COAS Biology 1 Teacher Resources Original material © Cambridge University Press 2008 1
4 Practical 3
Measuring vital capacity
Safety
The tubing should be sterilised by washing in a suitable disinfectant such as 5% bleach solution, followed by two washes in distilled water.
Apparatus and materials
• large calibrated bell jar (at least 5dm3) or modified plastic container (see diagram) with a sealable opening at the top / • length of wide-bore tubing, e.g.corrugated spirometer tubing• bung to fit tubing
• large bucket or deep sink able to contain the bell jar / • disinfectant for tubing
Introduction
Vital capacity can be measured by collecting a forced exhalation over water in a large bell jar or modified plastic container. Either vessel is first calibrated by pouring in measured volumes of water and marking a scale in dm3 on the outside, using a permanent marker.
Procedure
1 Immerse the bell jar or plastic container in a large bucket or deep sink three-quarters full with water. The jar or container should have the bung or cap removed, so that it fills with water. Place a wide-bore tube into the jar from below.
2 Adjust the position of the bell jar or container until the water level is at the zero mark, then place a bung in the top of the jar, or screw a cap on the spout of the plastic container.
3 Ask a student subject, wearing a nose clip, to inhale as deeply as possible and breathe out as much air as they can through the tubing. As the subject exhales, lift the bell jar or container out of the water, trying to keep the levels inside and out the same.
4 When the subject has finished breathing out, insert a bung in the end of the tubing.
5 Make sure that the level of water inside the bell jar or container is the same as that outside. Record the volume of air inside, which is the subject’s vital capacity.
6 Disinfect the tubing and repeat steps 1–5 with other members of the class.
7 Collect enough measurements so that you can plot a frequency distribution histogram of the vital capacities: a minimum sample size of about 20 individuals of the same sex is needed. You may need to measure vital capacities in another class to achieve a big enough sample size.
8 The normal distribution of vital capacities for boys and girls is different. If possible, investigate this by collecting suitable data and plotting two frequency histograms.
COAS Biology 1 Teacher Resources Original material © Cambridge University Press 2008 1