Chapter 5-5.5- Osmosis Flashcards
What is osmosis?
Osmosis is a particular type of diffusion- specially the diffusion of water across a partially permeable membrane.
As with all types of diffusion it is a passive process and energy is not required.
What is water potential?
A solute is a substance dissolved in a solvent (for example water) forming a solution.
The amount of solute in a certain volume of aqueous solution is the concentration. Water potential is the pressure exerted by water molecules as they collide with a membrane or container. It is measured in units of pressure Pascals (Pa) or kilopascals (kPa). The symbol for water potential is the Greek letter psi.
Pure water is defined as having a water potential of 0kPa (at standard temperature and atmospheric pressure- 25(*C) and 100KPa.
This is the highest possible value for water potential, as the presence of a solute in water lowers the water potential below zero. All solutions have negative water potentials- the more concentrated the solution the more negative the water potential.
When solutions of different concentrations, and therefore different water potentials, are separated by a partially permeable membrane, the water molecules can move between the solutions but the solutes usually cannot.
There will be a net movement of water from the solution with the higher water potential (less concentrated) to the solution with the lower water potential (more concentrated). This will continue until the water potential is equal on both sides of the membrane (equilibrium).
