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The good or the bad?
• Microbes are normal
We live with microbes all the time. These
microbes are our normal flora. They are on
our skin and inside our gut. They don’t usually
cause disease and they can even help to
protect us from infection by harmful microbes.
Harmful, disease-causing microbes are called
pathogens.
Heath and disease
• Good health is priceless. Bad health
can mean poor quality of life and a
shorter lifespan. So why are some
people unhealthy? There can be many
different reasons, including lifestyles
and accidental injuries. We are going to
look at one important cause of disease:
infection by microbes.
What are microbes?
Microbes may be divided into three areas;
• Virus
• Bacteria
• Fungi
Viruses
• Virus particles are tiny: about 0.00002 to
0.0003mm.
• They are not complete cells but consist only
of a protein coat surrounding genetic
material, DNA or RNA.
• Viruses always reproduce inside other cells,
which are usually killed in the process. The
ringworm fungus.
DNA
Protein coat
End-plates
Examples of illness which
viruses cause
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HIV
smallpox
the common cold
Chickenpox
Influenza
Shingles
Polio
herpes,
rabies
Bacteria
Ranging from 0.0001 to 0.02mm in length,
bacteria are the smallest form of life that can
live independently.
They are single-celled: each cell is a separate
working unit. There are two main shapes for
bacteria: round (e.g. streptococcus) or rod
shaped.
Bacteria tend to be round or rod shaped.
Rod
Shaped
Round
shaped
Illness which bacteria cause..
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Salmonella
Infections
pneumonia
meningitis
ringworm and athlete's foot
food-poisoning.
Fungi
• Yeasts and moulds are both examples of
fungi. Yeasts are single-celled, often growing
on rotten fruit and cause fermentation. They
vary in size, but are big enough to see
without a microscope.
• There are many different sorts of protozoa.
They all live in wet environments. Most can
move around.
• They vary in size from 0.01 to 0.2mm. Some
protozoa, such as amoebae, cause a serious
gut disorder called dysentery.
Bacteria and reproduction
• Bacteria are all around us. Given good
growing conditions, a bacterium grows
slightly in size or length, a new cell wall grows
through the centre forming two daughter
cells, each with the same genetic material as
the parent cell. If the environment is optimum,
the two daughter cells may divide into four in
20 minutes.
If they divide so quickly then ….
• Then why isn't the earth covered with
bacteria?
• The primary reason may be that conditions
are rarely optimum. Scientists who study
bacteria try to create the optimum
environment in the lab: culture medium with
the necessary energy source, nutrients, pH,
and temperature, in which bacteria grow
predictably.
Are microbes/bacteria
good or bad?
Bacillus thuringiensis (bah-sill-us therin-gee-in-sis): a.k.a "Bt", a common
soil bacterium. Wanted as a natural
pest-killer in gardens and on crops
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Streptomyces (strep-toe-myseas): soil bacteria wanted for
making streptomycin, an
antibiotic used to treat
infections.
• Pseudomonas putida (sue-doe-moanus poo-tea-dah): one of many microbes
wanted for cleaning wastes from
sewage water at water treatment
plants.
Friend or foe?
• There are many other important jobs
microbes do. They are used to make
medicine.
• They break down the oil from oil spills.
They make about half of the oxygen we
breathe.
• They are the foundation of the food
chain that feeds all life on earth.
• In short, microbes are much more our
friends than our enemies.