Water potential Knowledge-Based Practice

Questions

1. 1.

   Two adjacent plant cells, X and Y, are in direct osmotic contact. Cell X has a solute potential ($\Psi_s$) of $-0.8\text{ MPa}$ and a pressure potential ($\Psi_p$) of $+0.5\text{ MPa}$, whereas Cell Y has a solute potential ($\Psi_s$) of $-0.6\text{ MPa}$ and a pressure potential ($\Psi_p$) of $+0.1\text{ MPa}$. Which statement correctly predicts the direction of net water movement between these two cells?

   • A) Net movement will occur from Cell Y to Cell X because Cell X has a lower solute potential.
   • B) Net movement will occur from Cell Y to Cell X because Cell Y has a lower pressure potential.
   • C) Net movement will occur from Cell X to Cell Y because Cell X has a higher total water potential.
   • D) There will be no net movement of water because the solute and pressure components counterbalance each other.
2. 2.

   When a living plant cell reaches dynamic equilibrium after being placed in an open container of pure water, what relationship exists among its water potential components?

   • A) Its water potential becomes more negative than its solute potential because pressure potential becomes negative.
   • B) Its pressure potential decreases to zero, causing its total water potential to equal its solute potential.
   • C) Its solute potential increases to zero, while its pressure potential remains completely unchanged.
   • D) Its pressure potential increases until it is equal in magnitude and opposite in sign to its solute potential, resulting in a total water potential of zero.
3. 3.

   Which statement correctly describes the components of water potential in a plant cell at the point of incipient plasmolysis?

   • A) The pressure potential ($\Psi_p$) drops to 0 MPa, which makes the total water potential ($\Psi$) equal to the solute potential ($\Psi_s$).
   • B) The solute potential ($\Psi_s$) rises to 0 MPa, which makes the total water potential ($\Psi$) equal to the pressure potential ($\Psi_p$).
   • C) The pressure potential ($\Psi_p$) becomes highly negative, which makes the total water potential ($\Psi$) significantly lower than the solute potential ($\Psi_s$).
   • D) The total water potential ($\Psi$) reaches 0 MPa, because the positive pressure potential exactly cancels out the negative solute potential.
4. 4.

   How does the addition of solutes to an open container of pure water affect both its solute potential ($\Psi_s$) and its total water potential ($\Psi$)?

   • A) Solute potential increases above zero, which increases total water potential.
   • B) Solute potential decreases to a negative value, which lowers total water potential.
   • C) Solute potential remains unchanged at zero, but total water potential decreases.
   • D) Solute potential becomes negative, while total water potential remains constant due to atmospheric pressure.
5. 5.

   A plant cell with a solute potential ($\Psi_s$) of $-0.7\text{ MPa}$ and a pressure potential ($\Psi_p$) of $+0.2\text{ MPa}$ is placed in an open beaker of pure water ($\Psi = 0\text{ MPa}$). In which direction will water initially move, and what is the initial water potential of the cell?

   • A) Water moves out of the cell because the cell's initial water potential is $-0.9\text{ MPa}$.
   • B) Water moves out of the cell because the cell's initial water potential is $+0.5\text{ MPa}$.
   • C) Water moves into the cell because the cell's initial water potential is $-0.5\text{ MPa}$.
   • D) There is no net movement of water because the cell's initial water potential is $0\text{ MPa}$.

Answers and step-by-step solutions appear after you finish the test.