OSMOSIS & TONICITY

SEC 4.3 PG 74-75

OSMOSIS: - a special case of diffusion involving water

- water molecules move across a selectively permeable membrane from an area of high water concentration to an area of low water concentration

- does not require ATP energy.

- Special channe; proteins allow water to pass through the cell membrane.

OSMOSIS • Movement of water across a membranes results in:• OSMOTIC PRESSURE:buildup of pressure due to osmosis.

• osmotic pressure acts against HYDROSTATIC PRESSURE to cause changes in osmotic apparatus (thistle tube, u-tube) and in cells.

• HYDROSTATIC PRESSURE: the pressure of gravity on the solution

TONICITY

• Tonicity refers to the strength of solution in relationship to osmosis.

• 3 terms to know:1. Isotonic2. Hypotonic3. Hypertonic

The type of solution will determine the movement of water!

ISOTONIC SOLUTIONS

• iso = “the same” • tonic = “solution”

• concentration of solute outside cell is the same as the solute concentration in the cell

• water moves into cell at equal rate to water moving out

• cell stays the same, is at EQUILIBRIUM

HYPOTONIC SOLUTIONS• hypo = “lower”

• solute concentration OUTSIDE cell = LOWER

• More water outside cell water moves INTO cell

• cell swells

• LYSIS –bursting may occur in animal cells

• TURGOR PRESSURE builds up in plant cells

Vacuole pushes outwards against cell wall

HYPERTONIC SOLUTIONS• hyper= “ higher”

• solute concentration outside cell is higher

• water concentration is lower outside cell

• net movement of water OUT OF cell

• CRENATION occurs in animal cells

• PLASMOLYSIS occurs in plant cells

D) E) F)

A) B) C)