There are many different designs of respirometers, though they all have certain features in common
The organisms respire aerobically and absorb oxygen from the air
Repeat readings should be carried out for each set of experimental conditions, in order to identify and eliminate anomalies
Analysis
Use of technology to measure rate of respiration
Oxygen sensors and CO2 monitors can measure oxygen and CO2 concentration in real-time
Dataloggers can record data over a period of time for analysis later
The typical set-up of a respirometer
A respirometer was set up with germinating mung beans in the experimental tube. After a period of equilibration, the liquid in the capillary was measured to move by 2.3 cm in 25 minutes 30 seconds. The capillary tube had an internal diameter of 0.30 mm.Calculate the rate of respiration of the mung beans, measured as the rate oxygen uptake, in mm3 hr-1Use the value of pi (π) = 3.141 and state your final answer to 2 significant figures
Step 1: Calculate the cross-sectional area of the capillary tube
Diameter = 0.30mm, so radius = 0.30 ÷ 2 = 0.15 mm
Cross sectional area = πr2 = 3.141 ✕ 0.152 = 0.0707 mm2Step 2: Calculate the volume of oxygen that had been taken up
The liquid moved 2.3 cm, which is 23mm
Volume of liquid moved in 25 minutes 30 seconds =πr2h , where h = 23 mm
= 0.0707 ✕ 23 = 1.625 mm3
Step 3: Calculate the rate of oxygen consumption per hour
25 minutes 30 seconds = 25.5 minutes
Rate per hour = 1.625 ✕ (60 ÷ 25.5)3.824 mm3 hr-1
To 2 sf = 3.8 mm3 hr-1
Will the animals suffer or feel pain?
There are several ways you can manage variables and increase the reliability of results in respirometer experiments:
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