# Core practical - Investigate respiration rate in living organisms

Living organisms take up oxygen from the air and use it for .

We can measure the uptake of oxygen in a given time to work out the rate of respiration.

The equipment used is called a and the effect of changing the temperature on the rate of respiration can be investigated. Respirometers are used to measure the rate of respiration. The diagram shows equipment set up which is being used to measure the respiratory rate of an insect. The higher the rate of respiration, the more the coloured liquid moves. The experiment has a control with no insect in order to compare results.

A wide variety of living organisms can be investigated including insects, woodlice, maggots or germinating peas.

A respirometer

## Method

• The apparatus consists of two tubes, one containing the living organisms and the other with glass beads to act as a control.
• Both tubes contain an alkali such as sodium hydroxide to absorb any carbon dioxide given off during respiration. This ensures that any volume changes measured in the experiment are due to oxygen uptake only.
• Once the apparatus has been set up, the movement of the coloured liquid towards the insect will give a measure of the volume of oxygen taken up by the insect for respiration.
• The reduction of volume in the tube increases pressure causing the coloured liquid to move.
• The distance moved by the liquid in a given time is measured will provide the volume of oxygen taken in by the insect per minute.
• Volume is given by volume of a cylinder $$V = \pi r^2 h$$, where $$h$$ is the distance moved by the coloured liquid. The unit of rate of respiration is cm3/min.

To investigate temperature the experiment is repeated at different temperatures, eg 10, 15, 20, 25, 30°C.

Move on to Video