Respirometer – oxygen uptake of germinating seeds
BiologyPlant PhysiologyAges 16–17
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Sign in to playThree respirometer tubes in a water bath: germinating seeds, dry seeds plus glass beads, and glass beads only (thermobarometer), each with KOH to absorb CO₂. Change the seeds (peas or maize), their number, the bath temperature (10–35 °C) and the run time; a time-lapse clock records the position of the coloured drop in each capillary every 5 minutes, corrects it using the beads tube, plots O₂ uptake against time, finds the rate from the slope and works out Q₁₀ between two temperatures. Remove the KOH or skip equilibration to see why both are needed.
Lesson: Cellular respiration: measuring O₂ uptake with a respirometer
What it shows
Germinating seeds respire fast: they break down stored starch to release energy for the growing embryo, taking in O₂ and giving out CO₂. In a respirometer the seeds sit in a sealed tube above KOH, which absorbs the CO₂, so the gas volume falls as O₂ is used and a coloured drop moves along a graduated capillary. A tube of glass beads (thermobarometer) records changes caused only by temperature and air pressure, and dry seeds act as a control. The slope of corrected O₂ uptake against time gives the rate of respiration.
How to use
Choose the Seeds, Seeds per tube, Water bath temperature and Run time, then press Start. Readings are recorded every 5 minutes. Tap a tube to zoom in on its scale. When a run ends, change one factor and press Run again to compare. Try the CO₂ absorber and Before readings menus.
Parameters you can change
- Water bath temperature 10–35 °C
- Seeds Peas, Maize (corn)
- Seeds per tube 5–40 seeds
- Run time 10–60 min
- CO₂ absorber KOH, No KOH (water instead)
- Before readings Equilibrate 10 min, clip open, Close clip, start now
Questions to explore
- Why does the coloured drop hardly move when the KOH is removed, even though the seeds are still respiring?
- Why must the glass-bead tube contain the same volume as the seed tubes?
- How many times faster is O₂ uptake at 25 °C than at 15 °C, and what does that tell you about Q₁₀?
