• 10 cm industrial methylated spirits
• Pipette (sterile)
• Paper discs (e.g. Whatman antibiotic assay paper discs)
• Sterile Petri dish
• Sterile forceps
• Tape
• Marker pen
• Incubator set at 25 °C
Method
- To make the plant extract, crush 3g of either garlic or mint with 10cm3 of ethanol
- Pipette 0.1cm3 of extract onto sterile paper disc
- Allow this to dry on the sterile Petri dish
- Meanwhile label agar plates with date and split into four sections. Then put a disc into each section of the agar plate, close and tape with hazard tape.
- Leave this for at least 24 hours
- Observe zone of inhibition and measure with ruler.
Risk Assessment
Likelihood and Severity is on a scale of 1-5, one being low, five being high. Risk is calculated by multiplying likelihood and severity, so is out of 25. Generally, if the risk is over 10 then the experiment should not take place.
Validity
The results will be valid because the experiment is designed to test the hypothesis, so the experiment will test what it is intended to. The results will be reliable as there will be 6 repetitions of this experiment by different groups. The results should be accurate as the equipment is all functioning correctly currently.
Results
The table above shows the results for our investigation into the antibacterial properties of mint and garlic, and the results seem to follow a general trend.
Conclusion
The patterns in the results is that generally the results support the hypothesis which is that the more schlerenchyma fibres that are used, the larger the mass that can be held.
However, there are a few possible anomalies, using the graph I can see that Group 1’s result for 4 and 5 strands is particularly different to the other sets of results as it does not follow the general trend stated in the hypothesis. This measurement was 460g whereas the other groups varied around the 300 mark. It is also the case that the next measurement is significantly lower than other groups results for 5 strands, so this could be another factor in the way that it does not follow the general trend. This could be because the four strands had particularly strong fibres. Group 3’s results as a whole were significantly lower than others. This is most likely due to a systematic error.
Evaluation
During the experiment, I think that many systematic and random errors took place.
Firstly, a systematic error was that as mass was added to the celery fibre’s, the celery could sometimes slip out of its holder, without snapping. This could be mistaken for snapping, so could be used as a result. I suspect this could be why group 3’s results were so low. If I was to do this again I would try and use a tighter clip so as to hold the celery in place, without slipping.
Next, during the extraction of the celery fibres, sometimes skin was used instead of the fibres as they are hard to distinguish between. Obviously using skin would render the results invalid, as it was not testing the hypothesis as the wrong thing was used. Also the skin is likely to be much weaker than the fibres. I think that next time I would cut the celery in half so that the inner fibres can be extracted more easily.
Different people extracting the celery fibres may also have an effect on the outcome as fibres of different sizes and thickness may be acceptable to some, but not others. Next time I would have the same person extracting all the fibres, to minimise differences in the results.
Some people lowered the mass onto the celery fibres, wheras others almost dropped the mass on. Obviously this can have an impact on the strength of the mass, and how long the fibre lasts. If I was to conduct the experiment again, I would get everyone to do the same thing, lower the weight down.
A random error that may have taken place could have been that a particularly strong or weak fibre was used.
I think that the results were valid, as they tested the hypothesis. I also think that the results are relatively reliable, due to the 6 repetitions, however I think that the results were quite inaccurate due to the many systematic and random errors that took place due to the method and the apparatus.
