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A2 Biology Coursework -Investigation into the effect of different concentrations of antibiotics on the growth of bacteria

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Biology Coursework Aim: My aim is to investigate the effect of different concentrations of antibiotics on the growth of bacteria. Hypothesis: I predict that as the concentration of the antibiotics increases the bacteria growth decreases Null Hypothesis There is no link between the concentration of antibiotics and the effects it has on the growth of the bacteria Theory Antibiotics work in 4 ways, which are listed below: 1. Cell Membrane Disruption - This involves making the cell fully permeable which results in substances moving into it causing it to burst and so kills the bacteria 2. Inhibiting Nucleic Acid Synthesis - This method doesn't kill the bacteria off but keeps the growth level static. The bacteria isn't able to replicate its DNA and so no binary fission occurs, causing the growth level to become static 3. Inhibiting Cell Wall Synthesis - This is where an antibiotic inhibits the enzyme required to form cross links within the cell wall and as a result the bacteria looses its structure and is unable to function properly . 4. Inhibiting mRNA Translation - This is where the Translation part of protein synthesis is inhibited by binding across the bacterial ribosome meaning proteins and enzymes the bacteria it requires isn't made and so dies. Having said how antibiotics work above, it is logical to presume that the higher the concentration of antibiotics the more effective it will be in wiping out, and killing the bacteria. Because the more antibiotic molecules there is in the solution means there is a higher chance that these antibiotic molecules will come upon a bacterial cell and disrupt the cell and kill it . So in conclusion it is logical to state that the higher the concentration of antibiotic the more effective the antibiotic will be at killing of the bacteria. Dependant Variable There are a number of different ways of measuring the effectiveness of the antibiotics but I will be using the technique of bioassays. ...read more.


Do the experiment again but this time substitute the antibiotic with distilled water. Precautions The precautions I will be taking are: * Clean the work surfaces with disinfectant to prevent contamination * Do not eat or chew in the lab * Wear the necessary safety gear * Turn the Bunsen burner flame to yellow when not in use * Use scissors to cut the cell o tape rather than mouth to prevent contamination * When opening the lids of the gar solution, Petri dishes etc I will try to keep the opening to minimum to prevent airborne contamination * Flame the bottle necks to prevent contamination by killing the bacteria * Use a separate syringe for each use- prevent cross contamination * I am going to dip the glass rod in ethanol to kill bacteria * I am going to place corks on test-tubes to prevent airborne contamination * Use buffer solution to keep pH level constant to prevent ph becoming a variable * Label all test tubes and Petri dishes- to prevent mixtures * Cello tape the Petri dishes so that the lid is secure but to allow oxygen to enter Table Test tube Percentage Concentration (%) Width of clear zone (mm) Average Diameter (mm) EX1 EX2 EX3 1 100 2 90 3 80 4 70 5 60 6 50 7 40 8 30 9 20 10 10 11 0 Graph Implementation Apparatus 1. Agar Solution 2. Bacteria Culture 3. Antibiotic Solution 4. Distilled sterile Water 5. Petri Dish 6. Bunsen Burner 7. Syringe 8. Scissors 9. Glass Rod Method 1. Firstly I got a lab coat and wore it as a safety measure and also used disinfectant to disinfectant the table I was carrying my experiment out on to rid the area of any bacteria to limit the chances of any contamination 2. I then used hand wash to wash my hands 3. ...read more.


* Also the cotton wools placed in the test tubes to prevent oxygen from entering was a slightly different size and may not have totally prevented the air entering into the tube meaning that if it was bigger the would have been a higher chance that less oxygen may have entered, decreasing the bacteria's ability to grow much faster. De to the wool being smaller in size, more oxygen may have entered meaning that more bacteria were growing faster which means that the absorbency reading will be higher, this may be the cause of my anomalous results. * The amount of each solution had to be the same cause if they weren't then this would have affected the growth and death of bacteria because if more antibiotic solution was present then more bacteria would have died resulting in a decrease in light absorbency and vice versa with the bacterial solution. * Also the light absorbency of all the test tubes differed as they could not all be measured in one go meaning that in some test tubes some bacteria had more time to grow, giving an invalid absorbency reading. The method I used could have been improved since I used turbidamitry which gives total cell count, both living and dead isn't really accurate or representative. I could have improved this by using bioassays which is a method that will only count the living cells which may have given a better representation. I could also improve the experiment next time by making sure that the size of the cotton wool was decent sized so that it has a higher chance of preventing oxygen entering into the test tube allowing the bacteria to grow more faster. Another way to improve the experiment is to make sure to properly rinse out the cuvettes after each sample from each test tube was measured in the colorimeter to prevent contamination and an invalid light absorbency reading. ?? ?? ?? ?? Kamrul Hassan ...read more.

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Here's what a teacher thought of this essay

4 star(s)

Excellent planning with detailed method and control of variables. Analysis of results, interpretation of statistical test and evaluation are weaker.

Marked by teacher Adrian Fisk 14/03/2013

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