Description:

Students will design and conduct an experiment to test their ideas about how to speed up or slow down the rate of an enzyme-catalyzed reaction. Students will have access to an array of physical and chemical factors that might influence enzyme activity. They are expected to predict how one of the factors might affect the reaction rate and test it in a high quality experiment.

The task assesses students' understanding of experimental design and the nature of good scientific investigation. Students also demonstrate their understanding of the principles governing the nature of enzyme activity in biological systems, including an understanding of the 3-dimensional specificity of enzyme/substrate interactions and the conventional concepts of what physical and chemical factors influence enzyme activity.

This task is designed to take students approximately Three hours to design and carry out the investigation and one hour to discuss progress on write-ups prior to due date. (Note that students will write up report outside of class.)

Overall Task Content Area:

Life Science

Specific Knowledge Areas:

Structure and function in biological systems

  Chemical reactions

Performance Expectations:

• conducting investigations
• using equipment
• gathering, organizing, and representing data
• formulating conclusions from investigational data

National Science Education Standards:

12 A SI 1: Abilities necessary to do scientific inquiry: Grades 9-12

1.2 Design and conduct scientific investigations. Designing and conducting a scientific investigation requires introduction to the major concepts in the area being investigated, proper equipment, safety precautions, assistance with methodological problems, recommendations for use of technologies, clarification of ideas that guide the inquiry, and scientific knowledge obtained from sources other than the actual investigation. The investigation may also require student clarification of the question, method, controls, and variables; student organization and display of data; student revision of methods and explanations; and a public presentation of the results with a critical response from peers. Regardless of the scientific investigation performed, students must use evidence, apply logic, and construct an argument for their proposed explanations.

1.4 Formulate and revise scientific explanations and models using logic and evidence. Student inquiries should culminate in formulating an explanation or model. Models should be physical, conceptual, and mathematical. In the process of answering the questions, the students should engage in discussions and arguments that result in the revision of their explanations. These discussions should be based on scientific knowledge, the use of logic, and evidence from their investigation.

12 B PS 1: Structure of atoms: Grades 9-12

1.2 The atom’s nucleus is composed of protons and neutrons, which are much more massive than electrons. When an element has atoms that differ in the number of neutrons, these atoms are called different isotopes of the element.

(Use the "hot" link on the PALS home page to check the full text of related National Science Education Standards, if desired.)

General Instructions to the Teacher:

This task is designed to take students approximately 2 periods in class for discussion, instruction, Internet searches (if used). .

Students should be ready to work as soon as periods begin. A central supply area, if needed, should be easily accessible. All supplies should be clearly labeled.

Materials for " Catalase Enzyme":

The student will need:

• Fresh beef liver ( from the grocery store-(frozen will work, but enzyme activity will be a bit weaker)).
• Hydrogen peroxide ( 1.5% concentration).
• Sufficient test tubes, small graduate cylinders, tube racks, forceps so that each students has enough to satisfy her experimental requirements.
• An array of prepared physical and chemical materials. Some examples are:
• Boiling water, ice water, body temp. water (~37^oC), room temperature (~20^oC) water
• Acids and bases - make pH solutions ahead of time
• Alcohol
• Sugar and salt solutions
• Caffeine
• Aspirin and ibuprofen.
• Use a 10%detergent solution and measure bubble with a ruler.

Advance Preparation:

This investigation was designed to allow students to discover the effects of various chemical and environmental factors on enzyme activity. It is intended to come near the end of a unit on the nature, function, and importance of enzymes, and to allow students to get some hands-on experience with enzyme-catalyzed reactions.

As an introduction to this task the effect of beef liver on hydrogen peroxide are demonstrated. The highly toxic nature of H₂O₂ is explained as well as that catalase is an enzyme found in all complex creatures that destroys H₂O₂ by turning it into H₂O and O₂.

Some common comments are "why does my mom make me put this stuff on cuts?" or "Why are you supposed to gargle with it for sore throats?" This leads to discussion of how well protected humans are, and that bacteria have no catalase, so they are unprotected. The "fizz" that appears if H₂O₂ is put on a wound and what creates the "fizz" is explained. This usually gets at least some of the students interested in catalase.

Make sure that students understand that many things can affect enzyme activity, some of them have health implications ( nerve gases, for example, interfere with an enzyme that is involved in the transmission of nerve impulses), some do not. Make sure that, as the various prepared chemical and physical factors are described, that they not limit themselves to only prepared ones. Encourage students to come up with other ideas for factors to investigate, as long as they have some logical reason for wanting to examine them. It is also important to encourage students to Keep It Simple! Students shouldn't plan to experiment on a whole array of factors, they should plan instead to focus on one set of factors that they think will have an effect. Ideally, the more advanced students will look for factors that might alter the shape of the enzyme and suggest that those should slow or stop the reaction.

Students are asked to check out their question and design before they proceed. This provides the opportunity to coach those having problems through the process.

It's important to realize that the data collected by most students will be a roughly quantitative evaluation of enzyme activity rate on a scale of 0 to 5, with 4 being defined as the rate observed between room temp H₂O₂ and liver. All the students should be very familiar with this rate, and perhaps should always run a room temp. treatment as the standard control for any experiment. The data then will mostly consist of numbers along the 0-5 scale. It is somewhat subjective, but students tend to estimate accurately as long as they refer back to the "4" standard periodically.

Allow approx. 1 week for the students to complete the write-up. Because this is the first inquiry task of the year, also hand out an example of a good write up for a similar experiment and a copy of the scoring guide. Schedule some time each class period prior to the due date to review student work and to answer any questions students might have.

Safety:

• Be careful.
• Teachers and students should always exercise appropriate safety precautions and utilize appropriate laboratory safety procedures and equipment when working on science performance tasks.

Extensions/modifications:

• Students may wish to extend this procedure to examine other areas such as nearby riparian zones (contrasting those in city parks to those in rural or wild-land areas), forests (managed wooded lot vs. wild-land), or wetlands.