Investigate the effect of different preservatives on frozen peas. Establish that decay is caused by the action of microbes, and therefore preservatives work by reducing microbe activity.

Each group could prepare a tube with a different preservative. Or you could set up all the tubes in advance to demonstrate the different effects.

Test-tube rack, 1
Test tubes, 8
Non-absorbent cotton wool plugs, 8
Marker pen
Frozen peas, 24
Distilled water
Solutions of different preservatives, 5 cm3 of each
Enough of the following solutions for 5 cm3 per experimental set: * sodium chloride solution (dilute) (Note 2) * sodium chloride solution (concentrated)
(Note 3) * sugar solution (sucrose) (Note 4) * vinegar (clear white table vinegar) (Note 5) * sodium nitrite/ sodium nitrate (III) (NaNO2) (Note 6)

Carry out a full risk assessment before planning any work in microbiology (see note 1 for details).
Food or drink should not be stored or consumed in a laboratory that is used for microbiology.
Take care with vinegar and sodium nitrite solutions. Avoid contact with eyes and wash hands after handling.
Leave the cotton wool plugs in when observing the peas next lesson.
Do not eat the peas!
Read our standard health & safety guidance
1 Before embarking on any practical microbiological investigation carry out a full risk assessment. For detailed safety information on the use of micro-organisms in schools and colleges, refer to Basic Practical Microbiology – A Manual (BPM) which is available free from the Society for General Microbiology (email education@sgm.ac.uk) or go to the safety area of the SGM websitehttp://www.microbiologyonline.org.uk/teachers/safety-information, or refer to the CLEAPSS Laboratory Handbook, section 15.
2 Sodium chloride solution (dilute) is 1% w/v (See CLEAPSS Hazcard: Sodium chloride is described as 'LOW HAZARD’)
3