Activity 1.7 - Determining blood types

Learning aims:

Students are supposed to learn what the basis of blood types division is. They will also learn about the basic blood types.

Materials:

school set for determining blood type, a picture to explain the antigen – antibody bond, Internet connection, interactive board or computers for pairs of students, plastic tubes, stickers, marker, slides, measuring cup, teaspoon, distilled water, citric acid, washing soda (soda ash, Na2CO3), low-fat milk, calcium chloratum, starch

Suggestions for use:

The blood type determination and transfusions games, that students can find on Internet, enable them to play roles of medical staff and decide about patient‘s lives by determining their blood type and infusing them with the right blood type*.

While doing this they learn that on the surface of red blood cells there are antigens that react with antibodies in blood plasma of a different blood type.

Exercise 1

Student's task is to determine the blood type of unknown blood sample (imitation with the set for school). It is possible to get an educational set designed for this exercise, where students do not work with real blood, but with a model “blood” that works just like real one.

If there is no set available, you can use the following alternative model*:

Colour all “blood” samples with the red food dye or waterpaint.

Blood type A
Colour the low-fat milk.

Blood type B
Use syrup Calcium chloratum (available in a pharmacy).

Blood type AB
Carefully mix the low-fat milk and Calcium chloratum in the ratio 1:1

Blood type 0
Boil the distilled water and add a small amount of starch dissolved in water.

Reagent Anti-A
Dissolve 1 small teaspoon of citric acid in 40 ml of distilled water.

Reagent Anti-B
Dissolve 1 small teaspoon of washing soda in 40 ml of distilled water.

Procedure:

On the slide (better with two shallow holes) marked by the letters A and B add two drops of chosen samples (“blood type” unknown to pupils).
Add a drop of reagent anti-A to the drop of the sample marked with the letter A, and add a drop of reagent anti-B to the other drop of sample marked with the letter B.

In the real blood the antibody in the reagent anti-A reacts with antigens on the surface of red blood cells of blood types A and AB. The antibody in the reagent anti-B reacts with antigens on the surface of red blood cells of blood types B and AB.

The precipitation in our model occurs in 30 seconds in all cases.

Group A blood does not react with anti-B, group B blood does not react with anti-A, group 0 blood does not react with either anti-A or anti-B. In these cases, no coagulate is observed.

According to the reaction of the tested sample and reagent anti-A and anti-B (clot apperas in both or only in one or in none of two drops), blood type of “unknown” sample can be determined.

Important notes

  1. "Blood" can be stored in a refrigerator up to one day.
    2. Use distilled water for the preparation of reagents and blood type 0.
    3. Prepare 20 ml of each blood sample and 40 ml of each reagent (anti-A and anti-B).
    4. A drop of blood and a drop of reagent on the slide should be approximately of the same size.

Ask students to explain what they think happened during blood testing.

Why does blood coagulate somewhere but does not somewhere else? How does the test work?

Let them describe the situation in the pictures in their own words.

Students have to be able to explain that antigens and antibodies in blood are of two types: A and B. A type blood contains antigens A on the surface of red blood cells and antibodies B in plasma that do not react with each other. Red cells of B type blood carry antigens B and plasma contains antibodies A which react with antigens of group A. Therefore, blood of types A and B coagulates when the two are mixed. Blood cells of group AB do not contain any antibodies but in plasma both types of antigens are present. Blood cells of group 0 do not have antigens but in plasma there are both antibodies A and B. A different type of blood type is a rhesus factor which can be positive if its antigen is present or negative if the antigen is not present in blood.

It can encourage students to design "recipe" for a similar model. As the blood type B they can use, for example, a solution of baking soda (sodium bicarbonate) or an aqueous solution of egg white – (2 parts water and one part of the egg whites; allow the precipitate to settle; collect the clear solution for use). As the reagent in both cases, use 70 % ethanol (alcohol for disinfection, available in a pharmacy).

Exercise 2

Angela was told by her doctor that her newly born baby needs intensive care because he inherited rhesus positive factor from his father.

Look up in your textbook or on the Internet what rhesus factor is.

The doctor did not tell Angela why rhesus positive factor of her child is a problem. Can you explain it?

* © Katarína Kimáková for ESTABLISH

Students can find an interactive game for example on following web page: http://nobelprize.org/

Possible questions:
  • Do animals also have blood types like people?
  • I do not know my blood type. Where can I determine my blood type?