Unit 4: How Cells Acquire Energy

Name ______Period ___

Energy Content of Food Introduction

You are a lab technician working for NASA. Recently you were given the job of deciding what type of foods would be included in the next space mission. Four food types have been selected as possible snacks for the astronauts: marshmallows, cashews, peanuts, and popcorn cakes. You need to determine which of these four food choices has the highest energy content, while adding the least amount of mass to the mission.

Your team will test two of the food types using a method known as calorimetry. During this process, you will burn a food sample positioned below a can containing a given amount of cold water. The water temperature will be monitored during the experiment using a thermometer. By calculating the change of the water temperature, you will determine how much energy was released when the food sample burned.

Pre-Lab: Write the following in your lab notebook

(1) Biological Question for this experiment (2) Hypothesis (3) Procedure

Procedure

1. Obtain a piece of one of the two types of food assigned to you and a large paper clip used to hold the piece of food. Find and record the initial mass of the food sample and the food holder. Record your data in Data Table 1 below

2. Measure 50mL of cold water and add to the can.

3. Set up the apparatus as shown in the figure below. Use a ring and suspend the can about 2.5 cm above the food sample. Record the initial temperature of the water of Data Table 2 below:

4. Remove the food sample from under the can and use a wooden splint to light it. Quickly place the burning food sample directly under the center of the can. Allow the water to be heated until the food sample stops burning.

5. Stir the water until the temperature stops rising. Record this maximum temperature in Data Table 2.

6. Determine and record the final mass of the food sample and food holder in Data Table 1.

7. Repeat steps 2-6 for food type 2.

1 Pre-AP Biology Unit 4: How Cells Acquire Energy

TO INTERFACE

SLIT STOPPER

UTILITY CLAMP

TEMPERATURE SENSOR

STIRRING ROD

IRON RING

CAN

FOOD SAMPLE

FOOD HOLDER

Data Table 1: Mass Food Sample 1: Initial Mass of Food: Mass after Burning: Mass of Food Burned (

g g g Food Sample 2: Initial Mass of Food: Mass after Burning: Mass of Food Burned (

g g g

Data Table 2: Temperature Food Sample 1: Initial Temperature: Highest Temperature: Temperature Change (

°C °C °C Food Sample 2: Initial Temperature: Highest Temperature: Temperature Change (

°C °C °C

2 Pre-AP Biology Unit 4: How Cells Acquire Energy

Calculations:

1. Calculate the Mass of Food Burned. Subtract the final mass from the initial mass. Record in Data Table 1.

2. Calculate the Change in Water Temperature T for each food sample by subtracting

the initial temperature from the maximum temperature (T= Tmaximum-Tinital). Record the results in Data Table 2

3. The mass of 1mL of water is 1g. What is the mass of 50mL of water? This is the value of m in the equation you will use for the calculation in question #4.

4. Use the equation below to calclulate the energy content Q in kJ

5. So that we can directly compare the foods, calculate the energy content per gram. Divide Q by the Mass of Food Burned. (E = Q/ M) in kJ / g. Record in Data Table 3.

Data Table 3: Calculations Food Sample 1: Q = kJ Energy Content of Food per gram(Q/) = kJ/g Food Sample 2: Q = kJ Energy Content of Food per gram (Q/) = kJ/g

Q = (T x m x Cp) / 1000 = kJ

o Cp = specific heat capacity for water = 4.185 J/g C

m = 50 g (because 1mL = 1g, and we used 50 mL)

1 Calorie = 1kCal = 4.184 kJ 1 kJ = 0.239 Calories (kCal)

Data Table 4: Class Results Marshmallows Peanuts Cashews Popcorn kJ/g kJ/g kJ/g kJ/g

kJ/g kJ/g kJ/g kJ/g kJ/g kJ/g kJ/g kJ/g kJ/g kJ/g kJ/g kJ/g kJ/g kJ/g kJ/g kJ/g Average for each food type kJ/g kJ/g kJ/g kJ/g

3 Pre-AP Biology Unit 4: How Cells Acquire Energy

Summarize the results from the class data set

 State Conclusion (claims)  State claim(s)  Use numerical evidence to support conclusion  State hypothesis , whether you reject/accept hypothesis and why  Reflection  Error analysis  Describe errors during experiment  Describe how those errors affected your results  Describe how your ideas have changed, possible new questions that you have, or new ideas this lab caused you to think about  Describe how this lab relates to concepts taught in class or read in your text.

Answer the following the analysis questions at the end of your conclusion.

1. Which food had the highest energy content? Which had the lowest energy content?

2. Two of the foods in the experiment have a high fat content (peanuts and cashews) and two have a high carbohydrate content (marshmallows and popcorn). From your results, what conclusion can you make about the relative energy content of fats and carbohydrates?

3. Based on the data you and your classmates collected, which of the four foods tested would you suggest sending to the NASA space mission? Explain your reasoning.

4. Describe the energy transformation that took place in this experiment.

5. Was all of the heat energy given off by the burning food transferred to the water in the can? How could this experiment be improved so that more heat energy is captured by the water?

4 Pre-AP Biology