During today's Bio lesson, we carried out 3 blood tests on 6 samples to determine which was a blood sample. As Ms Tan revealed, the blood sample was from cockles and blood sample 6 was actually watermelon juice (no wonder it looked so familiar). The 3 blood tests were examples of blood tests forensic scientists would carry out on samples from crime scenes. However, more specific tests, such as a DNA test and Spectrophotometric test, could be carried out to determine if the blood is human blood.
Test 1 Results:
Samples tested +ve for catalase: 4, 5 and 6
Test 2 Results:
Samples that glow in the luminol test: 4 and 5
Samples that glow in the luminol test: 4 and 5Test 3 results:
Observation: Only 4 turned an intense pink.
Conclusion of all 3 tests: Sample 4 contains blood and hence, is the real blood sample from the crime scene.
Questions
1. Why is it necessary to use more than one test to determine whether the given stain is blood?
It is because more than one chemical might react to the same test and yield positive results. Hence, more than one test is needed to eliminate uncertainties and other factors to achieve more conclusive results.
2. Once you know that a stain is real blood, what else would you do as a forensic scientist?
DNA analysis of the blood sample.
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