Diffusion and Osmosis

Diffusion is the movement of molecules from a high concentration to a low concentration. Many molecules diffuse across cell membranes.

Concentration Gradient Both water and solutes (substances dissolved in water) Diffuse down their Concentration Gradients.

Dynamic Equilibrium Diffusion is the result of the random motion of atoms/molecules. It tends to distribute substances uniformly throughout a solution. This uniform/even distribution is called Dynamic Equilibrium. The atoms/molecules still continue to move but the distribution remains uniform throughout the solution.

Osmosis Osmosis is the diffusion of a solvent (water) across a selectively permeable membrane.

Cell Membrane The cell membrane forms the outer boundary of the cell. It determines what enters and leaves the cell.

Osmotic Concentration Concentrations of all solutes determine what is called the Osmotic Concentration. Osmotic concentrations can be broken down into 3 categories. Hypertonic, Isotonic, and Hypotonic

Hypertonic solutions Hypertonic solutions: (hyper = more than) In the case of cells, the solution outside the cell is more concentrated with a solute than the solution inside of the cell. Example: Blood cells in saltwater.

Isotonic solutions Isotonic solutions: (iso = the same) In the case of cells, the solutions inside and outside of the cells contain an equal amount of solutes.

Hypotonic solutions Hypotonic solutions: (hypo = less than) In the case of cells, the solution inside the cell contains more solutes than the solution outside the cell. Example: Red blood cells in pure water.

Plant Cells and Osmosis In addition to a cell membrane, plant cells are surrounded by a rigid cell wall. The cell wall provides structure for plants like bones do for animals. Plant cells shrink and expand in different osmotic solutions, but are confined by their cell walls.