Investigating Characteristics of Enzymes and the Factors that Affect Their Function.

Jeanette Vance, The Blake School, Minneapolis, MN 55403
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Summary

In this classroom lab, students will explore the characteristics of a particular enzyme and the factors that affect its ability to catalyze a reaction. Students will look at how the enzyme catalase (source of catalase is chicken liver) affects the break down of hydrogen peroxide into water and oxygen. They design their own methods to answer the following questions: What substances contain the enzyme catalase? Why does the reaction stop? What is the effect of temperature on catalase function? And What is the effect of pH on catalase function? Students collect and analyze data to answer reflection questions. The complete a written lab summary that synthesizes data from the lab and knowledge of enzymes.

Learning Goals

1. Students will develop inquiry skills by designing and comnpleting a lab investigation to answer provided questions.
2. Students gain an understanding of the general characteristics of enzymes through exploration of a specific enzyme.
3. Students will synthesize their ideas and develop their writing skills by connecting lab data to understanding of the concept of enzymes.

Context for Use

This lab activity can be used in an introductory biology class in grades 9-12. It could easily be adapted to explore the role of catalysts in an introductory chemistry class. Students need to have a general understanding of the role of a catalyst in a chemical reaction and proteins in general. It is typically completed after covering macromolecules, specifically proteins but before moving into enzymes. The lab takes approximately two 65 minute class periods for students to complete the lab designs and collect data. By either shortening the exploration questions or requiring more precise data collection this lab could be easily adapted for various skill levels.

Description and Teaching Materials

See attachements
Pre-Lab:
Students are given an overview of the lab to read before they come to class. They are also asked to come up with a hypothesis and methods to answer the first question,"Which substance contains catalase?" as homework before the day of the lab.
Lab work: Working in groups of 2-4 students they decide on a procedure to address the first question. After getting approval by the teacher they are allowed to obtain the equipment necessary to collect data. Once they have collected data they are able to move on to address second question. Students are only allowed to conduct experiments after procedure has been approved by teacher. It is important to note that many groups will need to revise procedure to collect sufficient data to answer each question.

Reflection questions: Students work as a group to answer reflection questions analyze data

Lab summary written assessment: Each individual student provides a written summary connecting the lab to their understanding of enzymes. This is submitted as final assessment of the lab.

Materials Needed:
Container of chicken livers(found in meat section of grocery store)1 container/75 students should be enough
Test tubes
Hydrogen peroxide
Hot water bath
Ice bath
Thermometers
Stopwatches(optional)
Stirring rods
Dilute Acid and Base for pH demo
pH strips
scissors Assignment Handout (Microsoft Word 59kB Aug15 08) Lab Summary Assessment Questions (Acrobat (PDF) 42kB Aug15 08)

Teaching Notes and Tips

Common areas of confusion: Students get the terms catalase and catalyst mixed up. It needs to be reinforced that the liver is the source of the enzyme so if you are changing the environment of the enzyme you need to do something to the liver not the hydrogen peroxide(i.e. heat the liver first then add the perioxide).

The students only need about a pea sized amount of liver for each test tube. I give them a small amount of liver in a petri dish and allow them to cut pieces off to place in test tube. Because most of the data we collect is qualitative we let them pour right from the hydrogen perioxide bottle but you may want to have them measure amounts each time.

For the affect of pH on the catalase the teacher has conducted the experiment as a demo to save time and to avoid
student use of acids and bases. The students don't write a procedure but have a class discussion on how we should test this before conducting the experiment.

Assessment

During the lab most assessment is through periodic group check in and discussion. Lab groups will hand in written record of methods and reflection(either individually or as a group). Individual students are assessed by written summary(see attachement)

Standards

Grades 9-12 I.B.1-3 Scientific Inquiry
Grades 9-12 IV.A.4 Role of Enzymes in Cells
Grades 9-12 II.B.2 Chemical Reactions

References and Resources