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A Level Biology: Microorganisms and Health 1 – Microorganisms
Hi! Welcome to my first video on the series about Microorganisms and Health. The first
thing we’re going to look at are the types of things which can cause disease. The first
of these are microorganisms. There are three main types. There are fungi, bacteria and
viruses. You can see here, this diagram that we got on the top, this shows us that the
three of these, the largest is fungi, the next is bacteria, and then viruses.
These measurements that you have here corresponding to this virus are nanometers. Now, if we divide
a meter, we can divide a meter into millimeters and then subsequently, micrometers and then
into nanometers. A nanometer is basically a meter divided into a billion. If you imagine
one meter divided into a billion parts, those can be in some cases a smallpox virus that
is about 200 nanometers long or wide and therefore, is particularly small.
Bacteria are types of microorganisms that require a couple of things in order to grow.
Usually, they need a food source and they need a source of moisture and heat. They can
grow in a number of different environments. One way to coach or grow bacteria is to grow
them on what is known as an agar plate, which is what is shown here. The agar provides the
bacteria with food so it can colonize and it can multiply.
Viruses, on the other hand, are slightly different. What viruses do is they work by infecting
host cells and that can be bacterial cells, that can be human cells and they use the mechanisms
within the cells in order to reproduce.
There is a term that we can use to describe microorganisms that means they cause disease
and that word is “pathogenic”. A microorganism that causes a disease is sometimes referred
to as pathogen.
We got some examples of pathogens here. A type of fungus that causes disease, e.g.,
Athlete’s foot and Thrush, specifically the one that causes rashes called Candida.
Viruses that are pathogenic are the smallpox and flu. Bacterial infections which are pathogenic
are tuberculosis and cholera.
What this means is that not all microorganisms are bad for you; not all of them cause disease
but the few that do are referred to as pathogens. They are also other types of diseases that
are not caused by pathogens and these are lifestyle diseases, things like heart disease
and lung cancer. Those things are caused by our environmental choices. For instances,
people who smoke are much bigger risk of lung cancer and so we have lifestyle and pathogenic
diseases.
As we learned previously about bacteria, they require these several things to grow: warmth,
food and water. Basically, bacteria grow by dividing and making copies of themselves.
What can happen is if you start off with one cell or a single bacteria that finds a food
source, that can then multiply and reproduce to produce two cells and then those two cells
reproduce each and they produce four, and so on to 8, 16, 32, 64 and so on. If we look,
this graph shows us the growth rate of a colony of bacteria. It shows that they are increasing
at an exponential rate. Exponential means this type of relationship here where it doubles
very, very quickly and so the numbers can increase rapidly.
In order for bacteria to grow, they need warmth, food and water. If any of those resources
run out, you get what is happening here where the growth rate slows down rapidly and then
it plateaus. Then, eventually what will happen is because of the lack of one of these three
resources, the number of bacteria tend to go down very, very rapidly. For instance,
if we look at a bacterial colony that might colonize some dead or some vegetable peelings,
then because they have adequate food source, their numbers will rise very, very quickly,
but as that food source begins to run out, the bacteria in numbers begin to drop very,
very rapidly because the resources run out.
In summary, diseases can be caused by microorganisms or lifestyle factors. In the case of lifestyle
factors, these diseases like heart disease or lung cancer. Of microorganisms, there are
three types, fungi being the largest, the next are bacteria and then the smallest are
the viruses.
Not all microorganisms are actually dangerous. Some of them are beneficial. But the ones
that do cause disease are referred to as pathogens. Once bacteria colonize a given area, then
they require three things: food, warmth and water. If any of those three things run out,
then the bacteria colony will reduce in size.
[end of audio – 05:07] A Level Biology: Microorganisms and Health
1 - Microorganisms Page…1