In a turgid cell, __________.

• A. Ψ_S is always positive
• B. Ψ_P is 0
• C. Ψ_P < 0
• D. Ψ = Ψ_S
• E. Ψ = 0

Answer: (E)

Verified step by step guidance

1. Understand the concept of water potential (Ψ) in plant cells, which is the sum of solute potential (ΨS) and pressure potential (ΨP). The formula is: <math xmlns='http://www.w3.org/1998/Math/MathML'><mi>Ψ</mi> = <msub><mi>Ψ</mi><mi>S</mi></msub> + <msub><mi>Ψ</mi><mi>P</mi></msub></math>.
2. Recognize that in a turgid cell, the cell is fully inflated with water, and the pressure potential (ΨP) is at its maximum because the cell wall is exerting pressure back on the cell contents.
3. Recall that in a turgid cell, the solute potential (ΨS) is negative because solutes lower the water potential, but the pressure potential (ΨP) is positive and equal in magnitude to the solute potential, making the overall water potential (Ψ) zero.
4. Analyze the given options: ΨS is always positive, ΨP is 0, and ΨP S. In a turgid cell, ΨS cannot be positive, and ΨP is not zero; instead, ΨP is positive and balances the negative ΨS.
5. Conclude that the correct condition for a turgid cell is when the overall water potential (Ψ) is zero, meaning the pressure potential (ΨP) exactly counteracts the solute potential (ΨS), resulting in <math xmlns='http://www.w3.org/1998/Math/MathML'><mi>Ψ</mi> = 0</math>.