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Why Is Blood Work Such An Amzing Things For Lehman College Ajhk

3591 words - 15 pages

SCI 114 – Scientific Principles of Forensic Science
Page 1
Laboratory Exercise: Presumptive Testing for Blood and Blood Typing
Name: ____________________________________________ Date: _____________________
Section #: ________
Background: Presumptive Testing for Blood and Blood Typing
Forensic evidence from crime scenes comes in many forms, and may contain biological
material that could link a suspect to the crime. Forensic Biology is a subset of forensic science
that deals with the characterization of biological materials such as blood, semen, saliva, and
skin cells from forensic evidence. Blood is a circulating tissue consisting of three types of cells:
red blood cells, white blood cells, and platelets1. These cells are suspended in a liquid known
as plasma (serum) and perform specific functions throughout the body1. For instance, red
blood cells (erythrocytes) carry respiratory gases, mainly oxygen and carbon dioxide to other
tissues in the body.
Suspected bloodstains at the crime scene are often identified by using a screening, or
presumptive, test. Presumptive tests for blood depend on the presence, and enzymatic
activity, of hemoglobin2. Hemoglobin, an iron-containing protein, is the component of red
blood cells, which is responsible for the transport of oxygen and the red color of blood. When a
colorless chemical reagent and hydrogen peroxide are added to a possible bloodstain, the
hemoglobin present in blood acts as a catalyst for the oxidation of the reagent to produce a
distinct color change. Kastle-Meyers reagent test, Leucomalachite Green reagent test, and
Luminol are presumptive tests that will indicate the possible presence of blood. Each reagent is
added to a suspected bloodstain, followed by the addition of hydrogen peroxide to result in a
specific color change (see Figure 1a-c). These screening tests for blood are very sensitive,
provide results quickly, and are relatively easy to perform at the scene of the crime.
Figure 13: (a) Kastle-Meyer’s Reagent Test produces a pink color in the presence of hemoglobin; (b) Leuco
Malachite Green Test produces a blue-green color in the presence of hemoglobin; (c) Luminol will generate a bluish
light in the presence of blood.
1
Source: Bertino, A., & Bertino, P. (2009). Forensic Science: Fundamentals & Investigations (p.197). Mason, Ohio: South-Western Cengage
Learning.
2
Source: Fisher, B. (2009). Introduction to Criminalistics (p. 243). Burlington, Massachusetts: Elsevier Inc.
3
Source: https://dps.mn.gov/divisions/bca/bca-divisions/forensic-science/Pages/forensic-programs-crime-scene-luminol.aspx
SCI 114 – Scientific Principles of Forensic Science
Laboratory Exercise: Presumptive Testing for Blood
Page 2
These chemical tests are termed presumptive, because a positive reaction (color change
or generation of light) would only be a tentative indication of blood, and a confirmatory test
must be conducted in order to determine if the sample is definitely blood4. When...

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