Blood evidence is a crucial part of forensic science that... Show more
Health & Medicine249 views·Updated May 9, 2026·2 pagesDetailed Notes on Blood Evidence for PLTW Biomedical Science
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Kay@kay_pvji
1
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Blood Composition and Evidence Testing
Ever wonder what makes blood so useful for solving crimes? Human blood contains several key components that forensic scientists analyze. Erythrocytes (red blood cells) transport oxygen and contain hemoglobin, which gives blood its red color. Leukocytes (white blood cells) fight infection and are part of the immune system. Thrombocytes (platelets) help with blood clotting, and plasma carries nutrients, hormones, and waste products.
When investigators find potential blood at a crime scene, they first perform presumptive testing. Tests like Kastle-Meyer (using phenolphthalein) react with hemoglobin to suggest if a sample is blood. This is followed by confirmatory testing to verify it's actually blood by examining other properties like antigens.
Blood typing uses the ABO system to classify blood into four types (A, B, AB, and O) based on the antigens present on red blood cells. Each blood type also has specific antibodies—proteins that interact with antigens. When antibodies encounter the wrong type of antigen, they cause agglutination (clumping), which is how blood typing tests work.
Fascinating Fact: Red blood cells only live for about 120 days before being recycled by your liver and spleen. Your body constantly produces new ones to replace them!
Blood evidence can narrow down suspects by matching blood types, though common types like type A (found in 42% of the population) may not be conclusive on their own. In a crime scene investigation, blood evidence must be considered alongside other evidence like fingerprints, hair samples, and potential motives.
2
of 2
Blood Spatter Analysis
Blood doesn't just tell us who was at a crime scene—it can reveal what happened there! Blood spatter patterns come in different forms that tell different stories. Transfer patterns occur when bloody objects touch surfaces and can indicate if someone was dragged or crawled. Splatters happen when blood travels through the air before landing.
The shape of blood droplets tells us a lot about how they were created. Falling droplets that hit surfaces at 90° form circular patterns. When droplets hit at an angle, they create elliptical patterns with "tails" pointing in the direction of travel. The more elongated the droplet, the faster it was moving. Radial spatter occurs when a powerful impact sends blood droplets flying outward at high speed.
Forensic scientists can determine the height blood fell from by measuring the diameter of blood splatters. They create reference charts by dropping blood from different heights and measuring the resulting patterns. This analysis helps determine if a victim was standing, falling, or already on the ground when injured.
Crime Scene Insight: The angle and pattern of blood spatter can reveal whether a person was hit while standing or falling, helping investigators reconstruct the sequence of events during a crime.
In a typical blood spatter experiment, scientists drop blood from various heights onto paper and measure the diameter of each splatter. By comparing crime scene blood splatters to these reference measurements, they can estimate how high the blood source was when the drops formed. This evidence helps piece together what really happened during a violent incident.
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Health & Medicine249 views·Updated May 9, 2026·2 pagesDetailed Notes on Blood Evidence for PLTW Biomedical Science
K
Kay@kay_pvji
Blood evidence is a crucial part of forensic science that helps investigators solve crimes. By examining blood samples and patterns, forensic scientists can determine what happened at a crime scene and potentially identify suspects. This introduction to blood evidence covers... Show more
1
of 2Sign up to see the content. It's free!
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Blood Composition and Evidence Testing
Ever wonder what makes blood so useful for solving crimes? Human blood contains several key components that forensic scientists analyze. Erythrocytes (red blood cells) transport oxygen and contain hemoglobin, which gives blood its red color. Leukocytes (white blood cells) fight infection and are part of the immune system. Thrombocytes (platelets) help with blood clotting, and plasma carries nutrients, hormones, and waste products.
When investigators find potential blood at a crime scene, they first perform presumptive testing. Tests like Kastle-Meyer (using phenolphthalein) react with hemoglobin to suggest if a sample is blood. This is followed by confirmatory testing to verify it's actually blood by examining other properties like antigens.
Blood typing uses the ABO system to classify blood into four types (A, B, AB, and O) based on the antigens present on red blood cells. Each blood type also has specific antibodies—proteins that interact with antigens. When antibodies encounter the wrong type of antigen, they cause agglutination (clumping), which is how blood typing tests work.
Fascinating Fact: Red blood cells only live for about 120 days before being recycled by your liver and spleen. Your body constantly produces new ones to replace them!
Blood evidence can narrow down suspects by matching blood types, though common types like type A (found in 42% of the population) may not be conclusive on their own. In a crime scene investigation, blood evidence must be considered alongside other evidence like fingerprints, hair samples, and potential motives.
2
of 2Sign up to see the content. It's free!
- Access to all documents
- Improve your grades
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Blood Spatter Analysis
Blood doesn't just tell us who was at a crime scene—it can reveal what happened there! Blood spatter patterns come in different forms that tell different stories. Transfer patterns occur when bloody objects touch surfaces and can indicate if someone was dragged or crawled. Splatters happen when blood travels through the air before landing.
The shape of blood droplets tells us a lot about how they were created. Falling droplets that hit surfaces at 90° form circular patterns. When droplets hit at an angle, they create elliptical patterns with "tails" pointing in the direction of travel. The more elongated the droplet, the faster it was moving. Radial spatter occurs when a powerful impact sends blood droplets flying outward at high speed.
Forensic scientists can determine the height blood fell from by measuring the diameter of blood splatters. They create reference charts by dropping blood from different heights and measuring the resulting patterns. This analysis helps determine if a victim was standing, falling, or already on the ground when injured.
Crime Scene Insight: The angle and pattern of blood spatter can reveal whether a person was hit while standing or falling, helping investigators reconstruct the sequence of events during a crime.
In a typical blood spatter experiment, scientists drop blood from various heights onto paper and measure the diameter of each splatter. By comparing crime scene blood splatters to these reference measurements, they can estimate how high the blood source was when the drops formed. This evidence helps piece together what really happened during a violent incident.
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI companion is specifically built for the needs of students. Based on the millions of content pieces we have on the platform we can provide truly meaningful and relevant answers to students. But its not only about answers, the companion is even more about guiding students through their daily learning challenges, with personalised study plans, quizzes or content pieces in the chat and 100% personalisation based on the students skills and developments.
Where can I download the Knowunity app?
You can download the app in the Google Play Store and in the Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
Similar Content
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Analyze the initial social and religious encounters between Europeans, Africans, and Indigenous peoples in the colonial Americas.
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Analyze the political and cultural transitions from the Roman Empire to the Byzantine Empire, focusing on the reign of Justinian I and his code.
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Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.6/5App Store
4.7/5Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan SiOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha KlichAndroid user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
AnnaiOS user