Step 4. Osmosis Lab, steps 11-12
Channel: Bad Idea
Date: 2021-01-30

Osmosis is the process by which water is transported into and out of the cells. Osmosis is the spontaneous net movement of water through a partially permeable membrane to an area with higher solute concentration without the input of any energy.
Free water is not bound to the molecules of solute and therefore has free energy and free water molecules that are ready to diffuse. When water molecules are bound to solute molecules, it is much harder for them to move across a semipermeable membrane. The movement of water depends on molarity of a solution on the other side of the semipermeable membrane and not on the size of molecules. Net movement of water across the semipermeable membrane stops when the concentration of solute is equal on both sides of the membrane, and therefore equilibrium is reached.
Depending on the concentration of solutes, the relationship of two different solutions can be expressed as isotonic, hypertonic and hypotonic. Two solutions are isotonic to each other when their concentrations are the same. No net movement of water will occur between these solutions in case if they are separated by the semipermeable membrane.
The solution that is more concentrated compared to another is called hypertonic. The solution that is less concentrated compared to another is called hypotonic. The net movement of water will occur from the hypotonic solution towards the hypertonic solution.
In most organisms, cells live in an isotonic extracellular environment and therefore are able to keep their normal shape and function properly. Animal cells will swell when they are placed in a hypotonic solution. Some cells, such as erythrocytes, will actually burst as water enters them by osmosis. Placing animal cells in a hypertonic solution causes them to shrink as water leaves them by osmosis. It is important that animal cells be maintained in an isotonic medium, which has a solute concentration close to that of the cell cytosol.