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What you need to know!
Reflections and exam tips
Disease and Immunity
Is a state of unwellness, comes from 2 roots:
dis = not
ease = calmness
Diseases can be caused by pathogens (germs- don't use this term in exams), shortage of essential nutrients from a diet, physical damage to organs or even an imbalances of the body systems such as the nervous system.
Pathogens- a pathogen is a microorganism that causes a disease. Note that some microbes do not cause diseases. We eat some of them (mushrooms, bacteria in natural yoghurt and yeast used to make beer and bread).
Diseases caused by pathogens are usually infectious (spreadable).
Your need to know (name the parts) the structure of each of the 3 main pathogenic microbes; bacteria, viruses and fungi and explain how they cause disease.
The 3 main types of pathogens:
Bacteria are made up of cells, which can be a variety of shapes ranging from circular, rod-shaped to comma-shaped.
They belong to a group of organisms called Prokaryotes, organisms without a true nucleus. This means that they are very simple, with no membrane-bound organelles like mitochondria.
How they cause disease
Viruses are not made up of cells. They are made of:
How they cause disease:
Viruses cause disease by the way they reproduce:
The problem with visruses
Fungi are made up of cells. Some are unicellular and some are multicellular. They can be spherical cells like yeast while some are fibrous hyphae, like bread mould.
How they cause disease
Means resistance to an infection.
The body has natural barriers which stop pathogens from going into cells. These are:
These depend on the ability of the body to recognise foreign substances coming in. Each pathogen has protein markers called antigens on its surface. These help the body to detect if an invader has come in.
Internal defences work if microbes have managed to enter the body systems and cells:
These depend on the blood which is made up of:
The white blood cells play a major role in immunity. There are 2 types of white blood cells:
Lymphocytes produce ptoteins called antibodies, which stick to antigens on the pathogen's surface. This may either:
Besides this, lymphocytes produce memory cells which are stored in the body. These already recognise the pathogen, if it comes back again, they produce antibodies faster and in large amounts before the pathogen causes infection.
Phagocytes detect the pathogen's antigen, engulf pathogens. This means that they surround, take in and digest them.
Types of immunity
1. Natural immunity:
When you catch an infection, your body produces antibodies and memory cells which protect you against future infections.
Babies also acquire antibodies from their mothers during breastfeeding.
2. Artificial immunity- Vaccination
This is sometimes called immunisation or vaccination.
During vaccination, weakened (attenuated) or dead pathogens are injected into the body. Sometimes only antigens from the pathogen are used. The body reacts by producing antibodies and memory cells which protect you from real infections later.
Semmelweis- 'The saviour of mothers'
Ignaz Semmelweis was a Hungarian doctor working at Vienna General Hospital. He showed how handwashing with disinfectant could reduce the transfer of pathogens from one patient to another. He hypothesized that doctors were routinely transmitting pathogens from dissecting corpses to new mothers as they did not wash their hands. As such mothers were dying of childbirth fever. This was in contrast to low death rates in wards which were worked by nurses only who did not handle dead bodies. Semmelweis then advised his trainees to wash their hands in disinfectant before helping mothers give birth. This was followed by a significant reduction in the death rates.
Why is Semmelweis's work still important?
1.Find out about MRSA. What is it? Why is it a problem.
2. What is antibiotic resistance? How does it arise. Use the concept of Natural selection to explain how antibiotic resistance arises.
3. Write a 6 mark essay explaining how white blood cells protect us from infection.