Describe: Osmosis.

(N/A) $ \Rightarrow $ Definition: Osmosis is the spontaneous net movement of solvent molecules (usually water) through a selectively permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides.
$ \Rightarrow $ Direction of movement: Water moves from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) across a semi-permeable membrane.
$ \Rightarrow $ Plant cell characteristics:
- Plant cells are surrounded by a cell membrane and a cell wall.
- The cell wall is freely permeable to water and substances in solution and is not a barrier to movement.
- In plant cells, the vacuole and its membrane, the tonoplast, along with the plasma membrane, are important determinants of the movement of molecules in or out of the cell.
$ \Rightarrow $ Key Principles:
- Osmosis occurs spontaneously in response to a driving force.
- The net direction and rate of osmosis depend on both the pressure gradient and the concentration gradient.
- Water moves from its region of higher chemical potential (higher concentration) to its region of lower chemical potential until equilibrium is reached.
- At equilibrium, the two chambers have the same water potential.
$ \Rightarrow $ Thistle Funnel Experiment:
- $ A $ thistle funnel is filled with a concentrated sucrose solution and its mouth is covered with a semi-permeable membrane (e.g., egg membrane).
- It is placed in a beaker containing pure water.
- Water enters the funnel due to osmosis, causing the level of the solution in the funnel to rise.
- This continues until equilibrium is reached.
$ \Rightarrow $ Osmotic Pressure:
- External pressure can be applied to the solution to prevent the entry of water through the semi-permeable membrane.
- The pressure required to completely stop the entry of water is called osmotic pressure.
- Numerically, osmotic pressure is equivalent to the osmotic potential, but with an opposite sign (osmotic pressure is positive, while osmotic potential is negative).