Bacteria are single-celled microorganisms that are found everywhere on Earth. They come in different shapes and sizes, and some have flagella or slime to help them move. Bacteria play important roles in ecosystems by breaking down dead materials and producing oxygen. Trillions of bacteria live in the human gut and help with digestion. Bacteria were the earliest forms of life on Earth and their production of oxygen allowed other lifeforms to develop.

1. Bacteria 1
Bacteria Basics
• Many of us know bacteria only as ‘germs’,
invisible creatures that can invade our
bodies and make us ill. They live in, on
and around us all the time.
• Not everyone knows that bacteria also do
lots of good things, like break down dead
leaves and other rubbish, and make
oxygen.
• We can even use bacteria, making them
work for us!
• Bacteria consist of only a single cell each,
whereas each one of you is made up of
about 10,000,000,000,000 cells! But
don’t start feeling superior – bacteria are
amazing, and very important! Without
them, you couldn’t even survive!
• If there is just one of them, we call it a
bacterium.
These bacteria turn milk into yoghurt! These bacteria give you a sore throat!

2. Bacteria 2How They Get Around
• Bacteria have many different shapes.
Some have 'tails' (called flagella) that let
them swim. They rotate their flagella like
tiny propellers to move themselves
through liquids.
• Other bacteria make slime so they can
ooze over surfaces like slugs.
• Others stay almost in the same spot.
What They Look Like
• There are thousands of types of bacteria.
Some are rod-shaped; others are shaped
like little balls. Some are spirals.
• You could fit 1000 of them across 1 mm!
Pretty, but hard to
draw!
Draw this one – it’s
simpler!

3. Bacteria 3Where They’re Found
• Bacteria can be found almost everywhere!
• Bacteria live on or in just about every
material and place on Earth, from soil to
water to air, and from your body to the North
Pole to the Sahara desert.
• Many types can survive below freezing
temperature (0°C)., and some types can
survive above boiling point (100°C).
This picture was taken with a very
powerful microscope. This bacterium
lives in soil, and moves through soil
water using its flagella.
• Lots of them live on you, but don’t worry,
almost all of them are good for you! Each
square centimetre of your skin has about
100,000 bacteria on it.
This picture shows bacteria on human skin.
(They aren’t really bright pink; they’ve been
coloured in pink so you can see them better.)
That big tree trunk in the picture is actually a
human hair. So now you can see how small
bacteria are!

4. Bacteria Extras 1
Read at your own risk – this may shock you!
How Long They’ve Been Around
• Like dinosaurs, bacteria left behind
fossils. The big difference is that it takes
a microscope to see them. And they are
older.
• Bacteria were the earliest forms of life on
Earth. They first appeared about 4 billion
years ago, and for the next 2 billion years
they were the only life on Earth!
Without Bacteria, We Could Never Have
Existed!
• Earth was a poisonous place back in the early days.
There was no oxygen around, so we and most other
animals and plants could not have existed.
• Then some types of bacteria started making oxygen
using the energy from sunlight – they had invented
photosynthesis! Once plenty of oxygen had built up
in the atmosphere, it became possible for plants
and animals to develop. So bacteria paved the way
for us! Thank you, bacteria!
Bacteria fossil, 3 million years old
Earth might have looked like this in the early days.

5. Bacteria are Different From All
Other Living Things!
• Like us, bacteria have DNA, or genes,
inside the cell. But unlike ours, their
DNA is not contained in the little package
we call the nucleus. It just floats around
in the cytoplasm.
• Different types of bacteria eat different
foods. Some eat sugar and starch; others
eat sulfur, or even iron!
• Others use sunlight to make their own
food, like plants do.
Bacteria Extras 2
Read at your own risk – this may shock you!
This twisty-looking bacterium eats
iron for its dinner! Weird!
Someone has knitted this
bacterium! (Real ones don’t have
eyes, of course. Or ears, or
noses. But they can find their way
around by detecting different
chemicals around them.)

6. The Bacteria in YOU!
• There are 100 trillion (100,000,000,000,000)
bacteria – weighing 2 ½ kilos altogether -
happily living in your intestines. That's ten
times more bacteria than there are cells in your
body, more bacteria than the number of stars
in our galaxy, more bacteria than the number of
humans who have ever lived (estimated, by the
way, at 100 billion) ... You get the picture. There
are a lot.
• To an alien landing on our planet, we humans
might just seem like a chain of bacteria hotels!
Bacteria Extras 3
Read at your own risk – this may shock you!
This is one of the types of ‘good’
bacteria that live in people’s intestines.
The makers of
this ‘probiotic’
yoghurt claim
that the bacteria
in it are good for
your digestive
system.
Whether or not
that’s true, they
are certainly
safe to eat.
• Babies are born with no bacteria in
their intestines, but within a few
weeks bacteria have got in and made
their home there.
• Without these bacteria in our guts, we
would have difficulties digesting all our
food, and we would become unwell.

7. The Bacteria in YOU!
• There are 100 trillion (100,000,000,000,000) bacteria –
weighing 2 ½ kilos altogether - happily living in your
intestines. That's ten times more bacteria than there
are cells in your body, more bacteria than the number of
stars in our galaxy, more bacteria than the number of
humans who have ever lived (estimated, by the way, at
100 billion) ... You get the picture. There are a lot.
• To an alien landing on our planet, we humans might just
seem like a chain of bacteria hotels!
Bacteria Extras 3
Read at your own risk – this may shock you!
This is one of the types of ‘good’
bacteria that live in people’s intestines.
The makers of
this ‘probiotic’
yoghurt claim
that the bacteria
in it are good for
your digestive
system.
Whether or not
that’s true, they
are certainly
safe to eat.
• Babies are born with no bacteria in
their intestines, but within a few
weeks bacteria have got in and made
their home there.
• Without these bacteria in our guts, we
would have difficulties digesting all our
food, and we would become unwell.