A growth medium or culture medium is a liquid or gel designed to support the growth
of microorganisms or cells. There are different types of media for growing different types of
cells. There are two major types of growth media, those used for cell and microbiological
culture, which are used for growing microorganisms, such as bacteria or yeast. The most
common growth media for microorganisms is agar plates that are specialized media required for
microorganism and cell culture growth. Some organisms, termed fastidious organisms, require
specialized environments due to complex nutritional requirements.
For this experiment, an agar plate was used. An agar plate is a Petri dish that contains
a growth medium (typically agar plus nutrients) used to culture microorganisms. Selective
growth compounds may also be added to the media, such as antibiotics. Individual
microorganisms placed on the plate will grow into individual colonies, each a clone genetically
identical to the individual ancestor organism (except for the low, unavoidable rate of mutation).
Thus, the plate can be used either to estimate the concentration of organisms in a liquid culture or
a suitable dilution of that culture using a colony counter.
The first objective for this experiment is to study the growth of microorganism on agar
plates. We can observe the growth of microorganism after we place the agar plate at the different
place such as cafe, toilet, lift and drain. Secondly, to observe the characteristics of an individual
colony of bacteria growing on different types of agar plates which are nutrient agar, potato
dextrose agar and Mc conkey agar. Different types of microorganisms will produce different-
looking colonies, some colonies may be colored, some colonies are circular in shape, and others
are irregular. For characteristics, firstly, to observe the basic shape of the colony which are
circular, filamentous and etc. Secondly, to observe the size and diameter of the colony. Thirdly,
to observe the edge of a colony, the magnified shape of the edge of the colony. Fourthly, to
observe the surface of the colony appear and its opacity. Whereas it is transparent, opaque, or
translucent. Lastly, to observe the colour of the colony.
The materials that used for this experiment are prepared petri plates containing agar
medium and nutrients, incubator with 37 and container for the disposal of used plates.
The methods used are:
1. Each student was given three type of agar plates, which are nutrient agar, potato
dextrose agar and Mc conkey agar.
2. The cover of each the plates is opened and the agar is exposed for 15 second and 15
minutes at corridor near the cafe.
3. The cover is replaced on dish, tape closed, and each dish is labeled.
4. The petri dish is stored upside down in an incubator at 37 for 24 hours.
5. After 24 hours, the agar is taken out from incubator and the observation is made. The
record is made of what we saw growing in each dish.
6. After finish the observation, the plate is dispose in the yellow bin near the incubator.
The hand must be wash with soap before leave the lab.
The results for all plates that requires 15 seconds exposure is the same which is there is no
microbial growth found. Only plates with exposure of 15 minutes are found to have microbial
growth such as below:
Agar Plate Form Size Elavation Opacity Color
Nutrient agar Circular and 0.3 cm Raised and Opaque White
Potato Circular and 0.3 cm Raised and Opaque White and
dextrose agar filamentous convex black
Mac Conkey Circular, 0.3 cm Raised, Opaque Purple
agar irregular and convex and
We should examine cultures in petri plates, which have been taped and closed. Colony
morphology is a method that scientists use to describe the characteristics of an individual colony
bacteria growing on agar in a Petri dish. It can be used to identify them. A specific terminology
is used to describe common colony types.
The agar plates were exposed at cafe for 15 second and 15 minute. For agar plate A that
is exposed for 15 second, there has no microorganism had found. The agar plate is clean. But for
agar plate B, it is different. There has a colony on an agar plate. The colony has their own
The form of colony is circular. It is circle shape on agar plate. The size and diameter of
the colony is 0.4 cm. It is so small. Tiny colonies are referred to as punctiform. When turn the
petri dish on end, the side view of a colony is flat. The magnified shape of the edge of the colony
is entire. The surfaces of the colony appear is smooth. While its opacity is transparent that is
clear. It can look through frosted glass. We can see it clear when we look it under light. Lastly,
the colour of the colony is white. We can know the level of cleanliness at cafe according to the
characteristics of colony.
Microorganism exists at all place but we are not concerned about that. According to the
result that I got from cafe, this shows at cafe also has microorganism but in medium level. This
shows because the diameter of colony is 0.4 cm and the colour of colony is white. This
experiment has relationship with Pasteur experiment. Pasteur experiment discoveries that
microorganisms present in non living matter. His experiment showed that microorganisms come
only from other microorganisms and that a genuinely sterile solution remains lifeless unless
contaminated by living creatures. This showed when the agar plate is exposed for 15 minute, the
colony exists is more than agar plate which is exposed for 15 second. This means microorganism
present in non living matter.