SolutionsSolutions Water is considered the solvent.Water is considered the solvent. The substance(s) dissolved in water is / The substance(s) dissolved in water is /

are the solute(s).are the solute(s). Together, solvent + solute Together, solvent + solute solution. solution. Concentration is the number of solutes Concentration is the number of solutes

in each volume of solventin each volume of solvent

OsmosisOsmosis

The diffusion of water across The diffusion of water across a semipermeable membrane a semipermeable membrane is called is called osmosisosmosis..

In a solution, there are water In a solution, there are water molecules and dissolved molecules and dissolved particles (the solute). particles (the solute).

The more dissolved particles The more dissolved particles there are, the lower the there are, the lower the concentration of water concentration of water molecules.molecules.

ANIMATION

Comparing SolutionsComparing Solutions

A solution may be desribed as A solution may be desribed as isotonicisotonic, , hypertonichypertonic or or hypotonichypotonic relative to relative to another solutionanother solution

These are comparisons; they require a These are comparisons; they require a point of reference (ie, my hair is shorter… point of reference (ie, my hair is shorter… …than it was last year). …than it was last year).

The comparison in biology is usually to the The comparison in biology is usually to the inside of a cell.inside of a cell.

IsotonicIsotonic A solution is A solution is isotonicisotonic to a to a

cell if it has the cell if it has the samesame concentration of dissolved concentration of dissolved particles as the cell. particles as the cell.

This means the water This means the water concentration is also the concentration is also the same. same.

Water molecules move into Water molecules move into and out of the cell at an and out of the cell at an equal rate in an isotonic equal rate in an isotonic solution.solution.

The cell size remains the The cell size remains the same.same.

HypertonicHypertonic

A A hypertonichypertonic solution has solution has a a higherhigher concentration of concentration of dissolved particles than a dissolved particles than a cell. cell.

This means the water This means the water concentration is lower than concentration is lower than that of the cell.that of the cell.

Thus, water flows out of Thus, water flows out of the cell – so, the cell will the cell – so, the cell will shrivel and eventually die.shrivel and eventually die.

ANIMATION

HypotonicHypotonic

A A hypotonichypotonic solution has a solution has a lowerlower concentration of concentration of dissolved particles than a dissolved particles than a cell. cell.

Therefore the water Therefore the water concentration is higher concentration is higher than that of the cell.than that of the cell.

Thus, water diffuses into Thus, water diffuses into the cell – causing the cell the cell – causing the cell to expand and potentially to expand and potentially burst.burst.

Impact on CellsImpact on Cells

In an In an isotonicisotonic solution (center), water enters / exits solution (center), water enters / exits red blood cells at equal rates.red blood cells at equal rates.

In a In a hypertonichypertonic solution (like salt water – right), solution (like salt water – right), water rushes out and the cell water rushes out and the cell shrivels.shrivels.

In a In a hypotonichypotonic solution (like distilled water – left), solution (like distilled water – left), water rushes in and the cell swells / bursts (water rushes in and the cell swells / bursts ( lysislysis).).

Video clips:

RBC in isotonic solution

RBC in hypertonic solution

RBC in hypotonic solution

Adaptations - PlantsAdaptations - Plants Plant cells use the cell wall to prevent bursting. Plant cells use the cell wall to prevent bursting.

At center, the plant cell is in an isotonic solution. Water moves in / out at equal rates (no NET movement)

At left, the plant cell is in a hypotonic solution.

Water rushes in, filling the vacuole.

This cell is turgid / has high turgor pressure.

At right, the plant cell is in a hypertonic solution.

Water rushes out of the cell, draining the vacuole.

This is called plasmolysis.Video: Elodea in isotonic / hyper / hypo

Adaptations - ProtistsAdaptations - Protists

Paramecia live in Paramecia live in freshwaterfreshwater

This makes paramecia This makes paramecia hypertonichypertonic to their to their surroundingssurroundings

Water is constantly Water is constantly rushing rushing intointo the the parameciumparamecium

So the paramecium uses So the paramecium uses a a contractile vacuolecontractile vacuole to to pump the water back out pump the water back out (and prevent bursting(and prevent bursting))

Video: The contractile vacuole in action