D2.3 - Water Potential

Define solvation

The interaction of a solvent with the molecules and ions that dissolve in it (solute)

Explain how water dissolves solutes

The polar molecules orient themselves around the solute, forming hydrogen bonds with the positive and negative charges of the solute

Define osmosis

Diffusion of H2O from areas of lower concentration to higher concentration through a selectively permeable membrane

Distinguish hypertonic, hypotonic, and isotonic solutions in the context of cells

Hypertonic: Higher solute concentration outside of the cell; to maintain homeostasis, solvent (usually water) rushes out, causing the cell to shrivel up/shrink

Hypotonic: Higher solute concentration in the cell; to maintain homeostasis, solvent (usually water) rushes inside the cell, causing it to swell.

Isotonic: Zero net inflow of solvent due to equal solute concentrations inside and outside the cell. Solvent is always diffusing through the membrane, however—it’s just diffusing in and out at equal rates.

Define dynamic equilibrium

Solvent (water) continuously diffuses across the membrane, but no net inflow/outflow

Describe osmosis in cells without a cell wall

Hypotonic solutions can cause the cell to burst due to an excessive amount of water.

Hypertonic solutions cause the cell to shrivel up, eventually resulting in them becoming crenated.

Describe osmosis in plant cells (with a cell wall)

Hypotonic solutions cause the inflow of water, which flows to the permanent vacuole; this swells, placing pressure on the cytoplasm and cell wall.

Hypertonic solutions cause the volume of the permanent vacuole and cytoplasm to decrease. This results in the cytoplasm pulling away from the cell wall (cell becomes flaccid/plasmolysed)

Define the contractile vacuole

An organelle found in amoebas (unicellular organisms) that live in freshwater. Its job is to pump out the constant inflow of water

Define turgor pressure

Pressure caused by the stretching of a cell wall; eventually ends water intake