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Difficulty: EasyAnalyzing Experimental Procedures and Apparatus

A student constructs a respirometer apparatus to measure the rate of cellular respiration (O2O_2 consumption) in germinating seeds. Match each component of the apparatus to its primary experimental function in the setup.

  • Potassium hydroxide (KOH) pellets placed at the bottom of the respiration chamberAbsorbs CO2CO_2 produced by respiration so volume changes reflect only O2O_2 consumption
  • Colored fluid droplet inside the horizontal graduated pipetteMoves inward to indicate the volume of O2O_2 gas consumed over time
  • Glass beads in an identical secondary chamber (control chamber)Controls for gas volume changes caused by changes in ambient temperature and pressure
  • Water bath surrounding both respiration chambersMaintains a stable temperature around the chambers to minimize thermal expansion of gas

Answer

The correct pairings match each component to its functional role in measuring respiration: Potassium hydroxide (KOH) pellets absorb carbon dioxide gas; the colored fluid droplet measures net oxygen volume consumed; glass beads serve as a thermobarometric control for temperature and pressure changes; and the surrounding water bath stabilizes the experimental temperature.
Potassium hydroxide (KOH) functions to remove CO2CO_2 gas from the chamber so that net volume change corresponds strictly to O2O_2 uptake. The colored fluid droplet in the graduated tube provides a direct reading of this volume change as it shifts inward. Glass beads act as an inert thermobarometric control to correct for ambient pressure and temperature fluctuations, while the surrounding water bath stabilizes temperature throughout the experiment.

Step-by-Step Solution

1
Analyze the chemical byproduct removal in the respiration chamber.
Germinating seeds consume O2O_2 and produce CO2CO_2 in equal molar ratios during aerobic respiration. KOH absorbs CO2CO_2, isolating O2O_2 consumption as the sole cause of pressure drop.
Without removing CO2CO_2, gas production would offset gas consumption, resulting in no measurable change in net gas volume.
2
Analyze how volume change is quantified.
The movement of the colored fluid droplet in the attached narrow pipette directly registers the decrease in gas volume.
The fluid marker provides a visual and quantifiable reading of volumetric rate over time.
3
Evaluate experimental controls for environmental variables.
Glass beads provide non-living, equal-volume displacement to isolate biological respiration from external atmospheric changes, while the water bath maintains a constant temperature environment.
Gas volume is sensitive to temperature and pressure changes (PV=nRTPV = nRT); controlling these variables ensures validity.

Key Concept

Function of components in a respirometer apparatus
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Topics

Analyzing Experimental Procedures and Apparatus

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