O-Level Biology Respiration Respirometry Guide
Download printable cheat-sheet (CC-BY 4.0)05 Nov 2025, 00:00 Z
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Respiration investigations let examiners probe both MMO technique (gas measurement, temperature control) and ACE reasoning (aerobic vs anaerobic outcomes).
Practise the classic yeast-glucose setup alongside germinating-bean respirometers, and rehearse how to justify controls, indicator choices, and leak checks in your written responses.
1 | Where this fits in the syllabus
- Section 4 of the SEAB syllabus covers respiration, including aerobic and anaerobic pathways and gaseous exchange (SEAB 2026 syllabus, PDF).
- Paper 3 tasks typically assess:
- Planning: selecting appropriate temperature (30–37 °C for yeast), specifying equal masses/volumes, defining the variable measured (gas volume or indicator colour change).
- MMO: assembling airtight apparatus, timing intervals, reading gas syringes or measuring cylinder meniscus accurately.
- PDO: recording cumulative gas volume, pH/indicator colour scoring, and plotting rate graphs.
- ACE: explaining differences between treatments (e.g. live vs boiled seeds), linking CO₂ production to respiration rate, and evaluating experimental limitations.
2 | Core apparatus sets to master
| Set-up | Key components | Purpose |
| Yeast-glucose respirometer | Conical flask with glucose + yeast suspension, delivery tube into an inverted measuring cylinder or gas syringe, water bath. | Captures CO₂ from anaerobic respiration (if sealed) or aerobic respiration (if air inlet provided). |
| Germinating vs boiled seed setup | Two identical respirometers connected to manometers or gas syringes, each with seeds, cotton wool, and a potassium hydroxide trap. | Compares oxygen uptake; the alkaline trap absorbs CO₂ so volume change reflects oxygen consumption only. |
