Transcript microbesanddiseases

Micro-organisms and Diseases (Year 8)
Mike Turner, Mar. 2004
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Micro-organisms and Diseases (Year 8)
Types of Microbe
What we often call germs are in fact micro-organisms such as bacteria, viruses and fungi. They are much
too small to be seen with the naked eye.
There are millions of types of bacteria, fungi and viruses. Some of them are harmful to us, but many are
not.
E. coli, a bacterium which
lives inside humans.
A type of flu virus.
Mike Turner, Mar. 2004
Athlete’s foot.
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Micro-organisms and Diseases (Year 8)
Bacteria
Bacteria are living cells. They are found in most places. They are much larger than viruses.
Some bacteria cause diseases, such as food poisoning, but many are harmless.
The structure of a bacterium is like this :
They do not have a nucleus, but do have a cell wall, cell membrane, and cytoplasm.
Bacteria can reproduce quickly, but their reproduction is slowed down at lower temperatures. This is the
main reason that food stays fresh longer in a fridge.
Mike Turner, Mar. 2004
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Micro-organisms and Diseases (Year 8)
Culturing Bacteria
In the laboratory, bacteria can be grown, or cultured, in a Petri dish.
The dish contains a culture medium for the bacteria to grow on. This has nutrients for the bacteria to feed on.
The culture medium needs to be inoculated with bacteria initially. The bacteria will then reproduce.
Mike Turner, Mar. 2004
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Micro-organisms and Diseases (Year 8)
Culturing Bacteria - Safety
There are several safety precaution that must be taken when working with micro-organisms :
Precaution
Reason
Use a sterilised Petri dish.
No unwanted bacteria already in the dish will
grow.
Never inoculate from areas of the body that
may contain harmful bacteria, eg inside the
nose or mouth.
There is less chance that harmful bacteria will
develop in the culture.
Fix lid firmly in place.
Bacteria will be unable to escape from or enter
the dish.
Ensure the edges of the dish are not completely
sealed.
Oxygen can enter the dish, so anaerobic
bacteria (which are often harmful), will not
develop.
Never store the culture at human body
temperature (37 degrees celsius).
At body temperature, bacteria that infect
humans will grow very quickly.
Store the inoculated culture upside down.
Any droplets of water than condense inside the
container will not fall onto the culture.
Mike Turner, Mar. 2004
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Micro-organisms and Diseases (Year 8)
Viruses
Viruses are very small, much smaller than bacteria.
Some scientists do not classify viruses as living organisms.
This is because they do not need nutrition (and as they do not
eat, they do not excrete).
The SARS virus.
(There are 1,000,000 nm
in 1 mm)
Viruses do not have any of the structures found in normal cells. They have a protein coating rather
than a cell membrane. They contain a strand of DNA, and to reproduce they infect a host cell with
this DNA.
A virus approaches a bacterial cell
The virus injects DNA into the cell
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Micro-organisms and Diseases (Year 8)
The Effects Of Viruses On Cells
The viruses’ DNA then takes over the cell, and makes copies of itself. As this happens in many cells,
millions of copies of the virus are made.
A cell is attacked by viruses (left).
So many copies are produced as the virus reproduces, that
eventually the cell bursts open, and the new viruses
escape to infect other cells.
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Micro-organisms and Diseases (Year 8)
Fungi
Yeast, penicillin and athlete’s foot are all members of the fungus family, as are mushrooms.
Fungi grow well in warm, moist, dark conditions, such as between the toes! To avoid athlete’s foot, it is
important to keep the feet cool and dry.
Yeast is a type of fungus that is used in producing bread. It produces
carbon dioxide as it respires, which makes the dough rise.
Yeast is also used to produce alcohol.
An important use of fungi is to produce antibiotics, such as penicillin.
Antibiotics are used to treat bacterial infections – they attack and kill
bacteria.
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Micro-organisms and Diseases (Year 8)
Spreading Disease
Diseases can spread in many different ways. These include :
• Person to person - Bacteria and viruses can pass from person to person by blood, saliva or by being coughed
or sneezed into the air.
• Food borne infection – Food that has not been stored correctly, or has been stored for a longer time than it
ought to be, will contain lots of bacteria. Also, if an infected or unclean person prepares food then the
infection will pass to the people that eat the food.
• Water borne infection – When water is not properly treated, it can contain many sources of infection.
• Airborne infection – Some diseases can spread through the air. A dangerous one is Legionnaire’s disease,
which can be spread by badly maintained air conditioning systems.
• Insect borne infection – Many diseases can be spread by insects, when they bite humans, for example the
plague.
(Borne means ‘carried by’).
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Micro-organisms and Diseases (Year 8)
The Body Fights Back
We are surrounded by micro-organisms, many of them harmful. They live around us, on us and in us. Even so, we
rarely get ill.
The body contains a number of defences that fight off the invaders.
When you breathe in through the nose, small hairs inside it act as a filter to trap dust and some microorganisms. Sticky mucus in the airways also traps many microbes. They are then removed from the body when
you cough, sneeze or blow your nose.
If you cut yourself, platelets from the blood will clot and form a scab,
stopping microbes from entering the body and stopping the blood from
leaking out.
White blood cells rush to the site to attack the microbes that have
entered. The white blood cells surround the micro-organisms and ‘eat’ them.
They also produce antibodies – chemicals which weaken or destroy the
micro-organisms.
White blood cells
travel to the site of
a wound.
White blood cells are carried in the blood, and also in the lymph system.
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Micro-organisms and Diseases (Year 8)
A Helping Hand
When a person has been infected with a particular microbe, the body can produce the correct antibodies
very quickly if that type of microbe attacks again.
The person is now immune to that disease.
If a person is deliberately given some dead or weak microbes,
then the body will learn to produce antibodies to attack that
microbe, and so will be immune to that disease in the future.
This is called vaccination. We say the person has been
immunised against the disease.
The dead microbes that are put into the body are called
vaccines.
This is the bacterium that causes
tuberculosis (TB). The BCG injection you
have in your upper arm is a vaccination that
immunises you against TB.
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Micro-organisms and Diseases (Year 8)
Some Definitions
Can you match the terms and their definitions? Click the mouse to see the answers.
Immune
A very small organism, such as a bacterium, virus or fungus.
Micro-organism
A chemical that is produced by white blood cells, which kills or
weakens micro-organisms.
Epidemic
When a disease spreads very quickly to a lot of people.
Vaccine
Antibody
Safe from a particular disease.
A substance containing dead or altered micro-organisms, which is put
into the body to give you immunity from a disease in the future.
Mike Turner, Mar. 2004
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Micro-organisms and Diseases (Year 8)
You have now reached the end of the revision presentation for the ‘Micro-organisms and
Diseases’ topic.
I hope you have found it useful. If you have any ideas to improve this presentation please let
Mr. Turner know.
Thank you for looking at this work, and good luck in your test.
Mike Turner, Mar. 2004
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