Enzymes Drive Reactions

Overview

In lesson 15 of the unit Cells: The Basis of Life, students examine how enzymes enable essential biochemical processes in cells. They build on prior learning about cell structures and reactions by explaining enzyme specificity and planning a safe catalase investigation involving hydrogen peroxide.

Learning intentions

Students will:

• Explain that enzymes are biological catalysts that speed up reactions without being consumed.
• Describe how an enzyme’s active site gives it specificity for a substrate.
• Explain how temperature and pH can affect enzyme activity.
• Develop a testable hypothesis and identify independent, dependent and controlled variables.
• Apply safe handling, risk-management and disposal procedures when planning an investigation.

Success criteria

• I can explain how an enzyme and substrate interact at an active site.
• I can describe how temperature and pH may change enzyme activity.
• I can write a hypothesis using a clear “If… then… because…” structure.
• I can correctly identify the independent, dependent and controlled variables in an enzyme investigation.
• I can identify appropriate safety and disposal procedures.

Curriculum links

• Students explain how cell structures enable biological processes needed for life, including biochemical processes.
• Students explain how cells, tissues and systems contribute to complex multicellular organisms.
• Cell structures and functions, cells and their environments, and biochemical processes are addressed through enzyme action and investigation planning.
• Scientific investigation skills are developed through hypothesis formation, variable identification, risk management and evidence collection.

Lesson structure (60 minutes)

1. 0–5 min · Hook and retrieval. Teacher opens with the enzyme hook slide showing the question “Why does pineapple stop some jellies from setting?” and briefly revisits organelles and the role of proteins. Students complete a quick think-pair-share, then suggest what a catalyst might do.

2. 5–17 min · Direct teaching: enzyme action. Teacher uses the enzyme explanation slides to model enzyme, substrate, active site and product, emphasising that enzymes lower activation energy and are not used up. Students annotate the enzyme concepts and investigation worksheet with a labelled enzyme–substrate diagram and write one sentence explaining specificity.

3. 17–27 min · Temperature and pH reasoning. Teacher presents temperature and pH diagrams in the temperature and pH slides, explaining that changes can alter enzyme shape and active-site function; distinguish denaturation from temporary slowing. Students interpret two simple activity graphs on the graph interpretation questions and justify which condition is most favourable.

4. 27–39 min · Investigation scenario and hypothesis. Teacher introduces catalase breaking down hydrogen peroxide into water and oxygen, using the catalase investigation introduction. In groups of four, students choose one factor to investigate—temperature or pH—then complete the question, “How does ___ affect the rate of catalase activity?” on the hypothesis and variables planner. Groups write an “If… then… because…” hypothesis.

5. 39–51 min · Variables, method and safety planning. Teacher models a fair test and demonstrates how oxygen production could be measured using foam height after a fixed time, without students handling chemicals yet. Groups identify the independent, dependent and at least three controlled variables, then record a brief method and risk controls on the variables, method and safety table. Teacher checks that students include eye protection, careful use of dilute hydrogen peroxide, no tasting, immediate reporting of spills, handwashing and teacher-directed disposal.

6. 51–57 min · Peer review and scientific discussion. Teacher displays the checklist in the peer-review and discussion slides. Groups exchange plans with another group and check whether the hypothesis is testable, the variables are correctly identified, the method is repeatable and the safety procedures are suitable. Students make one specific improvement and return the plan.

7. 57–60 min · Plenary and exit check. Teacher uses the plenary slide to pose three questions: “What makes an enzyme specific?”, “What happens if an enzyme denatures?” and “Which variable will your group change?” Students complete the final exit response on the exit reflection: define enzyme, identify one variable in their investigation and state one safety procedure.

Resources

• the enzyme investigation slide deck
• the enzyme concepts and planning worksheet
• Dilute hydrogen peroxide, catalase source such as potato or yeast, test tubes and measuring equipment for teacher demonstration
• Thermometer, water baths or temperature-controlled containers if available
• pH solutions or buffer solutions if available
• Safety glasses, gloves, trays and spill-management materials
• Whiteboard and markers
• Access to school laboratory risk assessment and disposal procedures

Assessment

• Circulate during diagram annotation and graph interpretation, questioning students about active-site specificity and denaturation.
• Check group planning for a logical hypothesis, correctly identified variables, measurable data and appropriate controls.
• Collect or photograph the completed worksheet, using the exit response to identify misconceptions before the practical investigation in the next lesson.

Differentiation

• Provide a word bank and sentence starters: “The active site is…”, “If the temperature increases, then… because…” and “The dependent variable is…”.
• Give developing writers a partially completed enzyme diagram and a variable-identification example; allow oral explanation before written recording.
• Support EAL/D students with labelled visual models, explicit pronunciation of key terms and mixed-language collaborative grouping where appropriate.
• Extend students by asking them to predict the shape of an activity graph, explain why extreme pH may denature an enzyme, or propose how repeated trials would improve reliability.
• Assign practical roles within groups—facilitator, recorder, safety officer and reporter—to support participation and executive functioning.