● The `color{violet}("plant cell")` is surrounded by a `color{brown}("cell membrane")` and a `color{brown}("cell wall.")`

● The cell wall is `color{brown}("freely permeable")` to water and substances in solution hence is not a barrier to movement.

● In `color{violet}("plants the cells")` usually contain a large `color{brown}("central vacuole")`, whose contents, the `color{brown}("vacuolar sap")`, contribute to the `color{brown}("solute potential")` of the cell.

● In `color{violet}("plant cells,")` the cell membrane and the membrane of the vacuole, the `color{brown}("tonoplast")` together are important determinants of `color{violet}("movement of molecules")` in or out of the cell.


● `color{brown}("Osmosis")` is the term used to refer specifically to the `color{violet}("diffusion of water")` across a differentially- or `color{brown}("semi-permeable membrane.")`

● `color{violet}("Osmosis")` occurs spontaneously in response to a `color{brown}("driving force.")`

● The net direction and rate of osmosis depends on both the `color{brown}("pressure gradient")` and `color{brown}("concentration gradient.")`

● Water will move from its region of `color{brown}("higher chemical potential")` (or concentration) to its region of lower chemical potential until equilibrium is reached.

● At equilibrium the two chambers should have the `color{violet}("same water potential.")`

● Study the Figure in which the two chambers, A and B, containing solutions are separated by a semi-permeable membrane.

(a) Solution of which chamber has a `color{violet}("lower water potential?")`

(b) Solution of which chamber has a `color{violet}("lower solute potential?")`


(c) In which direction will `color{violet}("osmosis occur?")`

(d) Which solution has a `color{violet}("higher solute potential?")`

(e) At equilibrium which chamber will have `color{violet}("lower water potential?")`

(f) If one chamber has a `color{brown}(Psi)` of `color{violet}("– 2000 kPa")`, and the other `color{violet}("– 1000 kPa")`, which is the chamber that has the higher `color{brown}(Psi)`?

`color{green}(star \ \ "Making a Semipermeable Membrane:")`


● One can get this kind of a membrane in an egg.

● Remove the yolk and albumin through a small hole at one end of the egg, and place the `color{brown}("shell")`
in dilute solution of `color{brown}("hydrochloric acid")` for a few hours.

● The `color{violet}("egg shell ")` dissolves leaving the membrane intact.

`color{green}(star \ \ "Experiment:")`

● A `color{brown}("solution of sucrose")` in water taken in a funnel is separated from `color{violet}("pure water ")` in a beaker through
a `color{violet}("semi-permeable membrane")`

● Water will move into the funnel, resulting in rise in the level of the solution in the funnel.

● This will continue till the `color{brown}("equilibrium")` is reached.

● `color{violet}("External pressure")` can be applied from the upper part of the `color{violet}("funnel")` such that no water diffuses into the `color{violet}("funnel through the membrane.")`

● This pressure required to prevent water from diffusing is in fact, the `color{violet}("osmotic pressure")` and this is the function of the solute concentration; more the solute concentration, greater will be the pressure required to prevent water from diffusing in.

● Numerically `color{brown}("osmotic pressure")` is equivalent to the `color{brown}("osmotic potential,")` but the sign is opposite.

● `color{violet}("Osmotic pressure")` is the positive pressure applied, while `color{violet}("osmotic potential ")` is negative.