The Use of Respirometer

Dianne Chabira

Screw tap

Scale (1mm2)

Syringe

Gauze in which organisms are

placedSoda lime

The respirometer can show the:• volume of oxygen that has

been inspired/consumed by an organism

• Volume of carbon dioxide expired/produced by the organism

Maggots

Oxygen consumed

Pressure drops

In right tubeAir moves in from the left tube

x

CO2 expired is absorbed by soda lime, so it does not affect the pressure in the tube

Oxygen consumed

Pressure drops

In right tube

Air moves in from the left tube

CO2 expired is absorbed by soda lime, so it does not affect the pressure in the tube

Liquid/ink moves in the right tube

towards the organisms

x• The distance moved

by the blue ink can be measure from 1mm2 scale placed behind capillary tubing

• The purpose of the syringe: change pressure in the right tube at the beginning so that blue ink is level.

• If the length of the capillary tube is measured, then the cross section area of the tube can be found at any point

• Multiplying this by the movement of ink in mm will result in a volume. E.g. volume of O2 inspired by the small organisms

The respirometer can show the:• volume of oxygen that has

been inspired/consumed by an organism

• Volume of carbon dioxide expired/produced by the organism

• If soda lime is removed from the right tube, and the experiment repeated,

• then CO2 from the maggots will be placed back into the environment

• If the respiratory substrate is a carbohydrate, the ink should not move.

• Volume of O2 consumed = volume of CO2 produced

• Hence, no pressure change in respirometer.

What happens when the respiratory substrate

is NOT carbohydrate, but proteins or fats?

The volume of oxygen consumed/inspired may be larger or smaller than the volume of carbon dioxide produced/expired If so, movement of ink will be either • Down (more CO2 expired than O2 inspired)

• Up, but not as much (more O2 inspired than CO2 expired)

Scenario A: More O2 inspired

• movement of ink UP, but not as much.

• Hence, volume of CO2 produced = x – y

• Liquid is pushed away

To maggotsTo H2O To H2O To maggotsExperiment Control (x soda lime)

X m

m

y m

m

Scenario B: MORE CO2 expired

• movement of ink DOWN, more CO2 produced

• Hence, volume of CO2 produced is

• = x + y (away from the liquid)

To maggotsTo H2O To H2O To maggotsExperiment Control (x soda lime)

X m

m

y m

m

• The respiratory quotient must therefore be used to determine the respiratory substrate.

• Therefore, the carbon dioxide production of a small animal and their respiratory substrate can be measured.