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KS3 Biology
8C Microbes
and Disease

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8C Microbes and Disease
Contents
What are microbes?
Uses of microbes
Summary activities
How microbes cause disease
Fighting disease

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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.
What are microbes?
How many different microbes
can you name?

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There are three types of microbes:
Different types of microbes
bacteria viruses fungi
microbes

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Bacteria fact file
size: 1/1000 mm
shape: Bacteria can be spherical,
rod-shaped or comma-shaped.
structure: Bacteria are single-
celled 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.
Bacteria e.g. Salmonella and Streptococcus

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Bacterium structure

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Viruses fact file
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.
Viruses e.g. flu virus and HIV (the AIDS virus)

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Virus structure

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Fungi fact file
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.
Fungi e.g. Penicillium and yeast

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Fungi (yeast) structure

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8C Microbes and Disease
Contents
What are microbes?
Uses of microbes
Summary activities
Fighting disease
How microbes cause disease

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Microbes have many uses that are based on the fact
that microbes can be grown.
Fungi can also be used to make food. The meat substitute
Quorn is a protein produced using fungi.
Bacteria grow in milk to make it ‘go off’.
 This type of bacterial growth is used
to make milk into yoghurt.
 Cheese is another product that is
made from milk.
Using microbes – bacteria and fungi

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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:
What gas produced by the aerobic respiration of yeast
causes bread to rise?
Using microbes – yeast
carbon
dioxideglucose oxygen water energy

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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:
Using microbes – yeast
carbon
dioxideglucose ethanol energy
How do brewers make sure that yeast respire without oxygen?

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8C Microbes and Disease
Contents
What are microbes?
Uses of microbes
Summary activities
Fighting disease
How microbes cause disease

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The diseases caused by microbes and their severity depend
on the type of microbe.
viruses bacteria
influenza (flu) food poisoning
mumps sore throats
chickenpox tuberculosis
(TB)smallpox tetanus
polio cholera
rabies typhoid
German measles whooping cough
fungi
fungal sinusitis
athlete’s foot
Onychomycosis
(causes discoloured
toe nails)
viral
meningitis
bacterial
meningitis
Microbes can cause disease

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Which type of microbe?

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Microbes can enter the body in many different places.
How do microbes enter the body?
eyes
mouth
cuts
nose
ears
How are the diseases caused by microbes spread?
genitals
skin

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The spreading of microbes and disease is known as
transmission.
How are microbes spread?
A cough or a sneeze can release
millions of microbes into the air
which can then infect somebody
else.
1. Transmission by air
Dirty water can transmit many
diseases, e.g. cholera, which
can be transmitted by drinking.
2. Transmission by water

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How are microbes spread?
An animal can carry a microbe from
one place to another, e.g. a mosquito
which spreads the malaria parasite.
3. Transmission by animals
Many microbes can be exchanged from one
person to another by direct or indirect contact:
4. Transmission by contact
 direct contact by hand;
 indirect contact, e.g. by walking on a
wet floor already contaminated by
someone else who has athlete’s foot;
 sexual contact.

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 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.
If the mother develops the HIV/Aids infection,
it can be passed on to the unborn child
through the placenta.
 Transmission through the placenta
How are microbes spread?
There are other forms of indirect contact,
e.g. the transmission of microbes from
mother to unborn child.
4. Transmission by contact

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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.
How is the spread of disease stopped?

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8C Microbes and Disease
Contents
What are microbes?
Uses of microbes
Summary activities
Fighting disease
How microbes cause disease

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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!
Some white blood cells
can destroy microbes
by engulfing them.
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.
white blood cell
antibody
antigen
The body also produces
white blood cells to help
defend it from 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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8C Microbes and Disease
Contents
What are microbes?
Uses of microbes
Summary activities
Fighting disease
How microbes cause disease

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Glossary
antibiotics – Chemicals prescribed as medicine to kill
bacteria inside the body.
antibodies – Chemicals produced by white blood cells
to fight microbes that cause disease.
bacteria – The type of microbes that are single-celled
organisms.
fungi – The type of microbes that feed off other living
things.
immune – Resistance to infection caused by a microbe.
microbe – A very small living thing.
transmission – The spread of a disease from person to
person.
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