| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Biology |
| Lesson Topic: describe and carry out investigations using redox indicators, including DCPIP and methylene blue, to determine the effects of temperature and substrate concentration on the rate of respiration of yeast |
Learning Objective/s:
- Describe how DCPIP and methylene blue act as redox indicators in yeast respiration assays.
- Explain the influence of temperature and glucose concentration on the rate of yeast respiration.
- Apply spectrophotometric techniques to measure colour change and calculate reaction rates.
- Analyse data to identify optimal temperature and substrate‑saturation behaviour.
- Evaluate experimental limitations and suggest improvements.
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Materials Needed:
- Active dry yeast, glucose stock solution, DCPIP and methylene blue solutions.
- Distilled water, test tubes, pipettes, cuvettes, and timers.
- Water baths set to 15 °C, 25 °C, 35 °C and 45 °C.
- Spectrophotometer (or colourimeter) with appropriate filters.
- Lab coat, gloves, safety glasses and waste‑disposal containers.
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Introduction:
Begin with a quick demonstration of a colour change when DCPIP is reduced, linking it to cellular respiration. Review students’ prior knowledge of redox reactions and enzyme activity in metabolism. Outline today’s success criteria: students will design and conduct the assay, record absorbance data, and interpret how temperature and substrate concentration affect respiration rates.
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Lesson Structure:
- Do‑now (5’) – short quiz on redox reactions and yeast metabolism.
- Mini‑lecture (10’) – recap redox indicators and experimental variables.
- Demonstration (5’) – show DCPIP colour loss in a yeast suspension.
- Group experiment set‑up (15’) – prepare reaction tubes for one temperature series and record initial absorbance.
- Data collection (10’) – take absorbance readings every 30 s for 5 min.
- Data analysis (10’) – calculate ΔA/Δt, plot initial rates vs temperature and glucose concentration.
- Discussion (10’) – compare results, identify optimal temperature and substrate saturation, consider differences between indicators.
- Exit ticket (5’) – write one conclusion about how temperature affects yeast respiration.
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Conclusion:
Summarise the key findings that temperature has an optimal range for yeast respiration and that higher glucose concentrations increase the rate up to a saturation point. Ask students to complete an exit ticket stating the most significant factor influencing the rate. For homework, they should draft a brief proposal to investigate the effect of pH using the same indicators.
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