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Planning an experiment into the effect of mouthwash on bacteria

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A2 Investigation Draft Plan (2010-2011) RESEARCH AND RATIONALE Aims: * To find out the effect of different brands of mouthwashes on microbes. * Comparing the efficiency of a range of anti microbials in mouthwash on the microbes and which works better than the others. Theory: Growth of microbes Bacterial growth is the division of one bacterium into two daughter cells, which are genetically identical to the original cell and refers to the number of cells. There are different factors that influence the growth of microbes and this is due to specific enzymes. Each of these enzymes function best when in the presence of the optimal environmental conditions of temperature, pH, oxygen, redox potential and osmotic pressure and these increase the growth rate of microbes. Microbes obtain almost all their nutrients in solution of surrounding water and in addition, the presence of the listed factors increases this growth. Prevention of growth of microbes The control of microbial growth is important in the prevention of microbe development and is affected in two ways, by killing microorganisms or by inhibiting the growth of microorganisms. The control of the growth usually involves physical or chemical agents, which either kill or prevent the growth and are referred to as static agents. Enzymes and Inhibition In the presence of enzymes, living cells rapidly carry out many biochemical reactions. ...read more.


I am also interested in the way mouthwashes have been used for decades to help in a medicinal way to improve the condition of people's teeth and as it has been used for so long, I would like to see this importance of mouthwash clearly demonstrated with its effects using this investigation. PLANNING Statistics: I have decided to carry out the Mann-Whitney U test as it will tell me whether the medians of the data sets are significantly different from one another as I have unmatched ordinal data and will result in 10 samples of each mouthwash to base my results on. I think that it is the best and most successful way to investigate the effect of different mouthwashes on microbes. Method for investigation: 1) Prepare agar gel using 5 grams of Agar mixed with 500 cm� of water then wait for it to set. 2) Prepare the petri dishes with the bacteria (microcccus liteus) evenly distributed onto it using the spreader. 3) Measure 20 cm� of each mouthwash needed for testing accurately using the small measuring beakers (50 cm�). 4) Test each mouthwash brand with the microbial culture. 5) Prepare 4 pieces of filter paper discs by soaking them in each brand of mouthwash to be tested. ...read more.


11) Make measurements of the microbial culture using digital callipers to help compare the anti-microbial properties of the different substances. 12) Place paper underneath the agar plate to make this easier. Apparatus * Microbial broth culture (microccus liteus and E-coli) * Bunsen Burner * Container to hold water in to heat Agar * Forceps * Water * Petri dishes (20 -A, B, C, D, distilled water) * Small beaker to measure amount of mouthwash used - 50 cm� (1 beaker per mouthwash) * Agar spreader * Filter paper * Pipette * Marker pen Diagram Risk Assessment Risk Minimising Procedure Microbes on clothes Wear laboratory coats Microbe infection spread Close dishes with lids Microbes on skin Wear gloves Microbes in eye area Wear eye protection (goggles) Commercial products (mouthwashes A, B, C and D) Limit contact with skin and keep away from the eye area Spills Wipe down work area with antibacterial liquid Variables * Independent: - concentration of the mouthwashes used * Dependant: - zone of inhibition around paper disc * Controlled: - Amount of microbes used in each sample - Type of microbes used - Volume of mouthwash Sensitivity * Digital callipers - zone of clearing - 0.005 mm Accuracy * Diameter of the microbes to the nearest mm * Amount of mouthwash used to the nearest cm� Results Result No. Mouthwash A Mouthwash B Mouthwash C Mouthwash D 1 2 3 4 5 6 7 8 9 10 ...read more.

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