Respirometers

Biology: Cambridge International A Level, topic 12.1.3

Respirometers can be used to investigate the rate of respiration.

A respirometer is used to measure how much oxygen is used up in aerobic respiration by organisms like small insects or germinating seeds.
The organisms are put in an airtight container along with soda lime.
Soda lime absorbs the carbon dioxide the organisms produce.
When the organisms use up oxygen, the coloured liquid moves along the manometer.
This can be repeated to show the effect of temperature or other factors on the rate of aerobic respiration

$Calculating volume$

To calculate the volume of oxygen used, you need to know the diameter of the capillary tube in the manometer.
You can then use the below formula to calculate the volume of oxygen used:
The volume of O₂ = distance coloured liquid moves x πr²
Where "r" is the radius of the capillary tube.
The volume of oxygen used at different temperatures can be used to analyse the effect of temperature on respiration.

To calculate respiratory quotients, two respirometers need to be set up.
One respirometer should not contain soda lime. This means any carbon dioxide produced is not absorbed.
The tube with soda lime (the experimental tube) will show the volume of oxygen consumed as above.
The tube without soda lime (the control tube) can be used to calculate the volume of CO₂ produced. To do this:
Distance fluid moves in the experimental tube - distance fluid moves in the control tube.

To calculate the respiratory quotient, divide the volume of carbon dioxide released by the volume of oxygen released.

Test yourself on Respirometers