BiomedicalSciencesExperimental Design



STEPHEN LAKES 1.1.5: Time of Death Experimental Introduction—highlight key info belowThe emergency call came in at 9:45 am. The police and the EMT arrived at the scene at 9:56 am. Anna Garcia, a 38 year old woman, was found dead lying face down in her entry hallway in a pool of blood. It was a comfortable 73?F inside Anna’s house despite it being 92?F outside. She was last seen alive the night before by her former husband Alex Garcia. Investigators are trying to piece together what happened between the time that she was last seen alive and when she was found dead at the scene. Clues hidden within the body will enable medical examiners to estimate her time of death. These signs include rigor mortis (the stiffening of the muscles that occurs shortly after death), lividity (the pooling of blood), algor mortis (the cooling of the body), clouding of the corneas, evidence of decomposition, and/or drying of the tissues.After death, a body will lose heat at a rate approximately one-and-a-half degrees per hour until it reaches the temperature of the surrounding environment. Many factors influence the rate of heat loss including clothing, victim size, and environmental factors such as temperature and humidity. The body core temperature can be measured rectally or with a hypodermic probe of the liver or brain, because of their large mass and density. In this activity you will investigate how ambient temperature, the temperature in a room or the temperature surrounding an object, affects the cooling rate of a simulated body. You will also estimate Anna’s time of death based on her core body temperature.1. Identify the Problem or QuestionState the research problem or question in one sentence.The problem should be very specific and measurable.Write one sentence in the form of a question or problem statement. See below, PLTW has written the problem statement/question for you. Feel free to delete the notes above about how to write a problem statement (and this comment).Problem Statement: How do different ambient temperatures affect the rate of body cooling?2. Predict a solution to the problem or an answer to the question. This will be in the form of a hypothesis.This solution design or hypothesis should be based on previously obtained knowledge or research and should be supported by scientific evidence.Write a one or two sentence statement predicting the outcome of the experiment. In other words, state IN A COMPLETE SENTENCE whether body temperature will change the quickest in hot weather, temperate weather or cold weather. Check your answer against at LEAST 2 other people to see if you agree (it’s ok if you don’t, but someone else might convince you to change your prediction). After you’ve done this, you may delete the instructions above if you’d like.Hypothesis: I Think that Cold climate will affect the bodies temp faster.Identify the independent and dependent variables.The independent variable is the variable that is varied or manipulated by the researcher. The dependent variable is the measurable effect, outcome, or response in which the researcher is interested. In other words, the independent variable is the presumed cause, whereas the dependent variable is the presumed effect. In an experiment, the independent variable is the variable that is controlled and manipulated by the experimenter; the dependent variable is not manipulated but instead is observed or measured for variations. Think you know the answer? Check your answer against at LEAST 2 other people to see if you agree (NOT MRS. HISRICH). After you’ve described the independent and dependent variable, you may delete these instructions.The independent variable is: ClimateThe dependent variable is: Ana’s Body3. Design the experiment to be used to test your hypothesis.Include a list of all materials used.Be specific.Take all safety concerns into account.Identify a control to be used for comparison if applicable.Control all outside variables that could affect the outcome of the experiment.Clearly define how the data will be collected and recorded, including measurement units.Design a data table to use to record information.Plan the strategy that will be used to summarize the data. For example, a graph might be used to summarize the data.Write a series of numbered steps and include a list of required materials. The data table should include units that will be used to collect data. You don’t have to do this, but these directions show you HOW it’s done. Clearly they’ve already done it for you (below). Feel free to delete these instructions once you’ve read them. Materials:3 Computers with Logger Pro software (you’ll just need one computer per person)3 Vernier Temperature Probes (you’ll just need one)Goggles (put on safety glasses IF you don’t already wear glasses)Gloves (don’t worry about these)Laboratory apron (don’t worry about these)Oven mitt (“hot” teams only)3 Ring stands with clamp (you’ll just need one)3 Test tubes (you’ll just need one)Sodium polyacrylate (also known as waterlock)—you’ll use Ghost Crystals insteadWeigh boats—(you’ll just need one)Electronic balance—there’s one on each side of the roomThermometer37?C Water—it’s in the water bath on the front tableGraduated cylinderHot water bath set to approximately 50?C—hot water groups will use the hot plate to prepare thisIce water bath—only for “cold” groupsRoom temperature water—only for “room temp” groups, get from sink and add warmer water if necessary to get it to about 20?CProcedure:Decide who will be the LEAD direction giver and make sure your team follows these steps. The other person/people will do most of the set-up & running of lab.Wear the appropriate personal protective equipment.Create the following three water baths: Just make the ONE that you were assigned!A 250 mL beaker filled with 200 mL of water on a hot plate set to medium heat that is approximately 50?C. On our hot plates, I’d turn it to high until it gets to 50?C and then turn it down until you find a number that maintains that temperature. This is TRICKY! You’ll probably need to fiddle with the dial throughout the lab.A 250 mL beaker filled with 200 mL of water at room temperature (approximately 20?C). Measure the temp to figure out what ACTUAL room temp is right now and adjust by adding warmer/cooler water as necessary.A 250 mL beaker