Diffusion Principles

Cell Membranes and Diffusion In order to function, cells are required to move materials in and out of their cytoplasm via their cell membranes. These membranes are semipermeable, meaning that certain molecules are allowed to pass through, but not others. This movement of molecules is mediated by the phospholipid bilayer and its embedded proteins, some of which act as transport channels for molecules that otherwise would not be able to pass through the membrane, such as ions and carbohydrates.

Diffusion in Agar ExpandNOTE: In this exercise, you will be given agar containing an indicator chemical called phenolphthalein. When phenolphthalein is exposed to the normal alkaline conditions in the agar, it will look pink. But when it is exposed to neutral or acidic conditions, it changes from pink to clear. You will make different size and shaped agar cubes as a model for cells to study the impact of cell size and shape on diffusion rate. To make the first set of cells, measure out and cut...

Preparation of Solutions for the Agar Cube Experiment ExpandIMPORTANT: Wear gloves, goggles, and appropriate personal protective equipment – chemicals can be hazardous at high concentrations. For the diffusion indicator solution, weigh out 1 g of phenolphthalein and add it to a beaker containing 100 mL of 95% ethanol. To make the basic solution for the agar, measure 80 mL of water into a beaker, and then add 0.4 g of NaOH. Stir until the solute is dissolved then bring the total volume of the...

Source: Laboratory of Dr. Lynne O'Connell — Boston College When the conditions of a system at equilibrium are altered, the system responds in such a way as to maintain the equilibrium. In 1888, Henri-Lewis Le Châtelier described this phenomenon in a principle that states, "When a change in temperature, pressure, or concentration disturbs a system in chemical equilibrium, the change will be counteracted by an alteration in the equilibrium composition." This experiment demonstrates Le Châtelier's...

Werner Heisenberg considered the limits of how accurately one can measure properties of an electron or other microscopic particles. He determined that there is a fundamental limit to how accurately one can measure both a particle’s position and its momentum simultaneously. The more accurate the measurement of the momentum of a particle is known, the less accurate the position at that time is known and vice versa. This is what is now called the Heisenberg uncertainty principle. He mathematically...