"What factors influence how efficiently the work of a cell is carried out?"

Goals
A. Learning Goals: This activity is designed for students to...
1. ...model the development of experimental design
2. ...analyze the data of different variables by sharing with other groups within the class.
3. ...learn to make predictions based on observations
B. Key concepts
1. Enzymes carry out the work of the cell.
C. Vocabulary words
1. Enzyme
2. Substrate
3. Active site

This activity is intended for use in a 10th grade Biology class and can also be adapted for use at the Advanced Placement/Advanced Biology level. It can be used in any size classroom as long as students are able to be placed in pairs to work through the experiment. The activity is designed as a lab investigation and should take 1-2 periods depending on the level in which the instructor wishes to carry out the investigation. This investigation is designed to be done within a unit on cellular structure and function in which cell organelles have already been discussed. This investigation would take place after a discussion of the function of enzymes has been addressed as this investigation concentrates on discovering what kinds of factors affect the action of enzymes within a cellular context.

Before this investigation is conducted with students, they will have had exposure to how an enzyme works. The purpose of this investigation is to then follow this knowledge with an exploration of the factors that might affect how well an enzyme would work in the cell under certain conditions. Materials needed for this investigation are toothpicks, ice water, metal sewing needles and a timing device with second capability. Students begin the investigation by establishing a "base rate of reaction" by being instructed to break 40 toothpicks in a pre-designated time period. This reaction is timed continuously over 3 minutes. Students work in pairs. One student is breaking toothpicks (only one toothpick at a time) and their partner is timing and recording data. Students then graph and begin to analyze their data. To encourage students to uncover factors that might affect the activity of the enzyme they are asked to choose a further investigation: 1.) enzyme concentration, 2.) substrate concentration, 3.) enzyme temperature , 4.) competitive inhibition (instructors may choose not to cover this factor in a general biology class). Students need to predict what they think will happen to their enzyme during their investigation. They will then design an experiment that will help them observe what happens to the activity of the enzyme. Throughout the development of student investigations, discussions will be held to help students uncover their misconceptions, refine experimental design, clarify the construction of data tables, etc. Students will need to design a data table to collect data during their experiment and to also graph their data. Closure will occur when students will be asked to analyze their data by discussing whether or not their experiment supported or refuted their original hypothesis. Students will be asked to compose questions they still have concerning enzymes being directed by the instructor to create at least one question that relates to cells. We will discuss some of these questions as a class.

This activity is adapted from: "Enzyme Reaction Rates Using Toothpickase" from Carolina Biological Supply Company “What factors influence how efficiently the work of a cell is carried out?” (Microsoft Word 2007 (.docx) 19kB Aug3 09)

I have found points of confusion for students when discussing how to time the experiment. Data is gathered over a continuous time period, so instructors need to pay careful attention in helping students to understand this type of data collection. Flat toothpicks work best for this lab, although the variable of substrate shape could be introduced by having some students work with round toothpicks as well. Make sure to purchase plenty of toothpicks as some groups will make mistakes and need more. Each group of students needs 5 piles of 40 toothpicks for the initial investigation, but not all toothpicks in each pile will be broken, so these can be re-used.

I have used this activity in the past, but this is different in that I used to simply ask students to predict what they think would happen if, for example, "toothpickase" was exposed to ice water for 1 minute. In this activity, I am asking students to come up with their own way of testing the affect of temperature on enzyme activity. The same is true of the other variables. I also used to give the students a list of terms (enzyme, substrate, active site, substrate concentration, enzyme concentration, reactants, products) to define before beginning the experiment. This was not particularly effective. In this version, students are simply told a reaction is taking place between the toothpicks and their hands. During the investigation, a discussion should take place concerning the terms enzyme, substrate and active site. Where this discussion happens will depend on the nature of the students.

Students will record information from this investigation in their lab notebooks. They will be assessed on the inclusion of prediction, hypothesis, description of experimental design, data collected and displayed (graph) and their discussion of whether or not their results supported or refuted their original hypothesis. This will be graded on a rubric developed by the instructor. Since I have not done this version of the lab, the rubric will probably be developed after I see what kind of student work is produced. This will allow me to make changes/alterations to this investigation for next year and therefore the rubric may look different as well.

9.4.1.2.2 - Cells and cell structures have specific functions that allow an organism to grow, survive and reproduce.