filled with 200 mL ice water (0?C). Measure the temp to figure out what the EXACT temperature is (and record it).Obtain three test tubes and measure and place 1 gram of sodium polyacrylate into each. Just do one. You’ll use the ghost crystals by one of the scales. Turn on the scale and make sure it reads 0.000 g. Set the weigh boat on the tray and press the on/tare button to zero it SO IT WILL NOT WEIGH THE WEIGH BOAT. Add ghost crystals until it reads 1.000 g (0.8-1.2 g is ok).Obtain three Vernier Temperature Probes, three analog thermometers, and three ring stands with clamps. Just do one.Start Logger Pro? software on the computers. Just do one.Click on File Open and open the Forensics with Vernier folder. Open the program titled 14 Hot Air, Cold Body.Connect the LabQuest Mini to each computer using USB cables. Just do one.Connect the Temperature Probes (just do one) into CH 1 of the LabQuest Minis using the British Telecom connector.Place the thermometer in the water baths (just do one) to ensure that they maintain the correct temperatures. Record this temperature in the Evidence Record table.Attach the Temperature Probes (just do one) to the clamp on the ring stands. Place 20 mL of 37? water into the test tubes (just do one). These represent dead bodies. Use your GRADUATED CYLINDER to measure the 20 ml and use the water from the hot water bath on my desk. Bring your test tube WITH YOU. You can simply dip the G.C. into the water bath to get the 20 mL. Make sure to then pour it IMMEDIATELY into the test tube, combining the ghost crystals with the water to make your WATERLOCK. Set-up for COLDSet-up for ROOM TEMPSet-up for HOTPlace a test tube with waterlock representing the dead body in each of the three water baths. (just do the one you prepped in the bath that you prepped)Place a Temperature Probe in the center of each test tube with waterlock. (just do one)Click to begin data collection. Note that the experiment is set to collect data for 20 minutes. You’ll want to set it up/prop it so that you don’t have to hold it the whole time.Make sure to maintain a constant temperature for your water baths throughout data collection. When data collection is complete (data has been collected for 20 minutes OR temperature stops fluctuating), click the Statistics button, , to display a Statistics box.Record the minimum temperature recorded and the maximum temperature recorded in the appropriate spot in the Evidence Record table for each water bath. You’ll just do this step for YOUR OWN DATA.Record the temperature change and record in the Evidence Record table for each water bath. (Note: The temperature change is displayed in the Statistics box as Δy.) Walk around and visit other teams to collect their data. Copy the graphs by placing the mouse cursor over the graph, left clicking, and then pressing both the Control and the C keys simultaneously. Paste the graphs into a Word document and save (paste YOUR ONE GRAPH into THIS document under the header GRAPHS—everyone in your TEAM needs the graph, so you’ll also post it to the Moodle forum so your teammates can pull the graph. Here’s a link to the forum: ). To paste the graph, press both the Control and the V keys simultaneously. Repeat this step in order to copy and paste the Data Table into the Word document (That’s the data table from Vernier). Attach the graphs/tables in the Results section below.Repeat the experiment for a total of three trials. Please do TWO trials per team.Carry out the experiment.Collect data. Make plete multiple trials. (Perform the procedure many times, collecting data each time.)Complete the data table. Include units and labels for each section. Feel free to delete the directions above after reading them.Team Evidence RecordYOUR assigned temperature:(50?C, room temp or 0?C?)Actual Temperature of Water Bath (?C):Maximum Temperature of Waterlock (?C):Minimum Temperature of Waterlock (?C):Temperature Change (?C): 5051583820Class Results:Temp:Group 1 Temp Change (?C):Group 2 Temp Change (?C):Average Temp Change(?C):50?C9.92015Room temperature106.38.15 (0?C)292426.5Visit the other groups and collect their data for the table above. Include your own as well.Analyze the data and observations. Make graphs or charts of the data.Check that the independent and dependent variables are properly placed on any graphs.Be logical and clear. Look beyond the obvious.Make graphs and charts to visually and logically present the data. Write in paragraph form and include calculations showing all work. All analysis should be explained clearly and concisely. This is where you can put the graph/table you were to copy/paste in step 21. Feel free to delete the directions above after reading them. If you didn’t collect the data on YOUR laptop, you’ll need to pull the graph from the forum, where your teammate posted it: Graph:State the conclusion.Use a one sentence statement. Be clear and concise.Write a one sentence statement directly related to the original hypothesis. It might start with “The hypothesis was correct…” It might also say, the hypothesis was wrong… You should say what ACTUALLY HAPPENED (the REAL answer to the experimental question). Feel free to delete the directions above after reading them.Conclusion: My hypothesis was correct because Ana’s Body temp changed more in cold.Summary Paragraph: In this lab we tested the many different variables in climate that can change the body. I found out that cold temperature change the body the most. Hot stays pretty consistant but makes the body change slightly more than room temp. Room temperature changes the least.Conclusion—TYPE your answer in complete sentences (being thorough and specific)The Glaister equation is just one formula used to approximate the postmortem interval (Google the equation to learn more about it). If Anna had died outside instead of inside her air conditioned house, would the Glaister equation be an appropriate model to use to determine her time of death? (Remember that they were in the middle of a heat wave and it was 92?F outside.) Why or why not?Finished? Woo hoo! Upload your final lab report to the 1.1.5. upload link under the 1.1. folder in Moodle: . Please DO NOT PRINT this entire report. You may delete this message after reading it.Ana’s Body was dead at 7:00 A:M ................
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