Energy Loss: Estimating The Percentage Of Energy Lost.

Energy Loss: estimating the percentage of energy lost.

Introduction: There’s no such thing as a free lunch; every organism on the planet must get its energy from something else. Autotrophs (such as plants, algae and cyanobacteria) get their energy from the sun. Herbivores, such as cows, get their energy from eating autotrophs, carnivores get their energy from eating herbivores (or other carnivores) and detritivores get their energy from anything that has died. Ultimately, however, all of an organism’s energy comes from the sun (either directly or indirectly). As energy is passed up a food chain, much of it is lost. Just as an engine loses some of its energy as heat, living organisms also radiate much of their consumed energy in the form of heat. That heat is the result of food being used to power an organism continually; its metabolism. In addition, not all food is digested. Thus, not all of the energy that is eaten by an individual may be passed onto the thing that eats it. Energy is often measured in calories. A calorie is the amount of energy required to heat 1 mL of water by 1 degree Celsius. A food Calorie (what you would find on your nutrition label) is actually 1000 calories (or 1 kilocalorie). In other words, if you could get all of the 140 Calories out of a can of Coca-Cola, it would be enough energy to heat 1400 mL of water from 0º C to boiling!

Title: Estimating the percentage of consumed energy lost as body heat.

Fundamental Question: How much of the energy put into our bodies (through eating, drinking) is lost as heat?

Testable Question: Since we are not manipulating a variable in this lab, you do not need a testable question.

Background: Write a background in your lab notebook that addresses the following components (from the CHS lab checklist):

 Discusses why the fundamental question is important; its biological significance or relevance. Why would it be important to be able to calculate the amount of energy lost?  Explains and discusses the concepts learned in class as they relate to the problem being investigated (conservation of energy, 90%/10% rules, energy transfer through a food chain, energy pyramids, etc…)  Explains how those concepts relate to their experimental design and procedures (why are you doing what you’re doing? Why heat water? Keep an accurate food log?)  Outside sources cited in MLA format.

Hypothesis: Since we are not manipulating a variable in this lab, you do not need to write a hypothesis in the standard “If…, then… because…” format. Predict the percentage of your food’s energy that will be lost as heat and provide the reasoning behind your prediction.

Instructions: Create a protocol of the experiment as described below. Refer to the CHS lab checklist (e.g. don’t forget materials and amounts).

Day One: 1. Create a table (AKA a “food log”) that you can carry around and keep a log of all of the foods and drinks (and servings or amounts) that you consume between now and tomorrow. Record Calories if amount is known. We will use this data to calculate the total number of nutritional Calories (energy) that you consume in a 24-hour period. 2. Use product labels as much as possible to record caloric input. Energy Loss: estimating the percentage of energy lost.

Day Two: Step one: Calculating total energy (Calories) consumed through food 1. Look at your food log. Identify which day best represents your average daily consumption of food. 2. Using the computers in the classroom, go to https://www.supertracker.usda.gov/foodtracker.aspx 3. Using your log and the day you picked as most representative of what you consume on average, enter each of the items that you have eaten over the past 24 hours. Be sure to enter everything and approximate quantities accurately. For instance, if you had cereal, be sure to include the milk as well. 4. For each food that you’ve entered, add it to your running total. You should also write these down on your food log (just in case the website crashes). 5. Once you have entered everything from your log, look on the right side of the screen to find the total calories eaten. This is the total amount of energy that you have consumed in the past 24 hours. Enter this amount in your lab notebook as Total energy consumed (food Calories or “kilocalories”).

Step two: Measuring heat loss from your hand

1. Obtain a test tube and carefully add 15 mL of room temperature water. Set in rack. 2. Insert the Vernier temperature probe or glass thermometer into the test tube. 3. Without holding the test tube, record your initial water temperature in the data table below. 4. Hold the test tube in your hand so that it completely covers the area of the test tube where the water is. Hold for 10 minutes. 5. Make qualitative observations regarding your trial, but also look around at others? Are they following the protocol? Do you see differences? 6. After 10 minutes, record your final water temperature in a data table similar to the one below (in your lab notebook). 7. Pour water out into sink and place test tube upside down on test tube rack.

