= Pea seed respirometry
The University of Oklahoma K20 Center's handout describes three sealed vial-and-pipette <respirometers> in each <temperature> bath: soaked, germinating <peas>; nongerminating <peas> plus inert plastic beads; and beads alone. Displaced <water> establishes equal occupied <volumes>. Absorbent cotton holds <potassium hydroxide>, which removes <carbon dioxide>; nonabsorbent cotton separates it from the <peas>. The source equilibrates the vials before submersion and again before the initial reading. Colored <water> makes the boundary visible in each calibrated pipette. Readers then record positions every five minutes for twenty minutes.<Cell Respiration by the K20 Center>[Cell Respiration, K20 Center handout adapted from AP Biology Lab Manual, pp. 3–4, procedure 1–16: preparation, equilibration and readings]{ref}
\Image[/pea-respirometer-absorber-and-controls.png]
{title=<Pea seed respirometry>: absorber, gas readout and matched controls}
{description=Original schematic of the university handout's vial-and-pipette apparatus. <Carbon dioxide> is removed from the gas; <molecular oxygen> consumption draws the <water> boundary toward the vial. The three sample groups share a bath and matched occupied <volumes>. Geometry, particle counts and boundary position are illustrative; no measured readings are plotted.}
Bath <temperature>, vial position and seal integrity matter. The beads-only <respirometer> detects common <temperature> or atmospheric <pressure> drift; its change is subtracted from each pea reading. Nongerminating <peas> provide a biological comparison, not an assumption of zero <cellular respiration>. A larger corrected uptake slope for germinating <peas> would support greater <molecular oxygen> consumption by that sample under the tested conditions.<Cell Respiration by the K20 Center>[Cell Respiration, pp. 1, 3–4 and 6: living dormant seeds, position/leaks, corrected differences and slope]{ref}
Equal displaced <volumes> help match the gas spaces; they do not establish equal living <mass> or equal developmental state. Comparing uptake per <seed> and uptake per dry <mass> asks different questions. Leaks, incomplete <carbon dioxide> absorption, gas dissolution and changing water-vapour contributions can distort the <respirometer> inference. A blank correction cannot repair a sample-specific leak. These are consequences of the <respirometer gas balance>, rather than measurements reported in the handout.
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