d2.3 water potiential

What types of interactions occur between water molecules and solutes during solvation?

Water forms hydrogen bonds with polar molecules and ion-dipole interactions with ions. The partial charges on the water molecule attract both cations and anions, stabilizing them in solution.

Describe the direction of water movement between two solutions of differing solute concentration, using correct terminology.

Water moves by osmosis from the hypotonic solution (lower solute concentration) to the hypertonic solution (higher solute concentration) to reach equilibrium. This is driven by the difference in water potential, not water concentration.

What happens to the net water movement in an isotonic solution and why?

In an isotonic environment, the solute concentration is equal inside and outside the cell. Water molecules continue to move in both directions, but net movement is zero due to dynamic equilibrium.

How can the isotonic point of plant tissue be experimentally determined?

By immersing identical tissue samples in solutions of varying solute concentrations and measuring changes in mass or length. The isotonic point is the concentration where no net gain or loss is observed. Graphing results with standard deviation/error bars enhances reliability.

What cellular consequences occur for animal cells in hypotonic and hypertonic environments?

In hypotonic solutions, water influx causes cells to swell and possibly lyse. In hypertonic solutions, water efflux leads to cell shrinkage and crenation. Unicellular organisms use contractile vacuoles to expel excess water; multicellular animals require isotonic fluids to avoid damage.

How do plant cells respond to hypotonic and hypertonic environments?

In hypotonic solutions, plant cells become turgid due to increased turgor pressure. In hypertonic environments, they lose water, the plasma membrane retracts from the cell wall, and plasmolysis occurs.

Why are isotonic solutions critical in medical practice?

Isotonic solutions prevent osmotic imbalances during treatments like IV therapy or organ preservation by maintaining the shape and function of cells in contact with the fluid, preventing lysis or shrinkage.

What is water potential and how is it measured?

Water potential (ψ) is the potential energy of water per unit volume relative to pure water at atmospheric pressure and 20°C. It’s measured in kilopascals (kPa), with pure water defined as 0 kPa.

Why does water move from regions of higher to lower water potential?

Water moves down its potential energy gradient to reach a lower-energy, more stable state, allowing systems to move toward equilibrium. Solute addition and pressure changes alter this gradient.

How do solute and pressure potentials combine to determine total water potential in plant cells?

Using the equation ψw = ψs + ψp, where:

• ψs (solute potential) is negative (due to dissolved solutes)

• ψp (pressure potential) is usually positive in turgid cells
  The sum determines the direction of water movement.

How does water potential explain the changes in plant tissue immersed in hypotonic vs hypertonic solutions?

In hypotonic environments, low external solute potential drives water into cells (ψoutside > ψinside), increasing pressure potential and turgidity. In hypertonic solutions, water leaves cells (ψoutside < ψinside), decreasing pressure potential and causing plasmolysis.

What variables influence the direction of water movement in plant and animal tissues?

Solute concentration, pressure potential, membrane permeability, and structural differences (e.g., cell wall presence) all determine water movement via osmosis and water potential gradients.

What are the biological implications of solubility differences among substances?

Solubility determines how molecules are transported, stored, or excreted. Hydrophilic substances dissolve in aqueous environments; hydrophobic ones require carriers. This affects nutrition, signaling, waste removal, and cell structure.