12.2.14—Respirometer investigations

A respirometer estimates respiration rate indirectly from gas-volume or manometer change over time. For aerobic respiration, oxygen consumption changes the gas volume; the result is a rate only when the change is related to a defined time and matched biological material.

1. Set up experimental and control tubes: place the respiring organisms in one sealed tube and an equal volume of inert material in the control. The control helps compensate for pressure or temperature changes that are not caused by respiration.
2. Control the conditions: place both tubes in a thermostatically controlled water bath. Keep organism type, mass or volume, acclimation time, temperature, seal and run duration matched. Use soda-lime in both tubes when the aim is to absorb carbon dioxide and isolate oxygen-consumption change.
3. Calibrate and reset: record the initial manometer position, allow the apparatus to equilibrate, and reset the fluid/air volume before a new temperature or replicate. Keep the apparatus sealed during the measurement.
4. Measure a rate: record the manometer movement over a known time and convert it to gas-volume change using the validated apparatus geometry; express the result as change per unit time. If a capillary radius and fluid distance are supplied, the volume relationship is (V = πr^2h).
5. Repeat and compare: repeat at each temperature or condition, calculate a representative value, and plot or compare the rates. Interpret the result as an indirect oxygen-consumption measure, not a direct ATP measurement.

A respirometer with soda-lime measures oxygen consumption during aerobic respiration; it does not measure anaerobic respiration directly. A single manometer reading is not a rate, and a change in temperature can affect the apparatus as well as the organisms. Do not invent numerical values, apparatus specifications or unsafe procedures; distinguish this investigation from the separate RQ calculation using paired soda-lime runs.