P4 work and achieve 2 main goals. The


P4 – Part C – Growth of



that influence growth of micro-organisms:

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The Temperature, PH, osmotic pressure, hydrostatic pressure
and radiation all influence the growth of a microorganism. To grow a
microorganism water is the essential element.


Nutrients like Carbon , oxygen , hydrogen , nitrogen , sulfur
, phosphorus , potassium are needed to help an microorganism to grow. They also
need a variety of materials to work and achieve 2 main goals. The first goal is
to make sure they have enough energy to grow and the second goal is to repair
themselves by extracting building blocks to multiply.  In some particular environments,
micro-organisms can grow better. This depends on environments with an even
amount of elements being distributed in order for the microorganism to grow
properly. Water is necessary for a microbe. Inorganic compounds give energy and
nutrients to chemoautotrophic and photoautotrophic microbes. Photoautotrophs
use photosynthesis to do so and chemoautotrophs do this through chemical


In aerobic conditions it is free of oxygen. For cellular
respiration aerobic bacteria uses oxygen. For energy yielding properties oxygen
is required for aerobic organisms.


This Lacks oxygen. Anaerobic bacteria can grow without
oxygen, this is due to the gases that the bacteria can produce because of their
metabolism. The gases they give off are odoriferous gases like hydrogen
sulphide and methane. Clostridium is an example of a certain pathogenic specie
that is an anaerobic bacterium. The bacteria that grows in low oxygen
environments has to have a high concentration of CO2, are microaerophilic. 



If there is an increase in temperature, there is an increase
in enzyme activity. When proteins are within their proper conformations
bacteria can survive. Enzymes are also proteins. For an enzyme to work properly
they have to have the right optimum temperature. An enzyme can become inactive
or will not function properly if the optimum temperature increases. This could
be because the enzyme can’t function properly without their specific
temperature making the bacteria die. The bacteria’s cell wall that helps
protect it can be affected due to the change of the temperature. Which could be
another reason for why a microorganism can die and stop growing. Psychrophilic
organisms, mesophilic organism and thermophilic organisms have preferred temperatures
at which they grow at. For example, the psychrophilic organisms grow at temperatures
at around 0-20 degrees Celsius. mesophilic organisms grow around 20-40 degrees Celsius
and the thermophilic organisms grow higher than 40 degrees Celsius.




It is a number that expresses how acidic or how much alkaline
there is in a solution, on a scale. The oldest kind of living organism on
planet earth is bacteria. They are essential for life although they can cause
diseases. A certain PH balance is preferred for a bacterium. If there is a
change of the OH kevel then they hydrogen ions are either added or subtracted. The
optimum PH for most bacteria is around 6.5-7.5. For human tissue the PH lies
around 7.0 – 7.2. In the body, the neutrophilic bacteria grow well. Acidophilic
are bacteria’s that have a PH level of 6.0 or below. For example, moulds and



When the salt in the saline solution dries up and is left
behind, it subjects to osmotic potential. If there is no moisture it could
limit the microbial growth in different environments. The enzyme’s activity can
be lowered because there is not enough hydration due to there not being enough
water available which inhibits microbial activity, in addition it lowers the
intracellular water potential. For the culture medium the correct osmotic pressure
is essential. Hypotonic means a solution that is diluted with a high
concentration of water within the cell. The microbe will gain more water if the
medium is hypotonic, through osmosis. Hypertonic means there is a low
concentration of water in a solution within the cell. Therefore, if the medium
is hypertonic the cell loses water by osmosis. If a microbe cell is shrivelled
up this means that the solute concentration was higher than its own cell when it
was placed into the solution. However, when put into a solution with a lower concentration
of solutes, than the microbe itself will get larger and burst.



Is when you are exposed to radiation, for example natural
sources. Irradiation is used on food so that it eliminates microorganisms that
causes disease. Ionising radiation is an example of irradiation. Ionising
radiation uses high intensity and short wavelengths for sterilising to destroy
microorganisms. Gamma irradiation, x ray radiation and electron irradiations
are all forms of ionizing radiation that is used to sterilise.




