| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Biology |
| Lesson Topic: describe and carry out investigations, using simple respirometers, to determine the RQ of germinating seeds or small invertebrates (e.g. blowfly larvae) |
Learning Objective/s:
- Describe the concept of respiratory quotient (RQ) and its significance in metabolism.
- Explain how a simple respirometer measures O₂ consumption and CO₂ production.
- Calculate RQ from experimental data for germinating seeds or blowfly larvae.
- Analyse RQ values to infer the primary metabolic substrate being utilised.
- Evaluate the advantages and limitations of the simple respirometer method.
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Materials Needed:
- 100 mL graduated cylinder (respirometer chamber)
- U‑tube water manometer with coloured water
- Stopcocks
- Thermometer
- Stopwatch/timer
- Distilled water
- Germinating wheat/barley seeds or blowfly larvae
- Filter paper, Petri dishes, fine brush
- Data worksheet and calculator
- Safety gloves and lab coat
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Introduction:
Begin with a quick demonstration of a sealed syringe changing volume as a student breathes, sparking curiosity about invisible gas exchange. Review prior learning on cellular respiration and the RQ formula. Explain that today’s success criteria are to construct a simple respirometer, record gas‑volume changes, and compute an accurate RQ for a chosen organism.
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Lesson Structure:
- Do‑Now (5’) – Answer: “If a plant consumes O₂ and releases CO₂, what RQ would you expect?” Brief class discussion.
- Mini‑lecture (10’) – Recap respiration, introduce RQ, show diagram of a simple respirometer.
- Build & calibrate respirometer (15’) – In groups assemble chamber, manometer, stopcock; fill manometer, check for leaks.
- Prepare organisms (10’) – Soak seeds or weigh larvae, place them in the chamber with moist filter paper.
- Data collection (30’) – Run experiment for 30 min, record water level every 5 min; repeat for three trials.
- Calculations (10’) – Convert Δh to ΔV, compute O₂ consumed, CO₂ produced, and RQ; average results.
- Interpretation & discussion (10’) – Compare RQ to theoretical values, infer substrate, discuss sources of error.
- Exit ticket (5’) – Write one sentence stating the RQ found and what it indicates about metabolism.
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Conclusion:
Summarise how the measured RQ links the organism’s metabolic pathway to the experimental data. Students complete an exit ticket stating their RQ result and its interpretation. For homework, ask them to design a modification to improve measurement accuracy for the next class.
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