Biology - Microorganisms and Disease (AQA Syllabus A)

One of the topics covered in GCSE Science is the requirements for keeping healthy. This is the third of six quizzes looking at this subject and it concentrates in particular on microorganisms, such as bacteria or fungi, which cause disease.

It's hard to believe but there was a time when doctors who performed operations, examinations and post mortems did not wash their hands at all. The reason was that there was no 'germ theory'. They had no idea of the existence of microorganisms and no idea that some of these were pathogenic (create infectious diseases). Microorganisms are microscopic, living, single-celled organisms such as bacteria. Sometimes people refer to viruses as microorganisms, which they are not. Viruses are not alive, they are simply a strand of DNA in a protein coating.

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The first steps towards the levels of hygiene that we know and use today came in the middle of the 19th Century when a Hungarian doctor, Ignaz Semmelweis, realised that disease was transferred from one patient to another on the hands of doctors. So he instructed his team to wash their hands in between working on different patients. The result was spectacular and immediate - patient deaths dropped dramatically.

There was no understanding of how this worked as the bacteria which cause infections had not been discovered. Because of this his idea was not accepted by other doctors at the time, even though the results were obvious. About 20 years after Semmelweis's discovery, French scientist Louis Pasteur came up with the 'germ theory'. He showed that food went off because of contamination by microorganisms from the air and argued that these could cause disease. His theory backed up what Semmelwies had said many years before and led to the development of antiseptics.

Careful studies of pathogenic microorganisms can be carried out in a laboratory to find the most effective ways of defending against them. This is done using petri dishes partially filled with a nutrient gel. All of the equipment used has to be extremely well sterilised beforehand in order that the results are accurate. Growing microorganisms in a school laboratory could be dangerous so to keep the risks low, the cultures (sealed petri dish plus contents) are kept at temperatures of no higher than 25oC.

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  1. Vaccination is used to immunise people against diseases. Pick the false statement:
    There has been a lot of debate about the vaccine MMR which is used against measles, mumps and rubella as some people say it has harmful side effects
  2. In many hospital wards it is necessary for you to wash your hands with a special gel before going in or out. Before the middle of the 19th Century, not even doctors washed their hands. Why not?
    In the Crimean War (1853-56) 16,000 British soldiers died of illness caught in hospitals and fewer than 3,000 were killed in battle
  3. Which of the following can be used to help protect your body from microorganisms?
    Vaccination prevents infection but antibiotics treat bacterial infections. Antibiotics have no effect on viruses
  4. Why are antibiotics no good for treating colds and 'flu?
    Viruses work by damaging cells from the inside so destroying them would probably do as much damage to the cell as the virus itself. However, doctors do in fact sometimes prescribe antibiotics when people have colds or flu in order to cure secondary infections. Whilst your body's defences are weakened by the virus, it is more likely that bacteria can get past them, making you doubly ill
  5. Robert Koch discovered how to grow bacteria in a laboratory. How did this help medical science?
    He discovered the cause of tuberculosis and cholera. Although he didn't have a cure, he developed methods of containing outbreaks of these two diseases. Modern methods for controlling the spread of infectious diseases are still based on his ideas from the end of the Nineteenth Century
  6. Why are bacteria cultures in a school or college laboratory grown at much lower temperatures (25oC compared to 37oC) than in a professional microbiology lab?
    Pathogenic bacteria grow very efficiently at 37oC (body temperature). It would be dangerous to incubate (keep and grow) cultures at temperatures close to body temperature (37°C) in schools and colleges because doing so might allow the growth of large colonies of harmful pathogens
  7. How do bacteria and viruses make you feel ill?
    Bacteria and viruses work in different ways
  8. Which of the following is an example of passive immunity?
    As well as these examples, there is also the skin which acts a physical barrier
  9. A group of Y11 students carried out an investigation into antibiotics which required them to grow some bacteria cultures. Which one of the following is not something they would have done whilst setting up the cultures?
    The best way to handle antibiotic (and disinfectant) discs is using sterilised forceps
  10. When you catch a bad cold at the start of winter, quite often, the next few colds are not as bad. Which of the following options could be a reason for this?
    Each time a pathogen makes you ill, your body develops defences against it. Unfortunately, cold and influenza viruses gradually change (mutate) and so it is possible to catch a cold (or flu) again a few weeks later. It isn't as bad because the antibodies can still defend you. The longer you go between colds, the more the virus will change and the less your body will be able to defend itself

Author: Kev Woodward

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