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Investigation for the effect of disinfection on bacterial growth

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Investigating the effect of disinfectant on bacterial growth: There are various ways on destroying micro organisms. Antiseptics, disinfectants, heat sterilisation, heat treatment, radiation and antibiotics are all ways of killings micro organisms outside the body. I am going to investigate the effect of disinfectant on bacterial growth. The definition of a disinfectant is a chemical that kills micro organisms. There are many different types of disinfectant; Milton's, tcp, dettol, demestos, alcohol and bleach. I am going to investigate the effect of one particular disinfectant. Ethanol. Ethanol is used in medical wipes and as an antiseptic. Ethanol kills organisms by denaturing their proteins and dissolving their lipids (fats). These fats are found in the cell membrane. Bacteria are small, single cell organisms that are big enough to be seen under the light of a microscope. There are many different types and can be located almost anywhere. A bacteria cells consists of a cell membrane, inside this membrane is a fluid called cytoplasm. At the centre of the cell is a string of DNA. Attached to the cell are sometimes flagella, these help the cell to move. Bacteria divide by mitosis; bacteria can roughly double their population in just 20 minutes. This leads to colonies forming and these colonies are visible. These visible colonies are the things I will be counting. The bacteria I am going to use is E coli (Escherichia coli). A common type of bacteria, which normally lives in the body in your intestines where it helps your body break down and digest food. ...read more.


11-13 Either pair up, or move slowly but accurately The inoculating loop took longer to cool that expected so when I did this experiment there was a slight "pop" or "fizz" when the loop came in contact with the solution, thus killing some of the microbes. 11+13 Wait 45 seconds for the loop to cool. To ensure that it isn't contaminated whilst cooling place the loop near the flame but not actually in. Swiping the zigzag along the surface of the agar jelly when the lid of the agar jelly was low down it was possible to cut the jelly. 13 Take care when streaking the solution across the jelly so as not to cut the jelly. Contamination. Most steps The only way to over-come this is with accuracy and care. My results from this experiment after 3 days were: Concentration % Trial Number Result (colonies) 70 1 0 2 0 60 1 0 2 0 50 1 0 2 0 40 1 2 2 4 30 1 21 2 12 I can see from these results that these are not suffice to conclude my experiment. I have therefore decided to increase the time in which I record my results to 4 days and add one more concentration on to my list to make up the whole 11 agar plates. I will also take into mind the problems with my original method and repeat my experiment. Obtaining Evidence Concentration % Trial Number Result (number of colonies) Average Number of colonies 0 1 126 126 30 1 23 20 2 17 40 1 4* 3 2 2 50 1 1 0.5=1** 2 ...read more.


Microbes are incredibly small as I have already said (the E coli bacterium is approx. 3 microns), which means there is a huge room for error. When looking at my results I can safely say that I have produced results that are useful to my initial title and prediction. My prediction was As the concentration increases the number of colonies formed will decrease. I can say this was decreased by the fact that the graph has a negative gradient (meaning it slopes downwards) and this can be supported by the table which shows the numbers decreasing in these two columns. My prediction has thus been proved. I could of improved my results by measuring to another degree of accuracy such as mm� covered etc. I could of measured my colonies differently. I chose to just count them, whereas I could of drawn four streaks and counted the colonies on the forth streak or draw a shape calculated the area covered by the microbes. Any of these ways would have been ways of counting the number of colonies. These are not necessarily more accurate than the way I have chosen. Possibly the microbes on the final streak might have been more accurate. It would be interesting to find out if it was or not. In conclusion I can say that judging my situation (i.e. a school laboratory) that my results have produced suitable results for my experiment. Naturally there are ways I could have improved my method, apparatus and results I have taken these into account and shall remember them if I decide to repeat my experiment in the future. Francesca Tate 10D Mrs. Dolan 1 ...read more.

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