They kill bacteria and treat bacterial infections. These are antimicrobial
drugs that are used to eliminate bacterial infections so that they are
prevented from spreading. Antibiotics do not eliminate viruses.



These are used to treat fungal infections that are usually
found on skin, hair and nails. Fungi feed on broken down tissues and are plant
like organisms. They are chemicals that kill or stop the fungal cells from
growing by treating the infection. The cell wall of a fungi is affected by the
antifungal medicine making the wall leak and all of its fungal contents till it
dies. This stops fungal cells from reproducing and growing any further.



These are powerful medicines that are used to help fight off
bacterial infections. Viruses can cause infections like the flu. Viruses are
prevented by antivirals. They are required when fighting off infections. Viral
pathogens are attacked by the antivirals as it helps boost the immune system. However,
pathogens are starting to mutate over the time which makes antivirals harder to
fight the virus. Antiviral drugs are used to interfere with the infections of
viruses so that they don’t reproduce by infecting a host cell. The way this
happens, is by the antiviral blocking the virus from getting to the host cell
and by stopping the virus from releasing and copying its genetic material into
the host cells DNA.



Disinfecting is the process of cleaning something with
chemicals to stop the microorganism from growing This happens by the
disinfectant destroying the microorganisms. However, they don’t always kill all
the microorganisms that are present. But do however lower the number of
microorganisms so it is less dangerous. Disinfectant is toxic to the human body
which is why it is not consumed by the human body, but is however sprayed
around table tops and other non-living objects to get rid of microorganisms. Antiseptics
however can be used on the living tissue.



Kills bacteria and helps stop the growth of bacteria.
Sterilisation is used widely in the microbiology lad. By steaming as a way of
sterilising it is cheap and not toxic. The affect it has on materials stops it
from being contaminated. To sterilise you can use:

Steam to heat the material by killing the spores or microbes
found on the material this is also known as autoclaving.

By oxidising the cellular components of a microbe it can kill
them which need much more energy than hydrolysis of proteins. However for
efficient sterilising of dry heating, a lot of high temperature is needed.

By using disinfectants in solvents, you can denature the
proteins that require water for the process making it effective.

By using radiation, it can damage the DNA of a microbe found
on a material making it a useful tool to sterilise. The forms that are commonly
uses are x-rays and gamma rays.

























My scientific investigation:

I tested to see if different PH levels in petri dishes
affected the growth rate of a bacterium that was used. The PH levels was 4, 7
and 10.Lower than the neutral level (acidic) , 7 which is the neutral level and
one alkaline. The bacterium I used throughout was E coli.

I used aseptic techniques to prevent and minimise
contamination. I did this by sterilising the equipment before and after use. This
was done when I did the streaking of the E-coli bacterium with the inoculating
loop on to my petri dish. Before doing this, I sterilised it under a Bunsen
burner to get rid of impurities and potential pathogens from affecting my
results. I also did this after streaking the plate. I sterilised the bottle
neck of the E-coli so that I was preventing and eliminate contamination.

I added the bacterium in to all 3 petri dishes and then
placed it in the same environment to check them every week to see the growth of
the microbe. The temperature of the environment I left it in was around room


The independent variable I used was the bacterium I was using
to streak in the 3 different PH petri dishes.

The dependent variable was the petri dishes all being from
different PH’s one being acidic , neutral and an alkaline.         

The control variable was the environment I stored my petri
dishes in , to see if any bacteria culture had grew. However, this experiment
didn’t show much changes in the results. The petri dishes with the PH of
7(neutral) had no changes or observations of bacterial growth. The petri dish
with the PH of 4 also had no signs of bacteria growth however the petri dish of
PH 10 had a pink dot that grew which indicates the growth of bacteria.



I had observed to see if there were any bacteria that grew on
the petri dishes. Unfortunately, there wasn’t much that grew accept on the PH 10,
there was a pink dot.









