Water Potential Quiz

Water Potential Quiz Study Notes

Key Concepts

• Osmotic Potential

  • Describes the osmotic potential of the inside of a plant cell.

  • Depends on whether the solute dissociates in water and the impact these molecules have on osmotic potential.

  • Typically scales with about -0.1 MPa per 10 m of height.

  • Always positive, as adding solutes increases the activity of the solute.

Air Bubbles in the Xylem

• Prevention Mechanisms

  • Air bubbles in the xylem are prevented from moving through:

    • Callose deposition.

    • Redundancy of xylem vessels (plants have more than necessary).

    • Bordered pits that allow water, but not air, to move between xylem elements (e.g., vessels and tracheids).

    • Perforation plates at the end of xylem vessels serve a similar function but are less effective due to larger holes.

Components of Water Potential

• Positive Components

  • The component of water potential that is normally positive for the inside of a cell at the top of a tall tree, assuming the tree is well-watered:

    • Pressure potential

Turgid Cells

• Definition

  • A turgid cell is:

    • A cell with positive pressure (hydrostatic potential).

    • Opposite of a flaccid or plasmolysed cell (which has reduced turgor).

Stomata Opening Mechanisms

• Mechanisms for Opening of Stomata

  • Stomata open through several mechanisms, notably:

    • Gain of potassium by the guard cell leading to increased turgor.

    • Gain of potassium in the subsidiary cells may also contribute to stomatal opening.