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Branded Bleach is more effective at killing E. coli than Non branded bleach - An investigation

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Is branded bleach more effective at killing E.coli than a non branded version? Contents Page Number 1. Hypothesis 1 2. Introduction 1 - 3 3. Plan 4 - 13 4. Results 14 5. Analysis 15 - 17 6. Evaluation 17 - 20 7. References/Bibliography 20 Appendices Attached Hypothesis Branded bleach, Domestos, will kill more bacteria than Non-branded Somerfield thick bleach. This will be shown by the larger zones of inhibition around branded bleach. Null Hypothesis There will be no significant difference between the zones of inhibition for each bleach. Introduction Both brands of bleach contain ingredients which are active in the death of the bacterium Escherichia coli, shown below. As a bacterial cell it is classified as prokaryotic which differs to eukaryotic cells found in humans; which means the cell's nuclear material is not bound by a nuclear envelope, prokaryotic cells also have fewer organelles and the volume/size of a prokaryotic cell is up to 10,000 times smaller. E.coli is a rod shaped Gram negative bacteria. Using the binomial naming system Escherichia coli is named with the genus of the bacterium first followed by the species, abbreviate to E.coli. Also bacteria named in this way are always written in italics. Further classification of the bacteria based on the cell wall can predict how the active ingredients of the bleach will affect the bacteria. Classifying the cell wall can be done by the Gram stain method. Firstly in this method a bacterial smear is heat fixed to a microscope slide, then flooding with crystal violet and washed with Gram's iodine. Next decolourise the slide with alcohol. The two distinctions of bacteria are Gram positive and Gram negative. Gram positive bacteria will stay purple after flooded with a safranin counter stain, whilst gram negative bacteria turn red. The results of the Gram stain test are based on the structure of the cell wall. Cell wall's of Gram positive bacteria are rigid and made of peptidoglycan murein. ...read more.


Simplest method of quick and easy fire Permanent marker pen For writing on Petri dishes Easily writes on Petri dishes Methylated Spirits Used to be burned on glass rod eliminating any possible contaminates Obvious choice for a flammable substance Matches/Lighter Source of ignition for Bunsen Easy source of ignition Fifteen nutrient agar Petri dishes Location of bacterial growth with sufficient nutritional content. Obvious choice for safe observable bacterial growth. Acetate sheets For sketching the areas of the zones of inhibition Transparent Micropipette Measuring out very small quantities of the bacterium Measures to a very small level E.coli bacteria For growing and effectively killing using bleach A well known bacteria found in kitchens and toilets where bleach is commonly used. Forceps Handling paper discs Can survive the impact of flame as they're metal whilst killing possible contaminates Pipette tips For attaching to the micropipette for extraction of bacteria Can be easily disposed of in disinfectant Three 10cm�Graduated pipettes For both brands of bleach and sterilised water An accurate way to measure up the correct measurements for each bleach solution Sterilised water Used for diluting bleach solutions A neutral compound that works well to form a solution Domestos bleach Used as the branded bleach Contains the active ingredients: sodium hypochlorite and anionic surfactants Somerfield thick bleach Used as the non - branded bleach Contains anionic surfactants and sodium hydroxide Apron To protect clothing and skin from bleach and E.coli contamination Disposable Tape To secure the Petri dish closed Obvious and easy mechanism of sealing the dish. Anti-bacterial hand wash To wash contaminates of hands Cheap, convenient and obvious Paper towels To mop up spillages Very absorbent 2 50ml beakers As a vessel in which to mix the bleach Simple mixing mechanism Glass rod (right angled) To spread E.coli in the Petri dish Rod can be kept aseptic using methylated spirits and the Bunsen burner. Thermostatic incubator To keep a constant temperature of 25�C when growing the bacteria. ...read more.


The minimum measurement made using the graduated pipette was 2.5cm�of bleach and if the systematic error of the instrument is 0.06 then the percentage error of the maximum measurement is, (0.06/2.5) x 100, 2.4%. So the reading could have differed by a maximum of 2.4% of what was calculated. Improvements to the experiment Source of error Improvement to avoid error Justification of improvement 1) The bacterial growth cycle being in different stages of the bacterial growth cycle Use the same bacterial population in a short time period Bacteria should be in the log phase preventing any unexpected results due to this 2) Volume of bleach on paper discs Immerse the paper discs in the bleach for a set time using a stop clock. The exact same of product should be present in each Petri disc. 3) Counting squares as a method of calculating the zone of inhibition More accurate graph paper could be used Half squares can be easily valued 4) Possibility of a differing E.coli concentration Shake the vial of E. coli The concentration will become equal 5) Differences in nutritional content of agar When making the agar ensure an even ratio of ingredients and ensure that it settles evenly. Should provide the same nutrients for all the bacteria so their growth should be fairly even. If the nutrient agar begins to run out than it becomes a significant limiting factor causing the bacteria to enter the stationary phase as the number of bacteria dying is equal to the new growing. Experimental validity Overall the experiment contains an overwhelming number of anomalies which could have resulted in a completely different conclusion. This can be expressed graphically especially by the complete lack of a normal distribution in the histogram, further supported by the T test. As the critical value required proving the validity of the hypothesis was 64 and the obtained result was 68 the experiment was quite close to proving the hypothesis. For the experiment to be much more sufficient the experiment needs to be repeated with many more samples of data. ...read more.

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