Unit 17AB: Microbiology and Microbiological Techniques
What are microorganisms?
Introduction to Microorganisms
Bacteria
(https://byjus.com/question-answer/what-is-meant-by-characteristics-of-bacterial-cells/).
(https://biologydictionary.net/binary-fission/).
This is a single-celled (unicellular) prokaryotic organism and belongs to the Monera kingdom in
the living things classification. They are also known as “eubacteria” or “true bacteria”. The
typical size of a bacteria is between 0.5µm to 1µm, these bacteria cells can then be viewed under
a microscope and can have three unique shapes – Bacilli (rod-shaped), Cocci (sphere-shaped)
and Spirilli (spiral-shaped). The bacteria cell has many different characteristics. Each bacteria
cell consists of a cell wall which helps to provide support and protect the bacteria cell from the
environment. A protein-sugar (polysaccharide) molecule – peptidoglycan. This is useful as it
helps to prevent the cell from bursting especially when the pressure between the cytoplasm and
environment are significantly different. The bacteria do not contain a nucleus but instead have a
DNA loop that loosely flows and is called a nucleoid or plasmid DNA. Data is stored within the
RNA ribosomal and assemble protein that are made from specific amino acids. The flagella also
help the bacteria to move easily and to attach itself to a host. Bacteria cells rely on binary fission
to propagate. It starts of with the DNA unravelling itself, these strands of unravelled plasmids
will then be replicated by proteins which have been specialised and will also duplicate the
plasmids. Once both the DNA and plasmids have been duplicated they will attach themselves to
2 separate sides of the cell membrane – this will happen whilst the cell prepares itself for the
division process. After this, both the cell wall and membrane will start to break off and form two
new cells and finally once the two cells have fully separated, any additional proteins or molecules
will also break up and form within the new cells. Some bacteria are also pathogenic meaning
they can spread from one organism to another – this could be from things such as the air, food or
close contract through touch.
,Fungi
Fungi can either be unicellular (single celled that contain cell plasma
membrane organelles) like yeast, or multicellular organisms (have
more than one cell) like mushrooms. These are eukaryotic cells and
due to the cell wall being composed of chitin are labelled as fungi
which differs to the cellulose that makes up the cell wall of a plant.
Fungi is split in 3 major groups: mushrooms/toadstools, yeast and
moulds, they are separated into these groups based upon their life
cycle and the arrangement of their spores. Fungi tends to be varied in
size due to there being lots of different groups. Usually the most
microscopic fungi are about 2-10µm, with the average size of a fungi
being 5-50µm in length. Fungi are able to absorb nutrients and organic
material from the environment (heterotrophs) as well as some fungi
being able to produce enzymes that turn dead organic matter into
chemicals which the fungi will then use for food. Fungi can
reproduce both asexually (does not involve the fusion of gametes)
these require mitotic spores and sexually (requires the fusion of the
male and female sex cells) these require meiotic spores. Most fungi
reproduce asexually and this is thanks to the formation of spores.
These spores spread by the wind due to them being very small and
light with them then being able to be transported to a new
environment and grow there. However, some fungi can reproduce
sexually. They often do this by merging together their hyphae, this
will then go into an interconnected network called anastomosis. The process starts when two
fungal organism’s haploid hyphae join together. The cytoplasm from both of these organisms
merge together but the nuclei does not. The hyphae produce a dikaryon – two diploid nuclei. The
dikaryon will then get the nuclei to fuse together with sexual sporangia – here the two diploid
nuclei will fuse into one. Finally, meiosis is undergone to form haploid spores and the process is
then repeated.
Yeast: The size of yeast averages 3-4µm with the largest being 40µm. These are multicellular
organisms which don’t produce hyphae. Sugar found on fruiting plant and nectar in flowers
serve as food for “wild” yeast. These “wild” yeast then can be used for making bread and the
fermentation to help produce alcoholic beverages. Yeast reproduces asexually – they usually
divide through mitosis.
Protozoa
A protozoa is a single-celled, eukaryotic microorganism
that comes in the form of many different shapes and sizes.
It is heterotrophic – meaning it uses organic carbon as its
primary source of energy. Its natural habitat is in fresh
water, marine environments and the soil. The size of the
, microorganism can range from 1µm to 2mm. The protozoa have a flagellum to help it move
around easily. This microorganism lacks a cell wall to
reduce the rigidness of the cell, with this being allowed
to happen it will allow the cell to become more flexible
and this results in the protozoa’s shape being more
varied. We have discussed that the protozoa have a
range of shapes it can adopt due to the cell wall being
less rigid. However, the protozoan cell morphology and
motility are split into the basics of 4 major types:
Flagellates, Amoebae, ciliates and Spore-forming
protozoa. As I stated previously, the protozoa are motile,
it can move by other means as well not only with the
help of the flagella. The cilia have tiny hairs that beat at
a regular pattern, this pattern will allow the cell to move
– the behave like oars on a boat. Additionally, amoeboid
movement will also help the cell move around, it works
by sending out pseudopodia, temporary protrusions – these fill the cytoplasm and will allow
movement of the microorganism. The most common method the reproduction for protozoa is by
asexual binary fission, the mother cell will split into two identical daughter cells which will
continue repeatedly. The protozoa can sometimes also reproduce sexually with the Ciliophora
undergoing conjugation.
Viruses
This is an infection cell that can only sustain itself and multiply in a host cell by reprogramming
the nucleus to make more viruses until the cell fills up and bursts and the viruses move on. The
virus is the smallest microbe on this list ranging from 20nm – 500nm. The main composite of a
virus is the nucleic acid – this is surrounded by a protein coat named capsid. This can be
structured from either DNA or RNA but will never be both. The virus has both living and non-
living characteristics – it can infect plant, animal and other microorganisms.
Living Characteristics of Viruses Non-living Characteristics of Viruses
The virus can mutate – whilst the virus The virus is acellular – meaning they have no
replicates itself, the genes undergo random cytoplasm or cellular organelles. This like
“copying errors” – this can allow the virus to living viruses means they can only replicate
change its surface proteins and antigens and survive within a host’s cell.
which will not allow the immune system to
detect the virus as it won’t be able to
recognize and fight the virus.
Due to the viruses not possessing ribosomes, Similarly, to the living virus, it contains either
this will mean it cannot form proteins DNA or RNA but cannot have both.
independently, this will mean that the virus
will not be able to reproduce outside the
hosts’ cells.
Viruses (once inside a host cell) can replicate Due to it not having any cytoplasm or cellular
rapidly due to it being able to “Cell Surface” organelles it produces zero waste and energy.
this means that it can surface from cell to cell It cannot grow or metabolise either.
