Materials & Prep
Prepare two labeled test tubes containing equal amounts of potato catalase extract. Keep one at room temperature and heat the other thoroughly in a hot-water bath before class. Prepare equal volumes of hydrogen peroxide for the teacher demonstration. Project or copy the data table in the Guided data analysis section and provide a half-sheet with spaces for claim, evidence, and reasoning. Confirm the demonstration's hydrogen peroxide handling and disposal procedures against school and local requirements; the teacher should handle the peroxide.
Opening prediction
AskWhich tube will produce more foam when the same amount of hydrogen peroxide is added: the room-temperature catalase extract or the thoroughly heated extract? Students individually circle a prediction, then write one reason. Require them to commit before seeing the result. Prompt a quick recall: What does an enzyme do, and what part of an enzyme must fit the substrate for the reaction to occur?
DemonstrateAdd equal amounts of hydrogen peroxide to the two extracts and have students observe foam height for 60 seconds. The room-temperature extract should produce much more foam than the heated extract. Students record only what they observe first: foam height and time. Do not accept “the enzyme died” as an observation. Tell students they will use data to explain what actually changed.
Direct instruction
ExplainEnzymes are proteins with a particular three-dimensional shape. The active site has a shape that allows the substrate to bind, so the reaction can occur. Low temperature usually slows particle movement and collisions, but it does not usually destroy the enzyme's shape. Increasing temperature can increase activity until an optimum is reached. Beyond the optimum, heat disrupts bonds that maintain the protein's shape. The active site changes shape, so the substrate no longer fits as well and the reaction rate falls.
AnalogyTreat the active site like a precisely shaped lock. A low temperature makes the lock and key move more slowly, but the lock still fits. Excessive heat warps the lock, so the key cannot fit correctly. The enzyme has not “died”; its protein shape has changed. This shape change is called denaturation.
ModelA pH change can also alter charges and bonds within the protein. That changes the active site's shape. Each enzyme has a pH range in which its shape works best, so both very acidic and very basic conditions can reduce activity.
DisplayEmphasize the difference between an observation and an inference. “The heated tube produced 0.5 cm of foam in 60 seconds” is an observation. “Heat changed the enzyme's shape” is an inference supported by the low activity after heating.
Guided data analysis
Display
Catalase activity measured as foam height after 60 seconds All trials used the same enzyme concentration and hydrogen peroxide amount. For the temperature trials, pH was 7. For the pH trials, temperature was 37°C.
Temperature (°C) Foam height (cm) 5 0.8 20 3.7 30 7.2 37 10.0 45 8.4 60 2.0 80 0.3
pH Foam height (cm) 3 0.5 5 4.1 6 8.0 7 10.0 8 8.7 9 5.0 11 0.4
Think aloudI first identify the largest value, not just the condition that appears in the middle of the table. The largest temperature value is 10.0 cm at 37°C, so 37°C is the temperature optimum in this data. At 60°C, the value is 2.0 cm. Compared with 10.0 cm, that is an 8.0 cm decrease, or an 80% decrease. I should not say the enzyme stopped working completely because the value is still 2.0 cm. The evidence supports greatly reduced activity.
Have students work with a partner to identify the pH optimum and describe what happens on either side of it. Ask: What is the evidence that both temperature and pH have an optimum rather than simply making activity increase or decrease in one direction?
Check for understandingStudents hold up or write one of three choices for 60°C: “faster,” “slower because molecules move less,” or “slower because the protein shape has changed.” Ask two students to justify the third choice using the data. Clarify that the low activity at 60°C is not explained by molecules simply moving more slowly.
Independent CER analysis
WriteStudents complete the following claim-evidence-reasoning response: “The catalase optimum in these data is 37°C and pH 7. Explain what happens when temperature rises above the temperature optimum or pH moves far from the pH optimum.” They must include one temperature value, one pH value, and the words active site, shape, substrate, and reaction rate.
ScaffoldProvide this organizer for students who need it: Claim: “Catalase works best at .” Evidence: “At , the foam height was cm, while at it was cm.” Reasoning: “This suggests that changes the enzyme's ; therefore the cannot bind as effectively and the reaction rate .” Students may first annotate the two largest and two smallest values in the table.
CirculateLook for the misconception that any temperature above room temperature damages an enzyme, and ask, “What does the 37°C value show?” Also look for students treating foam height as a direct measurement of enzyme molecules. Clarify that foam height is the activity measure used as evidence in this investigation.
ExtensionStudents who finish early explain why the 5°C result should not automatically be called denaturation. They propose a follow-up test using the same cold enzyme sample after it returns to 37°C. A strong response predicts that activity could recover if the shape was not permanently changed, unlike the heated sample.
Closing check
Exit ticketAnswer both parts independently. 1. Identify the temperature optimum and pH optimum from the data, with the values that support each answer. 2. Explain why catalase activity decreases at 60°C and pH 11. A complete response must state that extreme conditions change or disrupt the protein's shape, alter the active site, reduce substrate binding, and lower the reaction rate. Students may use the sentence frame “The enzyme does not simply die because…” to replace the class's original wording with a scientifically accurate explanation.