Download KS4 Microbes

Contents
Microbes
What are microbes?
Bacteria and viruses
Microbes and disease
How do microbes reproduce?
Summary quiz
What causes disease?
Why do people become ill?
People who lead very unhealthy lifestyles sometimes
become ill but it is also clear that people can become ill
despite leading a healthy lifestyle. Why?
Therefore, rather than something being wrong with that
person, perhaps something else changes the normal state
of the body and causes disease.
These were eventually discovered to be…
MICROBES
Microbes
As the name suggests, they are microscopic organisms.
They can only be seen
using a microscope.
Microbes
The two kinds of microbe that we will be dealing with are:
BACTERIA
VIRUSES
Now it is important at this point to remember what it
means to be living organism.
A living organism must be able to demonstrate that it
can perform the seven life processes.
The seven signs of life
Microbes
The reason for looking back to these 7 characteristics is
because although bacteria can perform all of these life
processes, viruses cannot reproduce on their own.
Does this mean
that viruses are
non-living?
This question is still hotly debated!
Microbes
Bacteria have a traditional cell structure, as with animals and
plants. Viruses do not.
Let us firstly consider what these microbes look like and how
they compare to the structure of cells that we are familiar
with.
We will firstly deal with the general structure of a bacterium
(singular of bacteria).
Bacteria are amongst the smallest known to mankind.
Contents
Microbes
What are microbes?
Bacteria and viruses
Microbes and disease
How do microbes reproduce?
Summary quiz
A single bacterium
Bacteria can be different shapes but this diagram can
represent them.
cell wall
cell
membrane
present in animal cells
absent from animal cells
cytoplasm
loose genetic
material
Bacterium
So, the bacterium shares some structural characteristics
with an animal cell but shows important differences. The
most obvious differences are:
the absence of a distinct nucleus
the presence of a cell wall
The other major difference is the size of the cell.
To get an idea of how small these cells are, remember
that the human body consists of approximately 100
million animal cells.
Bacteria cells are 10-1000 times smaller than
animal cells.
Bacterium
If we wanted to measure a single bacterium, its length
would range from:
1
1
mm to
1000
mm
20
If a full stop is 1mm wide how many bacteria could you
line up along it?
Between 1000 and 20 bacteria would fit on a full stop!
Virus
Now let’s consider the structure of the virus.
injection
tube
protein
coat
loose genetic
material
tail plate
Absent in animal cells
Viruses - how small?
Viruses are very different to bacteria
because they do not have a cellular
structure and are much smaller.
Bacteria are 100 times smaller than a human cell.
Viruses are 1000 times smaller than a bacteria.
So how small are viruses compared to a human cell?
100 000 times smaller!
Viruses and tennis balls!
Here’s another way to think about the size of viruses...
If a common cold virus was
the size of a tennis ball,
how big would a nose be?
A. the size of a supermarket
B. the size of Birmingham
C. the size of Wales
Viruses – living or not?
If viruses are such tiny microbes,
how do they cause so much havoc?
Viruses need to hijack a host cell,
like a human body cell, in which to
live and make more viruses.
Viruses cannot function if they are
outside of a host cell.
Some scientists say that viruses are not ‘alive’ because of
how they reproduce. Would you say a virus was living or not?
Bacterium – label the parts
Virus – label the parts
Virus and bacterium properties
Contents
Microbes
What are microbes?
Bacteria and viruses
Microbes and disease
How do microbes reproduce?
Summary quiz
Viruses and bacteria
You probably know more about bacteria and viruses than
you think.
The following illnesses are all caused by microbes infecting
the human body. How many do you recognise?
Common illnesses
Most people have suffered from at least one of these illnesses:
VIRUSES
BACTERIA
Influenza (flu)
Food poisoning
Mumps
Sore throats
Chickenpox
Tuberculosis (TB)
Smallpox
Tetanus
Polio
Cholera
Rabies
Typhoid
German measles
Whooping cough
So, how do these microscopic organisms actually cause
illness in such a complex and relatively enormous
organism like a human being?
Under attack!
Firstly, as soon as a virus or bacterium enters the
body, we are termed infected.
This is not the same as being ill.
Illness results from the effects these microbes have
on our body.
Bacteria and viruses have the ability to produce
poisons known as...
TOXINS
Under attack!
When the microbe enters the body, it begins
releasing these toxins which can damage body
tissue and prevent body systems working properly.
The body could probably cope with a small amount of poison,
but microbes quickly reproduce themselves.
If the microbes
reproduce…
We are said to be diseased.
more microbes mean that
more toxin produced…
our normal state of well being is affected…
Diagram of a microbe attack
These symbols and colours
represent the process of becoming
infected and then ill:
1
Person is well. The
microbe levels are
very low and the toxin
levels are very low.
2
Person is infected.
The microbe levels
are low and the toxin
levels are low.
Toxin Levels
Presence of microbes
3
Person is ill and
diseased. The microbe
levels are high and the
toxin levels are high.
Which microbe causes which disease?
The process of disease
Contents
Microbes
What are microbes?
Bacteria and viruses
Microbes and disease
How do microbes reproduce?
Summary quiz
Bacteria reproduction
Bacteria can reproduce quickly and independently .
One bacterium can divide into two new bacteria
every 20 minutes!
Bacteria reproduction
This means that if 1 bacterium enters your body
at 8.00am, 4 hours later, you would have 4096
bacteria within your body!
Do viruses reproduce in the same way as bacteria?
No!
Virus reproduction
Viruses need a host cell to reproduce within.
This is a body cell, which will provide the machinery, and
chemicals the virus requires to make copies of it.
host cell
e.g. a human body cell
virus
The process of host cell infection
Therefore the virus not only infects the body; it
also infects the body cells.
1. Approach
The virus
approaches
the host cell
2. Attachment
The virus secures
itself to the surface
of the host cell.
The process of host cell infection
3. Insertion
The virus injects its
genetic material
through the
injection tube and
into the host cell.
4. Replication
The genetic
material makes
multiple copies of
itself.
The process of host cell infection
5. Assembly
New viruses are
assembled using
chemicals from the
host cell. The
original virus dies
and breaks down.
It is at this stage that the viruses within the host cell
can remain dormant. In other words, they sit within the
cell without killing it or breaking out. With some viruses
such as HIV, this period can last a number of years.
This is why people can remain infected with HIV
without realizing they are infected.
The process of host cell infection
6. Cell Lysis (cell breaks)
- toxin
The host cell splits open and dies. The viruses
escape and release toxins.
Each virus will then start another round of
replication.
Virus reproduction - what’s the order?
Virus reproduction - explain it!
Contents
Microbes
What are microbes?
Bacteria and viruses
Microbes and disease
How do microbes reproduce?
Summary quiz
Microbes quiz