D 2.3 water potential

1. Why is water an excellent solvent?

Because it is polar — oxygen is partially negative, hydrogens partially positive.

2. What is solvation?

Water molecules surrounding solutes to dissolve them.

3. How does water dissolve ions?

Cations attracted to oxygen; anions attracted to hydrogen.

4. What are hydration shells?

Water molecules surrounding ions/polar molecules to prevent clumping.

5. What is osmosis?

Net movement of water from hypotonic → hypertonic solution.

6. Define hypotonic.

Lower solute concentration.

7. Define hypertonic.

Higher solute concentration.

8. Define isotonic.

Equal solute concentration; no net water movement.

9. What happens to cells in hypertonic solutions?

Water leaves → shrink.

10. What happens to cells in hypotonic solutions?

Water enters → swell.

11. What do aquaporins do?

Increase membrane permeability to water.

12. Can cells change osmosis direction?

No — only rate, by altering aquaporin expression.

13. What happens to animal cells in hypotonic solutions?

Water enters → lysis.

14. What happens to animal cells in hypertonic solutions?

Water leaves → crenation.

• Water leaves the cell by osmosis, causing the cell to shrink and wrinkle — a process called crenation.

15. What happens to plant cells in hypotonic solutions?

Water enters → turgid (healthy).

• Hypotonic surroundings have higher water potential, so water flows into the plant cell.

• The rigid cell wall prevents bursting, and the buildup of turgor pressure keeps the plant firm

16. What happens to plant cells in hypertonic solutions?

Water leaves → flaccid → plasmolysis.

• Hypertonic conditions pull water out of the cell.

• The cell loses turgor and becomes flaccid.

• If water loss continues, the membrane detaches from the cell wall → plasmolysis.

17. Why are isotonic solutions used medically?

Prevent cell swelling/shrinking.

18. Examples of isotonic uses?

IV fluids, wound rinsing, eye drops, organ preservation.

19. What is water potential (Ψ)?

Measure of free energy of water; water moves from higher → lower Ψ.

20. What is the water potential of pure water?

Ψ = 0 (reference value).

21. How do solutes affect Ψ?

Solutes decrease Ψ (make it more negative).

22. How does pressure affect Ψ?

Pressure increases Ψ (more positive).

23. Hypertonic solution effect on Ψ?

Lower Ψ outside → water leaves cell.

24. Hypotonic solution effect on Ψ?

Higher Ψ outside → water enters cell.

25. Isotonic solution effect on Ψ?

Equal Ψ → no net movement.

26. What happens when external Ψ > internal Ψ?

Water enters → turgor pressure builds → turgid.

• Higher external water potential means more free water outside, so water moves into the cell.

• This increases turgor pressure, which supports plant structure.

27. What happens when external Ψ < internal Ψ?

Water leaves → flaccid → plasmolysis.

• Lower external water potential means more solutes outside, so water moves out of the cell.

• The cell becomes flaccid, and severe water loss causes plasmolysis.

Solvation

Water surrounding solutes.

Hydration shell

Water encircling ions/polar molecules.

Lysis

Cell bursting.

Crenation:

Cell shrinking/wrinkling.

Turgor pressure:

Pressure of water pushing membrane against cell wall.

Flaccid

Condition when plant cells lose water and become limp.

Turgid

Condition of plant cell when full of water and pressurized, healthy state.

Plasmolysis

Separation of the plasma membrane from the cell wall due to severe water loss.