D2.3 Water Potential Flashcards
Solvation
the interaction of a solvent with dissolved molecules or ions
Osmosis
The net movement of water molecules from a less concentration solution to a region of more concentration solution, across a partially permeable membrane
Hypertonic
when the external solution is more concentrated than the cell cytoplasm and there is a net outflow of water outside of the cell by osmosis
pressure potential increases as more water molecules enter the cell - increased pressure potential means there is more potential for water molecules to exert pressure against the membrane
solute concentration increases because no of solute molecules in comparison to water increase.
Hypotonic
when the external solution is less concentrated than the cell cytoplasm and there is a net inflow of water into the cell by osmosis
pressure potential decreases as water moves out from cell - decreased pressure potential means it’s more unliked for remaining water cells to put pressure on the membrane.
solute concentration decreases because the no of solute molecules relative to water molecules decreases
Isotonic
when the external solution is the same concentration as the cell cytoplasm and there is no net entry or exit of water from the cell by osmosis. (dynamic equilibrium)
Osmotic concentration
the measure of solute concentration, defined as the number of osmoles (Osm) of solute per (L).
Animal Cell
absence of cell wall
- in hypotonic solution will quickly swell and break open (lyse)
- in hypertonic solution shrink in size (crenated) = makes it harder for them to move smoothly through the capillaries, causing blood clots
Plant Cell
has cell wall
- in hypotonic solution will swell and become firm due to turgor pressure (turgid) = structural support prevents it from bursting
- in hypertonic solution it loses turgor and becomes flaccid and is said to become plasmolysed.
Turgor Pressure
Hydrostatic pressure in a cell that pushes the plasma membrane against the cell wall.
Plasmolysis
Condition when plant cell is in a hypertonic solution. When the cell membrane pulls away from the cell wall due to reduced cell volume and pressure.
Movement of plasma membrane away from the cell wall allows solute to enter the space between the wall and the membrane, causing damage to the membrane over time.
Osmosis in unicellular aquatic animals
Most organisms live in freshwater aquatic environment which are hypotonic environments
Adaptation = contractile vacuole
Contractile vacuole - works continuously to pump out excess water
Protist quickly bursts without it.
Water potential
the potential energy of water per unit volume relative to pure water, expressed in units of pressure (kPa)
High water potential = low solute concentration
Low water potential - high solute concentration
formula
water potential = solute potential + pressure potential
hydration shell
- positively chagred ions attracted to oxygen in water
- negatively charged ions attracted to hydrogen in water
- water molecules form hydration shells around many types of ions and charged molecules to prevent them from joining back together
osmotically active
solutes such as sodium, potassium, and chloride ions and glucose are said to be osmotically active because they dissolve in water and change the concentration of the solution.
