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KS3 Biology
8C Microbes
and Disease
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Contents
8C Microbes and Disease
What are microbes?
Uses of microbes
How microbes cause disease
Fighting disease
Summary activities
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What are microbes?
Microbes are very small
living things and are
sometimes called
micro-organisms.
Microbes are so tiny that they
cannot be seen with the
naked eye. They can only be
seen using a microscope.
How many different microbes
can you name?
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Different types of microbes
There are three types of microbes:
microbes
bacteria
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viruses
fungi
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Bacteria fact file
Bacteria e.g. Salmonella and Streptococcus
size: 1/1000 mm
shape: Bacteria can be spherical,
rod-shaped or comma-shaped.
structure: Bacteria are singlecelled organisms, which do not
completely have a nucleus.
Some cause disease, but many
are useful.
reproduction: Bacteria reproduce
very quickly. Two can very quickly
become four, then eight and so on.
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Bacterium structure
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Viruses fact file
Viruses e.g. flu virus and HIV (the AIDS virus)
size: 1/1,000,000 mm
shape: Viruses have regular
and geometric shapes.
structure: A virus is a simple
organism which does not
display ALL the characteristics
of living things. They are made
up of a protein coating and
some genetic material.
reproduction: Viruses can only
grow and reproduce within other
living things.
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Virus structure
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Fungi fact file
Fungi e.g. Penicillium and yeast
size: Some fungi can actually
be seen with the naked eye,
others are slightly bigger than
bacterial cells.
shape: Fungi come in many
different shapes.
structure: Fungi have the
most complex structures of
all the microbes. They feed
off other living things.
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Fungi (yeast) structure
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Contents
8C Microbes and Disease
What are microbes?
Uses of microbes
How microbes cause disease
Fighting disease
Summary activities
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Using microbes – bacteria and fungi
Microbes have many uses that are based on the fact
that microbes can be grown.
Bacteria grow in milk to make it ‘go
off’.
l  This type of bacterial growth is used
to make milk into yoghurt.
l  Cheese is another product that is
made from milk.
Fungi can also be used to make food. The meat substitute
Quorn is a protein produced using fungi.
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Using microbes – yeast
Yeast is a type of fungus and carries out respiration.
The respiration of this microbe can be used in different ways
in baking bread and in brewing.
The aerobic respiration of yeast is
used to make bread rise.
Yeast uses the sugar in bread dough
to carry out aerobic respiration:
glucose
oxygen
carbon
dioxide
water
energy
What gas produced by the aerobic respiration of yeast
causes bread to rise?
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Using microbes – yeast
The anaerobic respiration of yeast is
used to make beer and wine.
In this case, the yeast respires without
oxygen and produces alcohol (ethanol).
This process is known as fermentation.
Yeast converts the sugar into alcohol
by anaerobic respiration:
glucose
carbon
dioxide
ethanol
energy
How do brewers make sure that yeast respire without oxygen?
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Contents
8C Microbes and Disease
What are microbes?
Uses of microbes
How microbes cause disease
Fighting disease
Summary activities
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Microbes can cause disease
The diseases caused by microbes and their severity depend
on the type of microbe.
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viruses
bacteria
fungi
influenza (flu)
food poisoning
fungal sinusitis
mumps
sore throats
chickenpox
smallpox
tuberculosis
(TB)
tetanus
athlete’s foot
Onychomycosis
polio
cholera
rabies
typhoid
German measles
viral
meningitis
whooping cough
bacterial
meningitis
(causes discoloured
toe nails)
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Which type of microbe?
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How are microbes spread?
The spreading of microbes and disease is known as
transmission.
1. Transmission by air
A cough or a sneeze can release
millions of microbes into the air
which can then infect somebody
else.
2. Transmission by water
Dirty water can transmit many
diseases, e.g. cholera, which
can be transmitted by drinking.
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How are microbes spread?
3. Transmission by animals
An animal can carry a microbe from
one place to another, e.g. a mosquito
which spreads the malaria parasite.
4. Transmission by contact
Many microbes can be exchanged from one
person to another by direct or indirect contact:
l  direct contact by hand;
l  indirect contact, e.g. by walking on a
wet floor already contaminated by
someone else who has athlete’s foot;
l  sexual contact.
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How are microbes spread?
4. Transmission by contact
There are other forms of indirect contact,
e.g. the transmission of microbes from
mother to unborn child.
l  Transmission through the placenta
If the mother develops the HIV/Aids infection,
it can be passed on to the unborn child
through the placenta.
l  Transmission via breastfeeding
If a child is being breastfed, he or she
can also pick up microbes from the
mother via the mother’s milk.
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How is the spread of disease stopped?
The spread of disease can be prevented by making sure
that good hygiene is used in key places such as bathrooms
and kitchens.
Chemicals called antibiotics can be
used to treat bacterial infections.
People can be immunized against
some diseases by the injection of a
vaccine.
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Contents
8C Microbes and Disease
What are microbes?
Uses of microbes
How microbes cause disease
Fighting disease
Summary activities
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Fighting microbes
How does the body fight off microbes that cause disease?
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What do white blood cells do?
The human body has a number of natural defences against
microbes. Noses are hairy inside to trap microbes!
The body also produces
white blood cells to help
defend it from microbes.
Some white blood cells
can destroy microbes
by engulfing them.
white blood cell
antigen
antibody
Some white blood cells are able to produce chemicals
called antibodies. These pairing with matching antigens
on the surfaces of microbes and so help the white blood
cells to engulf microbes.
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White blood cell engulfs microbe – animation
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White blood cell and antibodies – animation
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Contents
8C Microbes and Disease
What are microbes?
Uses of microbes
How microbes cause disease
Fighting disease
Summary activities
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Glossary
l  antibiotics – Chemicals prescribed as medicine to kill
bacteria inside the body.
l  antibodies – Chemicals produced by white blood cells
to fight microbes that cause disease.
l  bacteria – The type of microbes that are single-celled
organisms.
l  fungi – The type of microbes that feed off other living
things.
l  immune – Resistance to infection caused by a microbe.
l  microbe – A very small living thing.
l  transmission – The spread of a disease from person to
person.
l  viruses – The type of microbes that can only grow and
reproduce within other living things.
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Anagrams
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Multiple-choice quiz
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