Biology
- Created by: Zhraa
- Created on: 09-04-14 16:52
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- Keeping Healthy
- Defending against infection
- Pathogens
- Pathogens are microorganisms - such as bacteria and viruses - that cause disease. Bacteria release toxins, and viruses damage our cells. White blood cells can ingest and destroy pathogens by producing antibodies that destroy the infectious microorganisms, and antitoxins to neutralise toxins created as a by-product.
- Bacteria
- Bacteria and viruses are the main types of pathogen. Bacteria are microscopic organisms. They come in many shapes and sizes, but even the largest are only 10 micrometres long - that's 10 millionths of a metre.
- Bacteria are living cells and, in favourable conditions, can multiply rapidly. Once inside the body, they release poisons or toxins that make us feel ill.
- Diseases caused by bacteria include:
- food poisoning
- typhoid
- whooping cough.
- cholera
- Diseases caused by bacteria include:
- Medicine
- Some medicines help to relieve the symptoms of a disease while others kill the infectious pathogens.
- Pain Killers
- Painkillers helps to relieve the symptoms of an infectious disease, but they do not kill the pathogens involved. For example, paracetamol, aspirin and morphine block nerve impulses from the painful part of the body, or block nerve impulses travelling to the part of the brain responsible for perceiving pain.
- Antibiotics
- Antibiotics are substances that kill bacteria or stop their growth. They do not work against viruses because they live and reproduce inside cells. It is difficult to develop drugs that kill viruses without also damaging the body’s tissues.
- Penicillin, the first antibiotic, was discovered in 1928 by Alexander Fleming. He noticed that some bacteria he had left in a Petri dish had been killed by naturally occurring penicillium mould. Since the discovery of penicillin, many other antibiotics have been discovered and developed.
- Different antibiotics work in different ways. It is important that specific bacteria should be treated using specific antibiotics
- Antibiotic resistance
- MRSA
- MRSA is the acronym for 'methicillin-resistant Staphylococcus aureus'. It's very dangerous because it's a strain of bacterium that is resistant to most antibiotics.
- To slow down or stop the development of other strains of resistant bacteria, we should always:
- avoid the unnecessary use of antibiotics
- complete the full course.
- The appearance of resistant strains of bacteria means that vaccinations and antibiotics may no longer work. As people are not immune to it, and there is no effective treatment, a resistant strain will spread rapidly. New antibiotics must be developed as a result.
- Bacterial strains can develop resistance to antibiotics. This happens because of natural selection. In a large population of bacteria, there may be some cells that are not affected by the antibiotic. These cells survive and reproduce, producing even more bacteria that are not affected by the antibiotic.
- Development of resistance
- The main steps in the development of resistance are:
- resistant individual pathogens survive and reproduce
- antibiotics kill individual pathogens of the non-resistant strain
- the population of the resistant pathogens increases.
- The rate of development of resistant strains of bacteria can be slowed down. One way to do this is to avoid using antibiotics for infections that are not serious, such as mild throat infections.
- The main steps in the development of resistance are:
- MRSA
- Growing organisms in a lab
- In 1878 Robert Koch discovered how to grow bacteria in a Petri dish (named after his assistant Julius Petri). He was able to discover which bacteria caused certain diseases, including TB and cholera. Scientists still grow microorganisms in the lab so that they can be investigated.
- Culturing microorganisms
- The action of antibiotics and disinfectants can be investigated using cultures of microorganisms (populations of microorganisms that have been grown for a purpose).
- It is important that the cultures are uncontaminated by other microorganisms, so sterile conditions are needed:
- the Petri dishes, nutrient agar jelly and other culture media must be sterilised
- the inoculating loops used to transfer microorganisms must be sterilised (usually by passing the metal loop through a Bunsen burner flame)
- the lid of the Petri dish is sealed with sticky tape to stop microorganisms from the air getting in and contaminating the culture.
- Safety in the lab
- Bacteria grow and reproduce more quickly when they are warm than when they are cold. It would be dangerous to incubate (keep and grow) cultures at temperatures close to body temperature (37°C) because doing so might allow the growth of pathogens harmful to health. So the maximum temperature used in school and college labs is 25°C. However, higher temperatures can be used industrially, and these produce faster growth.
- Pathogens
- Defending against infection
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