Biology - Microorganisms and Disease (AQA)
Some pathogens, like bacteria and fungi, can be grown in Petri dishes.

Biology - Microorganisms and Disease (AQA)

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.

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.

How do bacteria and viruses make you feel ill?
They both damage the cells in your body
Bacteria irritate the cells of your body and viruses produce toxins
They take over the cells in your body
The waste materials from bacteria are toxic to the body and viruses damage your cells
Bacteria and viruses work in different ways
Which of the following can be used to help protect your body from microorganisms?
Vaccination and antibiotics
Antibiotics only
Vaccination only
Vaccination prevents infection but antibiotics treat bacterial infections. Antibiotics have no effect on viruses
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?
They didn't know about microorganisms and how they can cause disease
They were too lazy
Hand cleaning gels for hospitals had not been invented
Hospitals could not afford to buy soap for them to use
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
Which of the following is an example of passive immunity?
Mucus and cilia in the respiratory system
Hydrochloric acid in the stomach
Lysozyme (an enzyme) in tears
All three of the above
As well as these examples, there is also the skin which acts a physical barrier
Robert Koch discovered how to grow bacteria in a laboratory. How did this help medical science?
It prevented laboratory technicians from catching infectious diseases
It enabled him to identify some pathogenic microorganisms and linked them to specific diseases
It allowed doctors to make their own vaccines for their patients
It meant that hospitals could now save money on drugs
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
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?
Sterilise the Petri dishes and use sterilised agar gel
Sterilise the wire loops used for sampling in a flame
Seal the Petri dishes with sellotape
Pick up the antibiotic discs using their hands
The best way to handle antibiotic (and disinfectant) discs is using sterilised forceps
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?
It is less dangerous as the bacteria grow more slowly
It is cheaper
School agar gel melts at temperatures above 25oC
Schools and colleges can't leave the heaters on all day and all night
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
Vaccination is used to immunise people against diseases. Pick the false statement:
When a vaccine is injected into the body, it stimulates the white blood cells to produce antibodies against the pathogen
There are no possible side-effects from any vaccination
Vaccines can contain the live pathogen that has been specially treated to make it harmless
Harmless fragments of the pathogen and toxins produced by pathogens can both be used as vaccines
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
Why are antibiotics no good for treating colds and 'flu?
Colds and 'flu are viruses
Colds and 'flu are not viruses
Colds and 'flu are caused by bacteria that are resistant to antibiotics
Antibiotics work too slowly
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
Which of the following statements is not true?
Unless it is controlled, HIV attacks the body's immune cells
HIV can be spread through sexual contact and by drug users who share needles
HIV develops from AIDS
The initial effect of HIV is usually a flu-like illness
AIDS is the late stage of the HIV infection. The body's immune system is so badly damaged that it can no longer deal with other infections
You can find more about this topic by visiting BBC Bitesize - Lifestyle and health

Author:  Kev Woodward

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