Station 3.1 LAB
Thermal Systems in Health Fields
How the Body Regulates its Temperature
PRESENTATION AND PRACTICE
In this lab you will get to visualize the distribution of different temperatures across the surface of the hand. Then you will experiment with how exposure to hot and cold temperatures changes the way different temperatures are distributed. Finally, you will see how evaporation of water from the skin affects temperature.
The two experiments you will perform use sheets of liquid crystals. Have you ever heard the term LCD TV? LCD actually means liquid crystal display. Liquid crystals are molecules that change shape depending on the surrounding temperature. When the crystals change shape, the colors they reflect also change. There are different types of liquid crystals, and the sheets you will use have been designed to react differently at certain temperatures, called event temperatures.
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You will have 5 sheets each with a different event temperature: 28°C, 30°C, 32°C, 33°C, and 34°C. When you place the liquid crystal sheets on a warm object, you will see a mixture of brown/yellow, green and blue. Anything that is close to the event temperature of the sheet will appear green. Things that are lower than the event temperature will be brown/yellow, and things that are above the event temperature will be blue. |
Refer to this table for help remembering this:
Green |
|
Blue |
Nearly equal to event temperature |
Lower than event temperature |
Higher than event temperature |
*During both experiments, it is very important to make sure you do not get the liquid crystal sheets wet. Please take great care so that we can preserve the sheets for as long as possible. Paper towels will be provided just in case.
Also, when not using a liquid crystal sheet, please place the crystal surface down on the small pieces of paper provided to keep them clean.
Temperature Patterns
- Tell your coach that you are ready to begin the lab activity. He or she will then prepare a beaker of cold water in an ice bucket, and a beaker of warm water on a hot plate.
- You should have the five different liquid crystal sheets, each with strings that will allow them to be held tight to your hand. Start with the sheet with the lowest event temperature: 28°C. Place the black side that says 28°C down so that it is touching the back of your hand. Pull both strings so that the sheet is tight against your skin. Observe the color change.
- If the sheet turns solid blue, this means your hand is too warm to show any color differences at that event temperature. Remove the sheet and try the next event temperature. Continue moving up until you see a pattern that has a mixture of colors with a clear pattern.
- Write down the event temperature (in °C) of the clear sheet and use the colored pencils to draw the pattern you see on your answer sheet.
- Remove the sheet from your hand, and place it with the liquid crystal side down on its piece of paper to allow the sheet to reset.
- Starting with the same sheet that gave a distinct pattern on the back of your hand, place the sheet over the inside of your forearm, just under the elbow.
- Try different event temperatures until you see a mixture of colors like you did with the back of the hand. (If the sheet is mostly blue, you need to increase the event temperature; if the sheet is mostly brown/yellow, you need to decrease the event temperature.)
Write down the event temperature (in °C) that worked and use the colored pencils to draw the pattern you see on your answer sheet. - Remove the sheet from your forearm, and place it with the liquid crystal side down on its piece of paper to allow the sheet to reset.
- Finally, starting with the same sheet that worked for the back of the hand, place the sheet over the backside of your forearm, just under the elbow.
- Try different event temperatures until you see a mixture of colors like you did with the back of the hand. (If the sheet is mostly blue, you need to increase the event temperature; if the sheet is mostly brown/yellow, you need to decrease the event temperature.)
Write down the event temperature (in °C) that worked and use the colored pencils to draw the pattern you see on your answer sheet. - Remove the sheet from your forearm, and place it with the liquid crystal side down on its piece of paper.
- Now click on the following link, and use the “Convert Celsius to Fahrenheit” calculator to find the event temperatures you used in each part to °F, and record these on your answer sheet.
http://www.celsius-to-fahrenheit.com/ - Now read the following questions and write your answers on your answer sheet:
- What do you think caused the patterns of dark blue? (Think of a specific structure that is a major part of thermoregulation).
- Did you have to use a different event temperature for either side of your forearm than you did for the back of your hand? Why do you think this is?
Responses to Hot and Cold
- There should be a beaker of water being kept warm on a hot plate. Use a thermometer to find the temperature of the water in both °C and °F (a button on the thermometer allows you to switch between them). Record the temperatures you find on your answer sheet.
*Do not touch the tip of the thermometer to the bottom. You want to know the temperature of the water, not the glass. - There should also be a beaker of water being kept cold in an ice bucket. Again, use the thermometer to find the temperature of the water in both °C and °F. Record the temperatures on your answer sheet.
- Select the sheet that created a distinct pattern on the back of your hand in the first part of the experiment. Place the black side that says the temperature down so that it is touching the back of your hand. Pull both strings so that the sheet is tight against your skin.
