Fig. 1 shows the results of a blood-group test carried out before a hospital patient receives surgery. The patient's blood cells were mixed separately with ...
Question 1 Report
Fig. 1 shows the results of a blood-group test carried out before a hospital patient receives surgery. The patient's blood cells were mixed separately with anti-A serum and anti-B serum. Clumping, called agglutination, shows that the matching antigen is present on the surface of the red blood cells. Blood group is determined by inherited alleles and is an example of variation in humans. The hospital also recorded the patient's body mass, but body mass is not used to choose compatible donor blood. A nurse must identify the group correctly before blood is given.
(a) Which blood-group antigen is present on the patient's red blood cells? [1]
(b) Name the patient's ABO blood group. [1]
(c) What type of variation is ABO blood group? [1]
(d) Describe why ABO blood group is discontinuous variation. [2]
(e) Suggest why a patient with this blood group should not receive blood containing A antigens. [2]
(f) Use the information to state one reason body mass is not a suitable characteristic for assigning a blood group. [1]
(g) Describe one precaution a nurse should take to avoid a testing error. [2]
Answer Details
(a) Clumping occurs with anti-B serum, so B antigen is present on the red blood cells [1].
(b) Cells with B antigen but no A antigen are blood group B [1].
(c) ABO blood group is discontinuous variation [1].
(d) There are distinct blood-group categories [1], A, B, AB and O, with no intermediate groups between them [1].
(e) A person with group B may have anti-A antibodies in their plasma [1]. These antibodies would cause donor red cells carrying A antigens to agglutinate or be destroyed [1].
(f) Body mass is unsuitable because it has a continuous range and is not determined by ABO alleles [1].
(g) Use labelled, clean equipment and prevent samples mixing [1], and repeat the test or test a known control sample [1]. These precautions reduce contamination and help identify an incorrect result.
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