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Idea Bank

Teacher Demonstration—Student Exploration

Inquiry-influenced labs can take many forms, from weeks-long projects to partial-period investigations. To increase student autonomy and critical thinking without sacrificing much class time, our biology team has attempted a new approach, which we hope can give an inquiry flavor to tried-and-true labs. This new approach follows a generic sequence of teacher demonstration followed by student exploration. This brief write up will describe how we’ve implemented this approach with two common biology labs: Environmental Effects on Catalase Reactions and Determining the Sucrose Concentration in a Potato. Although we describe approaches to these two common labs, there are many other variations that can be done by implementing the “teacher demonstration—student exploration” sequence.

Environmental effects on catalase reactions

Teacher demonstration

Toward the end of a class period, the teacher demonstrates how catalase (an enzyme extracted from ground chicken livers) breaks down hydrogen peroxide in a graduated cylinder, and how the height bubbles can be measured in the first five seconds to get an idea of how quickly the enzyme worked. Procedures for the demonstration include blending a piece of chicken liver in water and keeping the solution on ice until class, then adding approximately 1 ml of this liver (catalase) solution to 1 ml of hydrogen peroxide that has already been placed in a graduated cylinder along with a drop of dishwashing soap.

After students see the bubbling reaction, they are told that certain variables can impact the ability of the enzyme to catalyze this reaction, such as temperature, acids/bases, and salt concentrations. Their job the next day will be to determine how these factors influence the rate of reaction.

Student exploration

The following day, the teacher reviews safety considerations and reminds students to wear vented chemical-splash goggles and aprons. Students then work in pairs on how to design an experiment to test the effects of one of these variables using the materials that are available in the classroom. Materials provided include ice, thermometers, hot plates, beakers, different acids and bases, graduated cylinders, hydrogen peroxide, various concentrations of salt solutions, disposable pipettes, and a sampling of other items that will be of no use to the students for this lab, such as digital balances.

Once students have designed their experiment and correctly identified their dependent and independent variables, the teacher gives approval for the students to begin their investigation. At this point in the experimental process, the teacher should guide students while still allowing for students to make safe mistakes. The teacher should be able to assess how well students are able to identify variables, control for non-tested variables, and design a lab that will give reliable results.

Although students struggle at first with this openness to procedures, they quickly catch on and try ideas with the encouragement of their teacher. Because each student pair is only testing one variable, their experiments can be completed a few times within the class period, each time with student-determined refinements. Once they feel confident in their findings, they use a whiteboard (or poster board) to describe their experiment, findings, and conclusions.

When all the boards are in the front of the room, the teacher can then lead a discussion as to what were strengths and weaknesses of different experimental approaches, and what they can learn from these experiments on factors that affect enzymatic action. Items teachers can assess from these whiteboard presentations would include the correct identification of variables, controlling for non-tested variables, reliability of the data based on the number of trials, etc., student conclusions, and student ideas on how to make the experiments stronger.

Determining the sucrose concentration in a potato

Teacher demonstration

At the beginning of a class, the teacher will weigh three dialysis bags containing 0.2 M sucrose, writing their intial masses on the board. She will then place each of the bags into three different beakers containing 0.0 M sucrose, 0.2 M sucrose, and 0.4 M sucrose, respectively. The teacher will then continue on with a lesson (perhaps a discussion of osmosis, etc.).

Toward the end of the class period, the teacher will weigh each of the three bags again, perhaps first having students predict if the masses have increased or decreased, and students will use the data to calculate the mass gained or loss in each situation. A class discussion can then guide students to the idea of water entering or exiting the bags based on osmosis in hypotonic, isotonic, and hypertonic solutions. Students are then told that they will use what they’ve seen in today’s demonstration to determine the sucrose solution of a potato in tomorrow’s lab. The teacher will tell them that one of the differences between the dialysis bags and the potato is that the difference seen in the dialysis bags happened in a class period, whereas the potatoes will require an overnight incubation. They are given time to discuss this with their partner, and told to continue thinking about it for homework.

Student exploration

The following day, students work with their partner to design a lab that will determine the sucrose concentration of a potato. To assist students and save time, they will have access to multiple concentrations of sucrose solutions ranging from 0.0M to 0.8M, pre-cut 1-inch potato pieces (created with a french fry slicer and a knife), paper cups, electronic balances, and few other non-related items to keep their minds critically examining tools that would be needed for their experiment.

Although students can struggle at first, and although they often need to make a few attempts in order to get the set-up correct, they do arrive at various sophisticated ways to determine the sucrose concentration in potatoes, such as determining the initial mass of their potato pieces, then placing an equal number of potato pieces in different concentrations of sucrose to sit overnight. As seen with the dialysis bag demonstration, the solution that causes the potato to lose or gain the least amount of weight is the concentration that most closely matches the internal sucrose concentration inside of the potato.

The following day, students determine the final mass of their potato pieces for their data, then prepare to share their experiments with the class. Students write their experimental design, results, and conclusion on whiteboards that are placed at the front of the classroom. The teacher then leads a discussion on experimental design differences and what can be learned from the results. Alternatively, students can present their own work. The whiteboards or the student presentations can be used to assess how well students not only understand experimental design (such variables, reliability, etc.), but also how close students’ findings of the sucrose concentrations of the potato came to the class-accepted values.

Although this teacher-demonstration-student-exploration approach to changing common cookbook labs into labs that have a more inquiry feel may not satisfy all of the goals of scientific inquiry, it is a time-wise method for providing an opportunity for students to experience more autonomy in their experimentation, apply their knowledge of experimental design, contribute to a learning community, and publicly account for their scientific findings. Our biology team has been pleased with the results of this approach to converting labs, and we’re continuing to explore more labs that might become more inquiry-friendly through this approach.


Julie Gaubatz (jgaubatz@hinsdale86.org) is a biology teacher at Hinsdale South High School, Darien, IL.

Chemistry Pedagogy Teaching Strategies High School

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