Identification of macromolecules in food is a standard introductory high school biology lab. The intent of this article is to describe the conversion of this standard cookbook lab into an inquiry investigation. Instead of verifying the macromolecules found in food, students use their knowledge of the macromolecules in food to determine the characteristics of specific biological indicators.

During the study of biochemistry, high school biology teachers frequently include a laboratory exercise in which students are asked to determine what macromolecules are present in various food sources. However, these activities typically do not allow students to truly discover anything, for they are merely verifying information that is already possessed. This type of cookbook activity allows students to simply follow the steps in a predesigned activity in which there is one correct answer.

As inquiry has begun to be introduced into science curricula, macromolecule labs have transformed into “whodunits” that give students an alternative reason for completing the activity. These problem-based activities are designed to increase engagement, but they often fail to stimulate the development of problem-solving skills. Although they provide another reason for completing the lab, there is still one correct answer and one way to complete the lab. Initial forays into inquiry can cause stress for students who prefer one correct answer, and for teachers who have established patterns of experimentation and evaluation, and therefore many labs are reworked to the “whodunit” format in the name of inquiry. Despite the unease of students and teachers, true inquiry stimulates engagement and development of higher-order thinking, because students must analyze factual information to generate scientific argument.

In transforming the macromolecules lab into an inquiry experiment, teachers increase student engagement as they ask students to generate a credible experiment in which they must plan and conduct a simple investigation (Corder & Slykhuis, 2011). Students use the data gathered from the experiment to offer a supported and logical explanation. In the following investigation, students conduct a series of at least two experiments to solve the problem of the missing indicator labels.

Teacher Notes

The idea of students randomly adding chemicals to solutions can be frightening. To reduce uncertainty and improve the outcome, it is imperative that the teacher ensure an experiment design that follows safety precautions. Standard lab safety procedures should be followed, including goggle use and the use of caution when working with hot plates. Pay attention to the material safety data sheets for each of the chemicals used in the lab (Figure 1).

Figure 1.

Information from material safety data sheets for chemicals used in this lab.

Figure 1.

Information from material safety data sheets for chemicals used in this lab.

Before allowing students to proceed with the investigation, it is necessary to approve the experiment design. This is your opportunity to discuss the experiment with the student groups and ensure that they understand the purpose of the experiment. Through discussion, you can determine whether the students have been able to design an experiment with appropriate safety concerns, controls, variables, and trials to increase the probability of informative data.

In this experiment, biuret will be the indicator for proteins; it turns purple in the presence of proteins. Benedict’s solution is used to test for simple sugar; when Benedict’s solution and a sugar are heated, the solution turns orange. Iodine turns purple in the presence of a starch.

Equipment & Supplies

Although the students are doing various experiments to solve the problem, the equipment and supplies needed are very standard:

  • Indicators in dropper bottles

  • Food sources

  • Pipettes for each food source

  • Hot plate

  • Protective gear to protect hands from heat

  • Test-tube rack

  • Variable number of test tubes, depending on experiment design

  • Test-tube clamp

  • 250–400 mL beaker for a water bath

The Activity

Inform students that the most common organic compounds found in living organisms are lipids, carbohydrates, proteins, and nucleic acids. Common foods that consist of plant materials or materials derived from animals are also combinations of these organic substances. Simple chemical tests with a substance called an “indicator” can be conducted to determine the presence of an organic compound. An indicator will react with a particular substance in a solution. A color change for an indicator is usually a positive test for the presence of an organic compound. Unfortunately, someone has lost the key to tell us what each of the indicators signifies. Present students with two problems: (1)What are the characteristics of a positive reaction? (2) What does each indicator indicate?

Explain that there are three indicators – two different carbohydrates and a protein. The two carbohydrates that we have indicators for are glucose (a specific monosaccharide) and starch (large complex chains of glucose molecules). The presence of one of these carbohydrates does not signify that the other must be present also. Give students the information for each indicator, including instructions for use and material safety data sheets (Figure 1). Ask students to generate a methodology or procedure for solving each problem with appropriate variables and controls. The beauty of this method is the generation of ideas. Different groups are able to design different experiments to solve the problem. There are multiple ways to design the experiment.

Provide a variety of food sources so that students can design an experiment. Suggested food sources are included not just for their reaction, but for the ease of determining a reaction. For example, chicken is a better option than beef or liver because of the ease of observing a positive reaction. Certain food sources are suggested because of their lack of reaction. The suggested items are

  • Milk

  • Clear lemon-lime soda

  • Corn starch

  • Egg white or albumin

  • Tofu

  • Egg yolk

  • Wheat gluten

  • Soda crackers

  • Instant potatoes

  • 10% sucrose solution

  • Chicken

  • Tuna

  • Pasta

  • Rice

Student Experimental Examples

Problem 1

Students are to determine the characteristics of a positive reaction. Present students with a master mix of all the food sources so that they have a positive reaction to all three indicators. Students will need to have a negative control to compare with this positive master mix. This should be a substance that would not react to any indicator and does not contain macromolecules.

Problem 2

Using prior knowledge of the organic composition of food sources, students predict which macromolecules could be found in the various food sources. A chart can be included to stimulate thinking (Table 1). Students should realize that some food sources contain multiple macromolecules. This should influence their choice of food sources for each indicator test.

Table 1.

Possible macromolecules.

