute potential.

### Step 4: Consider Different Cell States
1. **Flaccid Cells**: In flaccid cells, there is a loss of turgor pressure, and the water potential is typically less than zero due to the presence of solutes.
2. **Plasmolyzed Cells**: In plasmolyzed cells, the cell membrane pulls away from the cell wall due to water loss, indicating a very low water potential, often negative.
3. **Partly Turgid Cells**: Even in cells that are partly turgid, the presence of solutes means that the water potential can still be less than zero.

### Step 5: Conclusion
Since in all these states (flaccid, plasmolyzed, and partly turgid), the water potential is influenced by solute concentration and is typically less than zero, we conclude that the correct answer is that water potential is less than zero in all of these cases.

### Final Answer
Water potential is less than zero when the cell is flaccid, plasmolyzed, or partly turgid. Therefore, the correct answer is **all of the above**.

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