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To find which Antibacterial Substance best Inhibits the Growth of Bacteria.

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BIOLOGY COURSEWORK ANTIBACTERIAL SUBSTANCES Aim: To find which Antibacterial Substance best Inhibits the Growth of Bacteria. PLAN Introduction: The word antibiotic means 'against life'. An antibiotic is a chemical compound that is used to kill or stop the growth of infectious organisms. Antibiotics are of a 'selective toxicity' because they harm the invading organism not the host. Antibiotics only kill bacteria and do not affect viruses. There are 4 groups of antibiotics: Penicillin Cephalosporins Tetracycline Erythromycins The different types of antibiotics act against a wide range of bacteria. Penicillin is a narrow-spectrum antibiotic - they only destroy a limited number of species of antibiotics, but Tetracycline is a broad-spectrum antibiotic which acts against a broad variety of bacteria. Bacteria can become immune and resist antibiotics, so new ones have to be constantly found. Sometimes a gene in the bacteria will spontaneously change, so the antibiotic does not recognise it and the bacteria can resist the effect of the antibiotic. This is called a Mutation. Bacteria can also become immune to antibiotics by other bacteria transferring genetic material. This often enables the bacteria to acquire resistance to more than one type of antibiotics. Sir Alexander Fleming- (1881 - 1955) was a famous biologist who discovered that some bacterial cultures were contaminated with mould. ...read more.


7. 2.5ml of the bacteria Bacillus Subtilus, which is in a suspension form, will have to be poured onto 10ml of autoclaved water in the agar plate. This will be done using an aseptic technique. One hand will hold the bottle, the other needs to open the agar plate. The lid of this bottle with have to be opened with the little finger of one hand, whilst the other hand opens the agar plate slightly and the bacteria is poured in with one swift action. 8. Make sure the bacteria is spread over the agar plate evenly by using a glass spreader or inoculation loop. All equipment used should be flamed in a Bunsen Burner to eradicate any micro-organisms. 9. Make sure this is done for all 4 agar plates. 10. After the discs have been soaked for 20 minutes they need to be transferred to the agar plates. 11. Transfer 4 discs from each disinfectant and distilled water to the agar plates by using tweezers. Before transferring each disc, the tweezers should be heated in a bunsen burner. 12. Selotape each agar plate in four corners. Do not selotape all around the agar plate as anaerobic respiration will take place and harmful toxins may be produced. ...read more.


However I did get a few anomalous results. For example when looking at Clearasil, at the fourth disc on days 4 and 5, the clear zone was 3mm on day 4 and then went up to 4mm on day 5. This was an inaccurate result and could have been due to human error of not measuring accurately or it could have been due to too much Clearasil being in one place. If I were to redo this experiment and make it more accurate I would: * Repeat the experiment more times to obtain more results. I would do 12 discs for each antibacterial substance instead of 4 on 3 agar plates. * I would test more antibacterial substances to obtain a better analysis of why some substances kill or remove bacteria better then others. * I could test the rate the bacteria reproduces to see what conditions bacteria work best in. * I could leave the antibacterial substances in for longer than 5 days to see how time has an effect on bacteria. * I could put the agar place in different temperatures or light intensities to see where this has an effect on the bacteria or antibacterial substances. The evidence is quite reliable but I believe that with better aseptic techniques and the spreading of bacteria on the agar plate more evenly the experiment could have gone better. By Serina Ramkhelawon ...read more.

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