Food ItemGlucoseLipidProteinStarch
Milk     
Clear lemon-lime soda     
Corn starch     
Egg white or albumin     
Tofu     
Egg yolk     
Wheat gluten     
Soda crackers     
Instant potatoes     
10% sucrose solution     
Chicken     
Tuna     
Pasta     
Rice     
Food ItemGlucoseLipidProteinStarch
Milk     
Clear lemon-lime soda     
Corn starch     
Egg white or albumin     
Tofu     
Egg yolk     
Wheat gluten     
Soda crackers     
Instant potatoes     
10% sucrose solution     
Chicken     
Tuna     
Pasta     
Rice     

Students then use this information to design an experiment. They might choose to test every food substance with every indicator. Students might also decide to test a small subset of the food with each indicator. In this example, a group of students might decide to test chicken, tuna, and tofu with each indicator, and they might hypothesize that the indicator that has a positive reaction to each substance is the indicator that signifies a protein. A group of students might also tackle the problem as an elimination problem in which two indicators are identified through experimentation and the third indicator is determined through logic, which is then confirmed through experimentation. The variations are many but not overwhelming.

Data & Analysis

Despite the fact that the students are all performing different experiments, they will all be generating similar data. Each experiment will generate information regarding the nature of a food source as indicated by a negative or positive reaction (Table 2). Students at the high school level often do not realize that the data generated in an experiment is a matter of fact. It is often the analysis of the data, or the conclusions drawn from the data, that lack the logical extension necessary for demonstration of understanding. The reliability of data in this experiment can be affected by many factors, from the techniques of the students to the cleanliness of the lab equipment.

Table 2.

Reaction of food items to different indicators.

Food ItemBenedict’sBiuretIodine
Milk    
Clear lemon-lime soda    
Corn starch    
Egg white or albumin    
Tofu    
Egg yolk    
Wheat gluten    
Soda crackers    
Instant potatoes    
10% sucrose solution    
Chicken    
Tuna    
Pasta    
Rice    
Food ItemBenedict’sBiuretIodine
Milk    
Clear lemon-lime soda    
Corn starch    
Egg white or albumin    
Tofu    
Egg yolk    
Wheat gluten    
Soda crackers    
Instant potatoes    
10% sucrose solution    
Chicken    
Tuna    
Pasta    
Rice    

Despite the fact that qualification of data exists in an either/or environment, contradictory data can result from a lack of experience or from cross-contamination that decreases reliability. Experimental reliability increases through repeatability and classroom collaboration. This is facilitated in the classroom through aggregation of student data sources so that students can compare individual data to group data. Both data sets, individual and composite, are significant in drawing conclusions. Analysis of the data is achieved through analysis of the congruence of individual data to class data.

Things That Make Students Say “Hmm?”

Although very simple in the experimental delivery, the list of materials throws a few “curve balls” to increase student questioning. Students will assume that the indicator that has a positive reaction to glucose will have a positive reaction in the sugar water. Although sugar water can have a slight positive reaction to the Benedict’s solution, it is not a strong reducing sugar and, thus, does not cause a complete reaction. Likewise, students will assume that wheat gluten is a starch because of its name, despite the fact that it is a protein. These “data gems” cause students to question experimental results and ask questions, which further drives student inquiry.

Variation

This experiment works best in a 90-min block; however, the inquiry can be divided over several days with a shorter time span. Teachers are often pushed for time, and flexibility in experimentation is important. This experiment can be separated so that each group has only one indicator to test, and then the information from separate groups is compiled to encourage consensus. Day 1 can be set aside for defining a positive and a negative control as well as for experiment design. Day 2 can be used for implementation of experiment design, and a third day can be added for confirmation of data or retesting.

Indicators can also be labeled as varieties 1, 2, and 3, with associated warnings. Industrious students who are accustomed to finding the right answer will use the Internet to research the indicators. Then, using that information, they will adjust their data to reflect what they know to be the correct data. Elimination of the names “biuret,” “Benedict’s,” and “iodine” will allow the students to enter the lab without preconceived notions of the correct answer.

Often science teachers feel the need for students to fully exercise the scientific method through the production of a full write-up, including questioning, hypothesis generation, identification of variables, methodology, data collection and analysis, and conclusions. Consider focusing on one or two of the science process skills for evaluation of the activity (Wilke & Straits, 2006). This will allow you to emphasize areas where you feel your students need the most work without requiring full evaluation.

Conclusions

Although students can experiment and gather data, it is the interpretation of the data that is important for fostering understanding. Teachers sometimes fail to realize that students can garner as much learning from mistakes in experiments as they can from successful experiments. It is for this reason that students must make conclusions from experimental data. Using data they have gathered in an experiment, students might conclude that Benedict’s is an indicator that signals the presence of a protein. Although this conclusion would be incorrect, if the students could support it through logic and data, the teachers would have a powerful opportunity for constructive advancement of student understanding. When asked to defend their position with data, students must build a mental list of the supporting facts. Through classroom discussion after an inquiry experiment, students can then debate the value of their conclusions with their peers in class and begin the scientific dialogue that is important in modern science. The job of the teachers is to foster this dialogue and encourage expression so that students can overcome their fear of being incorrect and realize that even in being incorrect they have actually grown and learned.

Inquiry, as a methodology, fosters student growth where cookbook labs fail. Although inquiry can seem a daunting task to a science teacher, it increases student engagement and stimulates mental activity in solving problems (Corder & Slykhuis, 2011). Engagement in inquiry is not simply designing experiments or asking questions. It is teacher involvement in follow-up discussions that will stimulate the most student growth. As teachers, we must prepare all students to be able to solve problems, and this is best fostered through inquiry experimentation.

Acknowledgments

The development of this activity was supported in part by the Clemson University SC Life project, funded by grants from the Precollege and Undergraduate Education program of the Howard Hughes Medical Institute.

References

References
Corder, G. & Slykhuis, J. (2011). Shifting to an inquiry-based experience. Science & Children, 48(9), 60–63.
Wilke, R. & Straits, W.J. (2006). Developing students’ process skills in today’s science classroom. Texas Science Teacher, 35(1), 11–16.