Respirometer

A simple whole plant respirometer designed to measure oxygen uptake or CO₂ release consists of a sealed container with the living specimen together with a substance to absorb the carbon dioxide given off during respiration, such as soda lime pellets or cotton wads soaked with potassium hydroxide. The oxygen uptake is detected by manometry. Typically, a U-tube manometer is used, which directly shows the pressure difference between the container and the atmosphere. As an organism takes up O₂, it generates a proportionate quantity of CO₂ (see respiratory quotient), but all the CO₂ is absorbed by the soda lime. Therefore, all of the drop of pressure in the chamber can be attributed to the drop of O₂ partial pressure in the container. The rate of change gives a direct and reasonably accurate reading for the organism's rate of respiration.

As changes in temperature or pressure can also affect the displacement of the manometric fluid, a second respirometer identical to the first except with a dead specimen (or something with the same mass as the specimen in place of the organism) is sometimes set up. Subtracting the displacement of the second respirometer from the first allows for control of these factors.

The set up of modern respirometers is described in more detail under respirometry. A respirometer may also be called an oxygraph. Suppliers for whole animal respirometers are e.g. Sable Systems, Respirometer Systems and Applications, Qubit Systems, Eco-environment, Bio-technology, or Challenge Technology; for mitochondrial respirometers, Oroboros Instruments, Hansatech Instruments, or YSI.