BIO 1007 Lab Checklists | BIO 1007 Resources | Mrs. Caley Opsal's Home | IVCC Home | Contact Us
Introduction:
In general, substances move across plasma membranes by two principle kinds of processes: passive and active. In passive or physical processes, substances move because of differences in concentration (or pressure) from regions of higher concentration (or pressure) to regions of lower concentration (or pressure). The movement usually continues until either an equilibrium or an even distribution of substances is accomplished. Passive processes are usually the result of the kinetic energy (energy of motion) of the substances themselves and the cell does not expend energy to move the substances. Examples of passive processes are diffusion, osmosis, filtration, and dialysis.
In active or physiological processes, substances may move from areas of lower to higher concentration. In addition, cells must expend energy to carry on active processes. Examples of active processes are active transport, phagocytosis, and pinocytosis.
DIFFUSION
Diffusion is the net (greater) movement of molecules or ions from a region of higher concentration to a region of lesser concentration until they are evenly distributed. An example of diffusion in the human body is the movement of oxygen and carbon dioxide between body cells and blood.
To demonstrate diffusion, using forceps, carefully place a large crystal of potassium permanganate into a test tube filled with water. Place the tube in a rack against a white background where it will not be disturbed. Watch the diffusion of the crystal through the water at 30-minute intervals for the entire laboratory period. The distance of diffusion can be measured and recorded in millimeters using a millimeter ruler.
Time Distance in mm
30 minutes ______________
60 minutes ______________
90 minutes ______________
120 minutes _____________
DIALYSIS
Dialysis is the separation of smaller molecules from larger ones by using a selectively permeable membrane that permits diffusion of the smaller molecules but not the larger. The principle of dialysis is used with artificial kidneys.
Place a prepared solution containing starch, sodium chloride, glucose, and albumin into a piece of dialysis tubing. Tie off the tubing with string and rinse the outside of the tubing thoroughly with distilled water.
Blot the tubing with paper towel and weigh to the nearest tenth of a gram:___________ g
Immerse the tubing in a beaker of distilled water.
After 1 hour, test the water in the beaker (this is called the dialysate) for the presence of each of the substances in the tubing as follows:
1. Albumin- add several drops of Biuret reagent to 2 ml of the dialysate in a test tube. If protein is present, Biuret will turn a purple color.
2. Glucose- test 5 ml of the dialysate in a test tube with 2-3 ml of Benedict's solution. Heat the test tube for about 3 minutes in a hot (near boiling) water bath. If glucose is present a colored precipitate (green---yellow---orange---red) will be formed.
3. Starch- add several drops of iodine (IKI or KI) solution to 2 ml of the dialysate in a test tube. Positive reaction = blue-black color.
4. Sodium chloride- Place 2 ml of dialysate in a test tube and add several drops of 1% silver nitrate. Positive reaction = white precipitate.
Blot the tubing again with paper towel and weigh to the nearest tenth of a gram.______ g
Questions:
1. Has the tubing gained or lost weight? Why?
2. What substances, if any, moved into the tubing?
3. What substances moved out of the tubing? Why?
4. What substances remained in the tubing and could not move out? Why?
Last Updated 05/26/06
BIO 1007 Lab Checklists | BIO 1007 Resources | Mrs. Caley Opsal's Home | IVCC Home | Contact Us