Pathogens and disease
- Pathogens cause infectious diseases
- Pathogens are tiny microorganisms - usually bacteria or viruses
- When bacteria or viruses enter the body they reproduce rapidly. They can make you feel ill by producing toxins
- Viruses are much smaller than bacteria and reproduce inside cells. The damage to the cells also makes you ill
- Before bacteria and viruses had been discovered, a doctor called Semmelweis realised that infection could be transferred from person to person in a hospital - infected people are said to be infectious
- Semmelweis told his staff to wash their hands between treating patients. However, other doctors did not take him seriously. We now know that he was right
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- Pathogens can be transmitted from one person to another by droplet infection or direct contact. When you cough or sneeze pathogens are sprayed into the air in drops of water
- The skin prevents pathogens getting into the body
- Pathogens are also trapped by mucus and killed by stomach acid
White blood cells are part of the immune system. They do three things to defend the body:
- They can ingest pathogens. This means they digest and destroy them
- They produce antibodies to help destroy particular pathogens
- They produce antitoxins to counteract the toxins that pathogens produce
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Using drugs to treat disease
- Antibiotics kill infective bacteria in the body
- Penicillin is an antibiotic, but there are many others. It was first discovered by Alexander Fleming in 1928.
- Viruses are difficult to kill because they reproduce inside the body cells so any treatment could also damage the body cells.
- Painkillers and other drugs relieve the symptoms of a disease but do not kill the pathogen.
- Your immune system will usually overcome the viral pathogens
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Growing and Investigating Bacteria
- Pure cultures on fon-pathogenic (safe) bacteria can be used for laboratory investigations
- A culture of microorganisms can be used to find the effect of antibiotics on bacteria
- Investigations need uncontaminated cultures of microorganisms. Strict health and safety procedures are used to protect yourself and others.
- Contamination might come from your skin, the air, the soil or the water around you.
- If the culture is contaminated other bacteria could grow, including pathogens.
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To culture (grow) microorganisms in a laboratory you must:
- Give them a liquid or gel containing nutrients - a culture medium. It contains carbohydrate as an enrgy source, various minerals and sometimes other chemicals. A culture medium called agar jelly is used.
- Provide warmth and oxygen.
- Keep them incubated at 25°C in school laboratories and at 35°C in industry.
To keep the culture pure you must:
- Kill all the bacteria on the equipment - pass metal loops through a flame; boil solutions and agar
- Prevent microorganisms from the air getting into the equipment.
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- Dead or inactive forms of a pathogen are used to make a vaccine. Vaccines can be injected into the body
- The white blood cells react by produce antibodies
- This makes the person immune. It prevents further infection because the body responds quickly by producing more antibodies
- The antibodies recognise the antigen (protein shape) on the pathogen
- The MMR vaccination (immunisation) is one of several vaccines. MMR is given to prevent measles, mumps and rubella
- Most people in a population need to be vaccinated to protect society from very serious diseases. This is known as herd immunity
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How do we deal with disease?
- Most people in a population need to be vaccinated to protect society from very serious diseases
- Diseases such as measles can lead to long term damage to the boyd, such as deafness and occasionally death.
- Some vaccines cause side effects which may be mild or serious. So there are advantages and disadvantages of vaccination (immunisation).
- Overuse of antibiotics can lead to the development of new strains of bacteria
- Doctors do not prescribe antibiotics for mild infections such as minor sore throats
- Scientists are always trying to find new ways of treating disease
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