Whose Blood is it?: Teacher's Notes
EQUIPMENT AND REAGENTS
- microscope slide
- tooth picks
- dropper bottles for simulated blood samples
- dropper bottles for simulated antiserums
- magnifying glass
- black paper mat
- safety glasses
- disposable gloves
- paper towels
Type O Blood - water and red food coloring
Type B Blood – 4% Polyvinyl Alcohol solution. Dissolve 10 grams of PVOH in about 200 mL of deionized water. Mix and heat gently until dissolved. Dilute to 250 mL. (PVOH can also be purchased from chemical supply house already dissolved and diluted to 4%.) Add red food coloring.
Type A Blood - 0.25M sodium carbonate. Dissolve 6.25 grams of Na2C03 in 250 ml of deionized water. Add red food coloring.
Anti-B Serum - 4% sodium borate. Dissolve 10 gms of Na2B407•10H20 in 250 ml of deionized water. (Household laundry borax can be used.) Add blue food coloring. (Solution may be saturated. Allow excess to settle.)
Anti-A Serum - 0.25M calcium chloride. Dissolve 6.9 grams of CaCL2 in 250 ml of deionized water. Add yellow food coloring.
This experiment should be presented at a level that is appropriate for your class. The hand-out, while simplifying the "science", may still be too detailed for younger students. The terms Anti-A and Anti-8 may need clarification. Perhaps destroys A or destroys B would illustrate the point better for some students. Anti-A antibodies will destroy Type A blood and a reaction will be noted. It will not destroy Type B or O blood. There will be no reaction.
It should be noted that since there are no real blood products used in this experiment, it cannot be used to do actual blood typing. This should be mentioned to the students in case anyone decides to type themselves or their lab partner. Students should be gloved for this experiment if possible to simulate the safety measures a real technician would have taken while working with blood.
The Anti-A reaction produces small crystals. The magnifying glass and black mat are not really needed, but add to the effect. The Anti-B reaction is a thickening of the drop to form a gel.
Fill the sample bottles according to the outcome you choose for the case, and the blood type you choose for the neighbor and the injured man. In one possibility, both the victim and car blood samples will test positive for the Anti-A test and negative to the Anti-B, and are thus Type A. The neighbor's blood, Type O, water and food coloring, will test negative for both. If every sample tests out as having the same blood type, a discussion on the problems the police will have in determining what happened can follow.
Paper towels will be needed to wipe off the microscope slide and the toothpicks used for mixing (if reusable plastic ones are used) after each sample is tested to prevent contamination of the samples.
Alternately, the circles on the data sheet could be colored black, avoiding the need for the black mat. If placed in plastic sheet protectors, or laminated, the tests can be done directly on the data sheet and the microscope slide is not needed either.
A discussion of reasons for observing safety precautions when handling blood samples could be held if desired, or alternately, a discussion of reasons why blood typing is important. Students could be asked if they know their own blood type. A survey of the classroom could be done to determine how classroom statistics on blood type distribution compare to the national averages.