Biology OSMOSIS

### KEY TOPICS

star Osmosis
star Questions regarding Osmosis
star Experiment

### OSMOSIS

● 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.")

### QUESTIONS REGARDING OSMOSIS

● 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)?

### EXPERIMENT

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.