Blood January 6, 2015

What is blood made of? erythrocytes Red blood cells (erythrocytes) Contain hemoglobin Transport O 2 White blood cells (leukocytes) Immune system Produce antibodies, attack and digest pathogens Platelets Essential to the repair of injured blood vessels and the formation of clots

What is blood made of? Plasma Plasma (liquid portion of blood)  Mostly water  metabolites  metabolites (molecules formed by chemical processes in the body) - example: sugars, amino acids)  Waste (example: urea)  ions Plasma makes up about 55% of whole blood

What is blood made of? Work with a partner to identify all the letters. Be prepared to justify your response! A B C D

Identifying Blood Stains … first, a definition presumptive test A presumptive test is a test that lets you know that a certain substance (i.e. blood) may be present. A negative result = NO blood present A positive result = blood may be present, or a different substance may be causing the positive result If investigators get a positive result with a presumptive test, they will usually pretty confident that blood is present – but they will need to do more tests to prove it in court. Nearly any test has some chance of providing the wrong result. Medical tests are often discussed in terms of rates of false positives and false negatives. AT-HOME PREGNANCY TEST very low rate of false positive a positive result means you are almost certainly pregnant high rate of false negative if you get a negative result you should retest in a few days. A MAMMOGRAM low rate of false negative Abnormal breast tissue is easily identified high rate of false positives only some abnormalities are cancerous. Do presumptive tests have high false negatives? Or high false positives?

Identifying blood stains Catalytic Color Tests The hemoglobin in blood acts like a catalyst for some oxidation reactions. Many different versions of this test, but all involve adding a chemical to a suspected blood stain. If blood is present, then it will catalyze a reaction, resulting in a color change. Catalyst – speeds up chemical reactions without being used up itself Oxidation – loss of electrons (e.g rusting of metal)

Identifying blood stains Catalytic Color Tests Causes of misleading results False negatives: a stain that has been cleaned with bleach will often not react False positives: some vegetables, including potatoes and horseradish Are catalytic color tests presumptive? Why or why not?

Identifying blood stains Luminol Uses chemiluminescence – the emission of light from a chemical reaction – to identify blood Sprayed over an area with suspected stains; blood will light up; investigators will photograph Very sensitive – can detect blood that has been washed away / diluted to 1 part per 5,000,000

Identifying blood stains Luminol Very sensitive, so few false negatives False positives: bleach, metals, plaster Is luminol a presumptive test? Why or why not?

Identifying blood stains Crystal tests Formation of crystals from the heme groups of hemoglobin Confirmatory test – very low incidence of false positives Does cause some false negatives – can be a difficult procedure to master Will do on Thursday! If a crystal test is confirmatory, why not just do that immediately?

Closure What was our objectives, and what did we learn? What was our learner profile trait and how did we demonstrate it? How does what we did today tie to our unit question?

Exit Ticket 1.Name the four components of blood. 2.All blood identification tests detect which component of blood? 3.Describe two tests for blood identification and explain whether or not each is presumptive or confirmatory.