Measuring Stored Energy in Food 

Introduction:

Plants are autotrophic organisms that utilize sunlight to make usable energy during a process called photosynthesis.  Life on earth is supported by photosynthesis.  Photosynthesis used sunlight to convert carbon dioxide and water into glucose and oxygen.  This process involves two cycles and is fairly complex.  The two cycles are cellular respiration and the Calvin cycle, and both of these involve several steps. 

During cellular respiration, organic compounds are combined with oxygen to produce ATP, yielding carbon dioxide and water as waste products.  In first step, glycolysis glucose is used to make two molecules of pyruvic acid   Glycolysis also has a net yield of two ATP molecules for every molecule of glucose that is converted.  The next step may be anaerobic, fermentation, or aerobic, the Krebs cycle.  During fermentation, NAD is regenerated and used to keep glycolysis going.  During the Krebs cycle, acetyl CoA is broken down producing carbon dioxide, hydrogen atoms and ATP.  The second process, the Calvin cycle, is where carbon atoms are bonded into organic compounds.  This is called carbon fixation.  In this experiment, the amount of energy available for use from nuts is measured, and the measuring of the energy stored in food is known as calorimetry. 

Hypothesis:

By measuring the increase of temperature in a certain amount of water, after burning a nut, then the number of calories in the nut can be determined. 

Materials:

The materials needed for this experiment are large paper clip, thermometer, soft drink can, soft drink can with openings cut into the side, mixed nuts, matches, water, pencil and paper, graduated cylinder, and an electronic balance. 

Procedure:

First, carefully, cut out two openings along the side of a soft drink can.  This will serve as the support for the second drink can that will contain water and sit on top.  Next, bend a large size paper clip so that a nut can be attached on one end and the other end will sit flat inside the cut-out soft drink can.  Thirdly, use the graduated cylinder to accurately measure 100g (100 ml) of water, and pour this water into the uncut soft drink can.  Then, use the thermometer to measure the temperature (degrees C) of the water, and record this temperature on the data table.  Next, mass the nut (g) that will be burned and record this mass on the data table.  After this, attach the nut to the bent end of the paper clip and carefully set the clip and nut into the cut-out soft drink can on bottom (make sure the cans are sitting on a flat, nonflammable surface).  Next, carefully light the nut using a match and record the change in water temperature as the nut burns.  Record the final (highest) water temperature as the nut burned.  Then, measure the mass (g) of the remaining nut and record this in the data table.  Finally, complete the data table by calculating the change in mass of the nut and the temperature of the water.  If time remains repeat this experiment with a different type of nut but remember to always start with cold water and to take the initial and final water temperature and mass of the nut. 

Results:

The results of the Calorimetry experiment are shown in the two charts. 

Data Table

 Analyze data from nut Calorimetry    

 Questions: 

1.  What is the relationship between matter and energy?  The greater the matter, the greater the energy. 

2.  What do we call stored energy and where is energy stored in compounds such as glucose?  Stored energy is stored as calories and the energy is located in bonds. 

3.  Discuss what happened to the energy stored in the nut.  Bonds were broken and energy was released. 

4.  Why was the mass of the nut less after burning?  (Remember matter can’t be destroyed in chemical reactions.)  The mass of the nut was less after burning because the matter of the nut was released into the atmosphere as a result of the heat from the flame as heat energy..  The heat gave enough energy for the chemical bonds of the nut to break and the matter released.  The only atom not released was carbon, which is why the nut still had mass. 

5.  How do our bodies make use of this process?  When we take in food, our bodies take the energy from the foods we eat, like nuts, similarly to how the heat of the flame did because bonds are broken,, and use that energy and turn it into energy we use for all of our life functions. 

Error Analysis:

A couple of errors could have affected the results in the experiment.  First of all, part of the nut could have broken off of the nut while the students were handling it.  The students also could have forgotten to press tare on the electronic balance while measuring the nut’s mass.  Finally, the entire nut might not have been burned even though it looked like it had. 

Discussion and Conclusion:

The temperature of the 100 mL of water increased while the nut was being burned.  The heat energy was great enough to raise the temperature of the water by 21 degrees Celsius.  The mass of the nut before it was burned was 1.8g while the mass of the nut after burning was 0.1g.  This means that the mass of the nut burned was 1.7g.  It takes 100 calories to raise the temperature of 1 mL of water by 1 degree Celsius which means that 2100 calories were needed to raise the temperature of the water by 21 degrees Celsius.  Also, the nut had 1166.67 calories per gram.  By using the mass of a pecan nut and temperature of 100 ml of water, it is possible to find how many grams per calorie in a pecan nut.  This experiment measured the amount of calories stored in a pecan nut by using a process called calorimetry. 

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