Lab #3: Diffusion and Osmosis

Solvent

dissolving agent

Solutes

dissolved substances

Selectively permeable

allowing water to freely pass through but regulating the movement of solutes

Diffusion

a physical process in which molecules move from an area where they are in high concentration to one where their concentration is lower.

Where does the energy for diffusion come from?

Comes from intrinsic kinetic energy (energy of motion) in all atoms and molecules. If nothing hinders the movement, a solute will diffuse until it reaches equilibrium.

Osmosis

The diffusion of water through a selectively permeable membrane from a region of higher to lower water concentration.

Brownian motion

Intrinsic kinetic energy of water molecules that causes larger particles, such as carmine, to diffuse down its gradient.

Is the movement of a single carmine particle random or directional?

Random, but collectively, they move downwards due to pressure underneath coverslip.

Does the movement ever stop?

No, KE of water hitting dye particles as well.

Do smaller particles move more rapidly than larger particles? Other observations?

Yes, smaller molecules move faster because smaller molecules have greater individual SA and experience more collisions/contact with H2O.

Are you actually observing molecular movement?

No, as water has KE, not particles. Random movement is KE, directional is due to pressure differences.

How can molecular movement bring about diffusion?

Solute particles (carmine) collide, generating more KE in region with higher concentration. Water will move from higher to lower energy, carrying carmine with it.

List several processes in cell metabolism where diffusion is important.

- Generation of proton-motive force in ETC.

- Acquisition of CO2 and O2.

What is dialysis tubing?

regenerated cellulose fibers formed into a flat tube.

What permeability was tested with dialysis tubing?

starch, reducing sugar (glucose), iodine potassium iodide (I2KI).

How was this experiment performed?

Dialysis tubing was filled with a solution of glucose and starch, which was then inserted into a solution of I2KI.

I2KI test for presence of starch

When I2KI is added to the unknown solution, the solution turns purple or black if starch is present. If no starch is present, the solution remains a pale yellow-amber color.

Benedict's test for reducing sugar

When Benedict's reagent is added to the unknown solution and the solution is heated, the solution turns green, orange or orange-red if a reducing sugar is present (the color indicates the sugar concentration). If no reducing sugar is present, the solution remains the color of Benedict's reagent.

What is significance of the final colors after the Benedict's tests? Did the results support your hypothesis?

Varying concentrations of sugar are present; higher sugar concentration=green, medium=orange, none=light blue.

Predict the size of the I2KI molecules based on your results (relative to glucose and starch).

glucose