Lesson Plan

• Describe the Beer‑Lambert law and how absorbance relates to concentration.
• Explain how a colourimeter can monitor enzyme‑catalysed reactions that produce a colour change.
• Apply the step‑by‑step procedure to collect absorbance data and calculate initial reaction rates.
• Analyse the effect of temperature, pH or enzyme concentration on reaction rate using colourimetric data.
• Evaluate safety and best‑practice considerations when using a colourimeter in the lab.

• Colourimeter with selectable wavelength
• Standard (1 cm) cuvettes or disposable cuvettes
• Enzyme solution, substrate solution, buffer
• Pipettes and disposable tips
• Timer or data‑logging device
• Lab notebook / data worksheet
• Safety goggles and gloves
• Projector for brief mini‑lecture

Begin with a quick demonstration of a fruit turning brown to illustrate colour change in everyday life. Ask students to recall how enzymes accelerate reactions and why monitoring the rate is important. Explain that by the end of the lesson they will be able to use a colourimeter to quantify enzyme activity and will know the criteria for successful data collection.

1. Do‑now (5'): Students answer short questions on enzyme specificity and active sites.
2. Mini‑lecture (10'): Introduce Beer‑Lambert law and the principle of colourimetric measurement.
3. Safety briefing & instrument set‑up (5'): Demonstrate zeroing the colourimeter with a blank.
4. Hands‑on activity (20'): Students prepare reaction tubes, add enzyme, take initial absorbance (A₀) and record at 30‑second intervals.
5. Data analysis (10'): Plot A versus time, calculate the slope (initial rate) and convert to concentration.
6. Group discussion (10'): Compare rates under different temperatures or enzyme concentrations.
7. Exit ticket (5'): Write one key insight and one question they still have.

Summarise how absorbance data provide a quantitative picture of enzyme activity and how variables influence the rate. Collect exit tickets as a quick retrieval check. For homework, students will design a brief colourimetric experiment to test the effect of a chosen inhibitor on enzyme rate.