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Molecular biology What is a respirometer and how is it used? Respirometers are used to measure the rate of respiration of invertebrates or germinating seeds by measuring the rate of oxygen consumption.
syringe tap (closed during experiment) calibrated scale mesh container woodlice or other small invertebrates
filter paper (in both tubes)
Tube A
manometer (capillary U-tube container coloured liquid)
potassium hydroxide or other alkali that absorbs carbon dioxide (in both tubes)
Tube B
Figure 2.34 A simple respirometer
Worked example 2.1
a What was the respiration rate of the germinating
peas? To calculate a respiration rate you must divide the oxygen consumption by the time that the readings were made. In this case the y-axis shows that 3 ml oxygen were consumed in the 20 minute period shown on the x-axis. Thus the respiration rate is 3/20 = 0.15ml min−1 b Why were measurements for glass beads also
Germinating Peas: Oxygen Consumption (Readings) 10 9 8 7 6 5 4 3 2 1 0
Manometer reading/ml
The graph shows the readings taken from three respirometers containing germinating peas, dry peas and glass beads over a 20 minute period.
0
5
Germinating Peas
10 Minutes Dry Pea Seeds
15
20 Beads only
Figure 2.35
taken? The beads act as a control to show that changes in the respirometer readings are due to the peas and not the apparatus itself. c Explain the difference between the readings for dry and germinating peas.
Dry peas did not cause any change in the respirometer reading so they are not removing oxygen from it. This indicates that they are not respiring. Only the germinating peas are using oxygen and so we can say that they are respiring.
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