FRQ OSMOSIS LAB

What is osmosis?

The diffusion of water across a selectively permeable membrane from high water potential to low water potential.

What does isotonic mean?

Equal solute concentration inside and outside the cell → no net water movement → cell stays the same.

What does hypertonic mean?

More solute and less water outside the cell → water moves out → cell shrinks.

What does hypotonic mean?

Less solute and more water outside the cell → water moves in → cell swells.

What is water potential (Ψ)?

A measure of free energy of water; water moves from high Ψ to low Ψ.

Formula for water potential (Ψ)?

Ψ = Ψs + Ψp (solute potential + pressure potential).

Formula for solute potential (Ψs)?

Ψs = –iCRT.

In Ψs = –iCRT, what does each variable mean?

i = ionization constant, C = molarity, R = pressure constant (0.0831), T = temperature in Kelvin.

What is the independent variable in the osmosis potato lab?

The sucrose solution concentration.

What is the dependent variable in the osmosis potato lab?

The percent change in mass of the potato cores.

What does the isotonic point on the graph tell you?

The molarity where % change in mass = 0 → solute concentration of the potato cells.

Why does a potato in salt water lose mass?

The solution is hypertonic, so water leaves the potato by osmosis.