M3 – Part C



Serial dilution:

When there are too many microorganisms to count serial
dilution is used to take a sample which contains the microorganisms in a
standard solution being diluted a few times. Each time 1ml of the diluted
solution previously is added to 9ml of distilled water. This is repeated more than
once. There will a be a lot of microorganisms in one of the samples and in the
other sample there will be 5-10 colonies all depending on each samples

Viable counts:

To work out how much actively growing cells are in a sample,
the viable cell count is used. on a nutrient medium a colony of bacteria grows
which makes the spread play rely on it. This makes the colony look visible
which means they can be counted easily on 
the pate. The original samples dilution has to be messed about with till
it gets to an average of 30-300 colonies to grow the targeted bacterium.
Several dilutions become cultured so that there is a suitable amount of
colonies that are generated. Serial dilutions are made in a lab procedure in
sterile water in ratios like 1:10 and 1:100. 
They also have to be cultivated on a agar dish containing nutrients and
then are sealed and left in an incubator. For 24 hours the first set of plates
is incubated at 22 degrees Celsius ad then in the second set for 24 hours they
are incubated at around 37 degrees Celsius. To easily identify the target
organism agents are included in the composition of the nutrient which makes the
growth of the non-target organism resist from being grown. To identify the
target organisms there is normally a colour change found in the medium.

Total counts:

To measure how much bacteria or east is present a total count
is carried out to get a measurable idea. It is measured in ml or g to represent
how much CFU is in the sample. The colony count is also known as the total
count, this is because it provides how mych microbes there are which are viable
and not viable. Bacteria, yeast and other cells are all counted. The pour plate
meth id carried out as well as looking through a microscope to get a total

If you look at how much microbes there are in water the pour
plate method is used.:

On several plates the method to identify the water volume
that has yeas-malt in which extracts the agar and sets for an amount of time.

For 24 hours one set of plates is incubated at around 37
degrees Celsius. Between 20-22 degrees the rest of the plates are incubated at
around that temperature.

Water makes bacteria grow well at around 22 degrees Celsius.
If there are microbes that don’t grow around 37 degrees Celsius then they won’t
grow as better as a microbe that is in water.

Growth patterns can be different for different microorganisms
which needs to be counted. So to make it more clearer and more useful the different
microorganisms are counted in water to evaluate how effective the water
procedure is to treat the microorganism. An example of the water procedure that
can be used is disinfectants.

Microbiological assays:

To measure compounds the microbiologic assay method is used
on microorganisms to measure vitamins or amino acids. The factor that is under
examination becomes excluded to the organism that is inoculated into a medium
containing the growth factors that are essential. How much nutrients were added
to the substance relates to the growth rate of the organism.

Dry mass determination growth of mycelial discs viral plaque
counts (liquid or solid media):

Using materials like an oven or another dry mass technique,
kills microbes to a certain extent in a warm environment. When the microbes are
left from the microbe that has dried up completely, the amount of micro that is
present is then measured.

To decide how much microbes there will be in a sample it is
determined by a dry mass determination where the weight of the cell is measured.

This includes examples like:

When the water content is removed from a dry sample it is
weighed out this method is called the gravimeter method.

When there is a loss of intense transmitted light because of
the particles that are scattered to it Is measured. The light wavelength that
passes through the filter passes through the cuvette containing a solution.
This is using the turbidometry process.

Process of the growth of mycelial discs:

Mycelial growth is affected by factors like the PH,
temperature , carbon and nitrogen sources. The best growth mycelial growth was
to have a PH of 5.5, the temperature of 20-25 degrees Celsius, to have carbon
sources like glucose or nitrogen.

Use of colourimetry to determine turbidity in liquid media:

A sample of liquid can be measured to see how much particles
are suspended in it by looking at how much light can pass through it. Looking
at a sample of water light can pass straight through which means that the water
is clear. If there is sand in the water, then the particles will scatter the
light from passing through or it can make the water less clear by appearing
cloudy. This therefore means that cloudy water is more turbid than clear water.
By looking at cell density and culture sample these can also be used to determine
their turbidity. The higher the turbidity the more cells appear.


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