Initial water temp (ºC) Final water temp (ºC)

Step three: Estimating total heat loss (calculators needed). Consult the calculation worksheet on the next page to complete this section. Energy Loss: estimating the percentage of energy lost.

Calculating total heat loss: Perform these calculations in your science notebook showing all work. Don’t forget units.

1. Calculate the total change in water temperature (T) by subtracting the initial temperature from the final temperature:

______- ______= ______final temp initial temp T (ºC)

2. A calorie is a unit of energy equal to the amount needed to increase 1 mL of water by 1º Celsius. Since we used 15 mL of water in this lab, we need to calculate the total amount of energy lost by your hand in 10 minutes:

______x ____15__mL____ x 1 calorie/(mL* ºC) = ______calories T(ºC) volume of water conversion energy lost by hand

3. The palm surface of your hand is approximately 1% of the total surface area of your body 1. Thus, to estimate your total surface area, you would multiply the surface area of your palm by 100. In order to estimate the total amount of heat you lost in 10 minutes, we will assume that you can multiply the energy lost through your hand by 100 (you will discuss problems with this assumption and others later).

______x 100 = ______calories energy lost by hand total body heat loss (10 min)

4. Since we only measured heat loss over a period of 10 minutes, we need to estimate the total heat lost by your body over the course of an entire day (24 hours). 10 minutes is 1/6 of an hour, so we will multiply total body heat loss by 6 to estimate heat lost in an hour and then multiply by 24 to estimate heat lost in a day.

______x 6 x 24 = ______calories total body heat loss (10 min) total body heat loss (24 hours)

5. The energy listed on food labels is actually kilocalories (1000 calories). Therefore we need to divide the energy calculated from step 4 into kilocalories before we can use them to figure out how much of the food energy is lost.

______/ 1000 = ______kilocalories total body heat loss in calories (24 hours) total body heat loss (24 hours)

6. Finally, we need to calculate the percentage of energy consumed (through food) that was lost by heat. To do this, divide the amount of energy lost through heat (kilocalories in 24 hours) by the amount of energy consumed as food (kilocalories in 24 hours) and multiply by 100 (to convert to a %).

______/ ______x 100 = ______% total body heat loss (24 hours) total energy consumed % energy lost to heat

1 Sheridan, et al., The Journal of burn care & rehabilitation, 1995, vol. 16, no 6, pp. 605-606. Energy Loss: estimating the percentage of energy lost.

In addition to your calculated energy loss (%), write an ANALYSIS section of the lab, using the CHS LAB REPORT FORMAT. Include the following in your notebook:

Explain what should have happened  Identify what should have happened including a discussion of energy loss through food chains, energy pyramids or trophic levels.  What percent of your consumed calories should you have lost? Explain what actually happened  Summarize data and estimated energy loss (%). Remember to discuss your trial but realize the class averages are more important. Explain why these results occurred by incorporating background information  What made the water temperature increase?  Where does all of your energy come from?  Is all the energy in food incorporated into a living thing? Is an organism 100% efficient? Why not? Use simple statistics to explain data  Analysis of quantitative data includes simple statistics: e.g. percentage change, comparison to predicted value. Was there a lot of variation in the percentages calculated among the groups? State likely human errors and how these affected the data  What did go wrong? What could’ve gone wrong? Explain. Be as thorough as possible in examining the possible human errors. Link suggestions to HOW each would affect the percentage calculated. What could have had the most impact on the results?

Explain how the experiment could’ve been done differently  Was this a good model for simulating energy loss through an ecosystem? Why or why not?  Discuss the pros and cons (strengths, limitations and problems) of this simulation/estimation  What could be done differently to improve this simulation?

Write a CONCLUSION for the lab, again referring to the CHS format. RECORD in your notebook and be sure to include the following:

 Re-state your prediction and explain how your calculated value compares (cite the actual numbers)  Summarize how well the protocol helped answer the fundamental question.  What are two additional questions that could be asked to investigate energy loss (FQ)?