- Make sure you see a similar pattern to what you observed in the first part, and record the event temperature of the liquid crystal sheet (in °C) on your answer sheet. Ask your coach to help you tie the sheet to your hand.
- Without getting the liquid crystals wet, place your fingertips in the beaker with the warm water for 1 minute. (You can use the provided stopwatch, your own watch, or a nearby clock to time it.) Observe the changes.
- Once the minute is up, pull your fingers out of the water and lay your hand flat on the table for another minute. Observe the changes.
- On your answer sheet, describe what happened while your fingers were in the warm water and what happened after removing them from the water.
- Now without getting the liquid crystals wet, place your fingertips in the beaker with the ice water for 1 minute. Observe the changes.
- Pull your fingers out of the water and lay your hand flat on the table for another minute. Observe the changes.
- Dry your hand and remove the liquid crystal sheet.
- On your answer sheet, describe what happened while your fingers were in the ice water and what happened after removing them from the water.
- Again, click on the following link and use the “Convert Celsius to Fahrenheit” calculator to find the event temperature you used to °F, and record it on your answer sheet. http://www.celsius-to-fahrenheit.com/
- Now read the following questions and write your answers on your answer sheet:
- What was happening in the body that caused the color change you saw while your fingertips were in the warm water? What does this have to do with thermoregulation?
- What was happening in the body that caused the color change you saw while your fingertips were in the cold water? What does this have to do with thermoregulation?
Evaporative Cooling
- Start with the liquid crystal sheet with the highest event temperature: 34°C. Place the black side that says 34°C down so that it is touching the back of your hand. Pull both strings so that the sheet is tight against your skin. Observe the color change.
- This time, we want the sheet to turn solid blue. If this doesn’t happen, remove the sheet and try the next event temperature. Keep moving down until you find the sheet that turns completely blue, and record that event temperature on your answer sheet.
- Remove the sheet from your hand.
- Dip the pointer finger of your other hand into the warm water from the last experiment, and pull it out to get a small drop. Touch the drop to the back of the hand where you will apply the liquid crystal sheet, and spread it around so it forms a thin layer about the size of a quarter in the center.
- Blow on the water until it dries completely. As soon as it has dried, replace the sheet that you chose in step 2 and pull it tight against your skin.
- QUICKLY use colored pencils to draw the pattern you see on your answer sheet.
- Once more, click on the following link and use the “Convert Celsius to Fahrenheit” calculator to find the event temperature you used to °F, and record it on your answer sheet. http://www.celsius-to-fahrenheit.com/
- Now read the following question and write your answer on your answer sheet:
- What happened to the temperature on the back of the hand after adding a drop of water and helping it to dry? What mechanism does the body use that takes advantage of this?
APPLICATION QUESTIONS – Write down your answers on your answer sheet
- Using what you learned from the differences in temperature on different parts of your arm, why do you think hibernating animals try to pack on lots of fat before winter?
- Using your observations from the heating and cooling experiment, what do you think contributes to the development of chilblains and frostbite, other than direct exposure to cold?
- Do you think sweating would be more effective at getting rid of excess heat for someone in the rainforest or someone in the desert? Why?
EVALUATION
Your lab performance will be evaluated by the criteria (standards) you will find in this project’s rubric. A rubric is simply a table that states how you will be evaluated. Your coach will use this table to report your performance.
CLICK HERE TO GO TO THE RUBRIC
LAB REVIEW
- Humans have the ability to maintain a constant healthy core temperature through thermoregulation.
- Animals that can use thermoregulation are called endotherms. Animals whose body temperatures depend on the environment are called ectotherms.
- The ideal core temperature for a human is 98.6°F (37°C), but the acceptable range is anywhere from 97.5 to 100°F.
- The control center for thermoregulation is in the hypothalamus of the brain, which attempts to maintain the core temperature at a specific value called the set point.
- Temperature is the average energy associated with how fast atoms or molecules are moving.
- Heat is the transfer of energy from something of high temperature to something of lower temperature.
- Heat loss can occur through conduction, convection or radiation.
- When the body reaches a temperature above the set point, the hypothalamus causes vasodilation and perspiration to accelerate heat loss.
- If the body’s mechanisms for getting rid of excess heat fail, a person may experience hyperthermia, heat exhaustion and eventually heat stroke.
- When the body reaches a temperature below the set point, the hypothalamus causes vasoconstriction, shivering thermogenesis, and hormonal thermogenesis.
- If the body’s mechanisms for conserving heat fail, a person may experience mild to profound hypothermia, chilblains and frostbite.
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Links to Station 3.1 Modules
Lab Intro | Lab Presentation and Practice | Communications Intro| Communications Presentation and Practice| Math