Viruses are the smallest type of microbe that can only reproduce inside host cells. Unlike bacteria, viruses cannot move on their own and come in various shapes and sizes. Viruses are found almost everywhere in the environment from soil and water to air, waiting to infect plant, animal, and bacterial cells. When a virus infects a cell, it takes over the cell's machinery to reproduce itself before causing the cell to burst and release new virus particles to infect neighboring cells.

1. 1
Virus Basics
• Viruses are the smallest type of microbe,
even smaller than bacteria.
• Viruses are really the bad guys of the
microbe world. They don’t do anything that
we would call good. (Only in the last few
years have scientists come up with ways of
making viruses do useful things for us…)
• Viruses are strange things that are somehow
in between being alive and not alive. If they're
floating around in the air or sitting on a
doorknob, they do absolutely nothing. They're
about as alive as a rock. But if they come into
contact with a suitable plant or animal cell,
they spring into action. They infect and take
over the cell like pirates hijacking a ship.
• As a virus cannot reproduce without using
another creatures’ cells to help it, some people
are not convinced that viruses are really living
things.
This virus gives you flu! This virus gives you a cold!

2. 2
How They Get Around
• Unlike bacteria, viruses can’t move
themselves around.
• But once a virus has got into another
creature’s cell and used it to make new
copies of itself, the cell bursts, and the
new virus copies get shot off into the
cells next door.
What They Look Like
• There are thousands of types of virus
that come in many shapes.
• Many have geometric shapes, like cut
diamonds. Others are shaped like spiky
eggs, skinny sticks or pieces of looped
string. Some are more complicated and
look like tiny spaceship landing pods.
• Viruses don’t have a nucleus. Their DNA
(genes) just floats around inside them.
They aren’t really even proper cells.
Draw this
simple one:
This is a picture
taken with a
microscope,
showing a virus
attacking a cell.
Don’t draw it –
it’s too
complicated.

3. 3
Where They’re Found
• Viruses can be found almost everywhere!
They’re all over the planet, in soil, water
and air, just waiting around for cells to
infect.
• Viruses can infect every living thing.
However, they tend to be picky about
what type of cells they infect. Plant
viruses do not infect animal cells, for
example.
When you have a
cold and you sneeze,
the cold virus is in the
drops that shoot out
of your nose and
mouth! If it lands on
someone else, it gets
to work on them…
…so use a tissue!
This virus hangs
around in soil, and
infects wheat.

4. Extras
Read at your own risk – this may shock you!
Viruses are Really, Really
Tiny
• Even compared with bacteria (and
your own cells), viruses are very
small.
• Viruses don’t just attack cells of
humans, other animals, and plants.
They even attack bacteria!
• If you lined up a million of them,
they would only cover 1 mm in
length!