Class notes
BIOD 171 Chapter 1 Notes
- Course
- BIOD171 Microbiology
- Institution
- Geneva College
This is a comprehensive and detailed note on Chapter 1 for Biod 171. *Essential Study Material!!
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What is Microbiology?As the name suggests, it is the study of biological processes at the micro (microscopic)
level. These microorganisms usually consist of a single cell, so they are too small to
study with just your eyes. Examples would include bacteria, archaeons, fungi, protozoa,
and algae. Although they are also microscopic, viruses are not living, so they are not
considered microorganisms—a point that will be expanded later in this course.
However, viruses can be classified as microbes, a more general term that includes
microorganisms and viruses. Taken together, microbiology is the study of microbes.
Despite being invisible to the naked eye, microbes play a complex role in our world. For
instance, microbes can be beneficial in a variety of ways ranging from aiding in food
digestion to protecting us when we are exposed to potentially harmful foreign invaders
to helping crops grow. However, microbes can also be detrimental, as harmful strains of
bacteria, fungi, protozoa, and viruses kill millions of people each year and sicken even
more. Indeed, microbes can be just as harmful as they can be advantageous.
Although all four macromolecules described (proteins, nucleic acids, lipids and sugars)
exist in all living organisms, distinct differences in the organization of the cellular
materials are also possible. For this reason, not all organisms are classified in the same
way. The most common distinction between living organisms is to define whether their
cells are prokaryotic or eukaryotic. Prokaryotic is derived from Greek, meaning “before
kernel,” whereas eukaryotic means “true kernel.” The kernel described the appearance
of what is now called the nucleus of a cell—a membrane enclosed region within a cell
that contains the genetic material. Thus, prokaryotic cells lack a nucleus, whereas
eukaryotic cells have a defined nuclear region.
It is also important to simply note that as of 1990 biologists further expanded the
characterization and specification of the classifications of life into three
categories: Bacteria, Archaea, and Eukarya. The first two categories are all comprised
of prokaryotic microorganisms lacking a membrane-bound nucleus. The distinction
made between prokaryotes (Bacteria vs. Archaea) is based mainly on the differences in
cellular composition and is briefly described below. The Eukarya (eukaryotic)
classification remained unchanged and still consists of all nuclear-bound
microorganisms.
1. Bacteria
Bacteria (sometimes referred to as Eubacteria, meaning ‘true bacteria’) constitute a
large cohort of prokaryotic microorganisms. They can be considered the everyday
bacteria and are common in human daily life. They have a variety of shapes by which
they can be further classified.
Bacteria display many distinct morphologies (shapes), the most common
, include: coccus (round/spherical), bacillus (rod), vibrio (curved rod),
or spirillum (spiral/corkscrew).
Aside from the shape of the bacterial cell, consider the cellular organization—cells may
appear as isolated (individual) cells, in chains, or in clusters. Certain bacteria may also
demonstrate motility (swimming movements), while others do not. Examples of
Eubacteria are: Streptococcus, which have the appearance of round chains; E. coli,
which have the appearance of rod; and Mycobacterium tuberculosis, a unicellular
bacterium.
2. Archaea
Archaea , the other prokaryotic class of microorganisms, have similar characteristics
and shapes as Bacteria (Eubacteria) and yet remain genetically and compositionally
distinct. Most notably, they can survive in extremely harsh environmental conditions,
such as high salt levels, acid conditions, high temperatures, and oxygen-poor
conditions. As such, Archaeons may also be referred to as extremophiles, based on the
extreme or atypical environments in which they can be found.
3. Eukarya
Eukarya is a diverse category and consists of a wide range of microorganism. Due to
high diversity and complexity, eukaryotes can be subdivided into multiple categories, a
process still debated today. However, the unifying characteristic of all eukaryotic cells is
the presence of a membrane-bound nuclear region within the cell. For the purposes of
this course, eukaryotic microorganisms will be classified as
either: Animalia, Plantae, Fungi, and Protista .
Animalia consists of multicellular eukaryotic organisms, and, as the name suggests,
includes animals, as well as humans (and their cells) in their classification. All
microorganisms in this category are heterotrophic , meaning they are incapable of
producing their own energy, must absorb (consume) nutrients from the environment,
and have the general characteristic of motility (the ability to move).
Plantae are also multicellular eukaryotes, but, unlike Animalia, they can obtain most of
their energy from sunlight via photosynthesis—a process that converts light energy
(sunlight) into chemical energy (sugars) within the organism and fuels its activities.
Fungi can be either multicellular or unicellular microorganisms, and, like Animalia, they
are heterotrophic. A defining characteristic of fungi is the presence of chitin, a derivative
of glucose, in their cell walls. Common examples of multicellular fungi are molds and
mushrooms, while perhaps the most common unicellular fungus is yeast.
Protista are unicellular microorganisms that may form as colonies. However, the
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