D2.3 Water Potential PPT

Factors Affecting Water Movement into/Out of Cells

• Water movement in and out of cells is influenced by:

  • Solute concentration

  • Pressure potential

  • Semi-permeable nature of cell membranes

Comparison of Plant and Animal Cell Regulation

• Animal Cells:

  • Use contractile vacuoles for osmoregulation in freshwater environments.

  • Cells can undergo cytolysis (swelling and bursting in hypotonic solutions) and crenation (shrinking in hypertonic solutions).

• Plant Cells:

  • Have rigid cell walls that prevent bursting under turgor pressure conditions in hypotonic solutions.

  • Can experience plasmolysis in hypertonic environments (cell shrinkage from cell wall).

Solvation with Water as the Solvent (D2.3.1)

• Water molecule interactions:

  • Formation of hydrogen bonds due to electric attraction between attracted H and O.

  • Weak intermolecular bonds compared to covalent bonds.

• Process of solvation involves:

  • Dissolving solute in water:

    • Solute: present in smaller amounts (e.g., NaCl).

    • Solvent: largest amount (usually water).

  • Example: NaCl(s) dissolves into Na+(aq) and Cl-(aq).

Water and Solvent Properties (D2.3.1)

• Water as a versatile solvent:

  • Aqueous solutions: water acts as the solvent.

  • Ionic compounds dissolve easily in water due to polar nature, forming hydration shells.

  • Cations attracted to partially negative oxygen, anions to partially positive hydrogen.

  • Covalent compounds dissolve via hydrogen bonds.

Osmosis (D2.3.2)

• Definition and Mechanism:

  • Osmosis is diffusion of water from areas of high water concentration to low across a semi-permeable membrane.

  • Triggers turgor pressure maintenance and cell regulation.

• Definitions of Solutions:

  • Hypertonic: more solute, less water.

  • Hypotonic: less solute, more water.

  • Isotonic: equal solute and water concentrations.

Osmolarity Comparisons (Pages 9-10)

• Osmolarity defined as total concentration of solutes:

  • Low osmolarity: fewer solute particles per liter.

  • High osmolarity: more solute particles per liter.

  • Movement of water from low to high osmolarity solutions when separated by a permeable membrane.

Tonicity and Cell Behavior (Page 11-12)

• Tonicity considers:

  • Relative solute concentration and permeability.

• Directions of water movement:

  • Hypertonic solutions cause water to move out of cells (shrink).

  • Hypotonic solutions cause water to move into cells (swell).

Effects of Tonicity on Animal Cells (Page 17)

• Cytolysis: occurs when cells burst in hypotonic solutions.

• Crenation: occurs when cells shrivel in hypertonic solutions.

Plant Cell Water Regulation (Pages 24-27)

• Plant cells maintain turgor pressure in hypotonic solutions:

  • Pressure from cell wall prevents bursting.

  • Plasmolysis occurs in hypertonic solutions creating limp cells.

Experimental Observations (Page 28-30)

• Changes due to water movement:

  • Measure changes in mass and length under hypotonic and hypertonic solutions.

Water Potential (D2.3.8)

• Definition:

  • Water moves from higher to lower potential, depends on pressure and solute concentration.

• Water potential calculations:

  • Ψ = Ψs + Ψp

  • Ψs: solute potential (osmotic pressure), typically negative.

  • Ψp: pressure potential, can be positive or negative.

Movement of Water (D2.3.9)

• Direction determined by:

  • Net movement due to differences in solute concentration and water potential.

Osmosis in Practical Applications (Page 20)

• Kidneys regulate blood osmolarity, prompting water movement:

  • Antidiuretic hormone (ADH) influences urine concentration and water retention.

Applications of Isotonic Solutions (D2.3.7)

• Used in medical settings for:

  • Intravenous therapy (rehydration), wound rinsing, maintaining moisture in grafts, and organ transportation.

Conclusion

• Understanding water potential is crucial for:

  • Predicting water movement in and out of cells.

  • Relating water behavior to solute concentration and pressure influences.