Microbiology, part 2: Foundations - Overview of Microorganisms


Cathy reviews the three domain system used to classify organisms and the key differences between prokaryotes and eukaryotes. She also provides an overview of the following microorganisms: bacteria, archaea, protozoa, algae, parasites, fungi, and viruses.

At the end of the video, Cathy provides a quiz to test your understanding of some of the key facts she covered in the video.

Our microbiology video tutorial series is taught by Cathy Parkes BSN, RN, CWCN, PHN and intended to help RN & PN nursing students, pre-med and health care / biology related programs study for school exams, TEAS exam, and the HESI A2 Exam

  • 00:00 Intro
  • 1:11 Classification of Organisms
  • 2:52 Prokaryotes vs. Eukaryotes
  • 4:12 Bacteria
  • 5:07 Archaea
  • 5:51 Protozoa
  • 7:00 Algae
  • 7:33 Parasites
  • 8:36 Fungi
  • 9:57 Viruses
  • 10:42 Quiz Time!

Full Transcript: Microbiology, part 2: Foundations - Overview of Microorganisms

Hi, I'm Cathy with Level Up RN. In this video, I will be providing an overview of microorganisms.

Specifically, I'll be talking about the three-domain system for classifying organisms. I'll be talking about the key differences between prokaryotes and eukaryotes. And then I'll be discussing the key attributes of bacteria, archaea, protozoa, algae, parasites, fungi, and viruses.

So in this video playlist, we will be going into a lot more detail about bacteria and viruses.

This particular video is really meant to be a high-level overview to help set the stage for the videos that follow.

At the end of the video, I'm going to give you guys a quiz to test your understanding of some of the key facts I'll be covering, so definitely stay tuned for that.

And if you have our Level Up RN Microbiology Flashcards, definitely pull those out so you can follow along with me in this video, and pay close attention to the bold, red text on the back of the flashcards because those are the things that you are likely to see show up on a micro exam.

The three-domain system is used to classify organisms based on their cell's RNA, cell membrane structure, and sensitivity to antibiotics, and there are three main domains of life. This includes bacteria, archaea, and eukarya.

So organisms in the bacteria domain are all prokaryotes, which means that their DNA is not enclosed in a nuclear membrane. In addition, their cell walls contain peptidoglycan, which is a structure made up of sugars and amino acids.

Organisms in the archaea domain are also prokaryotes, but their cell walls do not contain peptidoglycan.

Organisms that fall within the eukaryote domain are all eukaryotes, which means that their DNA is enclosed in a nuclear membrane. Not all eukaryote have a cell wall, but for those that do, it does not contain peptidoglycan.

Examples of eukaryotes include plants, animals, fungi, protozoa, algae, and parasites.

So outside of these three domains, we also have acellular infectious agents, which are technically not considered organisms. So acellular means not composed of cells. So anytime you see "a" or "an", followed by another word, that means without the thing that follows. So examples of acellular infectious agents include viruses, viroids, and prions.

Let's now go over some key differences between prokaryote and eukaryote cells that you definitely have to know for your micro class.

So in terms of size, prokaryotic cells are much smaller, often between 0.2 and 2 micrometers, whereas eukaryote cells are larger, often between 10 and 100 micrometers.

As I mentioned before, the DNA in prokaryote cells is not contained in a nuclear membrane. Instead, prokaryotic cells contain a single circular chromosome, which is located in the nucleoid region of the cell.

By contrast, the DNA in eukaryote cells is contained in multiple linear chromosomes, and these chromosomes are located in the nucleus of the cell, which is enclosed in a nuclear membrane.

Other key differences between these two types of cells is the fact that prokaryotes do not contain any organelles, whereas eukaryote cells contain various organelles such as mitochondria and lysosomes, for example. In addition, prokaryotes will divide via binary fission, whereas eukaryotes cells will divide via mitosis.

Let's now go over some of the key attributes of microorganisms that I mentioned earlier, starting with bacteria.

So bacteria are unicellular prokaryotes. So unicellular means composed of one cell. As I mentioned earlier, bacterial cell walls contain peptidoglycan, and bacterial cells will divide via binary fission.

Most bacteria are harmless, but some may be pathogenic, which means that they can cause disease.

Some bacteria are photosynthetic, which means they have the ability to convert sunlight into chemical energy, whereas others are not.

Some bacteria will have flagella, as shown here in this image, which are long, whip-like structures that help to propel the cell forward, whereas some bacteria lack flagella.

Next, let's talk about archaea. So archaea, like bacteria, are unicellular prokaryotes, but their cell walls do not contain peptidoglycan.

Archaea are not harmful to humans, and they are able to live in extreme environments.

So for example, methanogens are a type of archaea that are able to survive in anaerobic environments, so environments that lack oxygen, and they produce methane as a byproduct of their metabolism.

Other examples include halophiles, which are able to live in extremely salty environments, and thermophiles, which are able to survive in extremely hot environments.

Next, let's talk about protozoa, which are unicellular eukaryotes. So protozoa can reproduce asexually, such as through binary fission, but some protozoa can reproduce sexually as well.

Some protozoa are free-living, whereas others are parasitic, and some protozoa are pathogenic to humans.

So the protozoa shown in the image on the screen is giardia, which is a parasitic protozoan that causes diarrhea in humans.

Most protozoa are non-photosynthetic, and they can move using pseudopods, flagella, or cilia.

So pseudopods are referred to as false feet. This is where the protozoan extends part of their cell membrane and cytoplasm to kind of move themselves forward.

Flagella, as I mentioned before, are long, whip-like structures.

Cilia are hair-like structures that are similar to flagella, but they're shorter, and they are located all over the cell.

Next, let's talk about algae, which are unicellular or multicellular eukaryotes. They can reproduce sexually as well as asexually.

Their cell walls are composed of cellulose, which is a polysaccharide made up of sugar molecules.

They live in aquatic environments, and most algae is photosynthetic.

Most algae is not harmful to humans, but some algae, such as blue-green algae, can produce a toxin under certain environmental conditions.

Next, let's talk about parasites, which are eukaryotes that can be unicellular or multicellular.

The most important thing to remember about parasites is that they rely on other organisms for their nutritional needs.

The three main types of parasites that cause disease in humans include helminths, protozoa, which we talked about before, and ectoparasites.

So helminths are large, multicellular endoparasites. So endo- means inside. So these types of parasites are going to live inside their hosts.

Examples of helminths include roundworms and flatworms.

Ectoparasites, on the other hand, live outside their hosts. So ecto- means outside. These type of parasites typically like to attach or burrow into the skin.

Examples of ectoparasites include ticks, fleas, lice, and mites.

Next up, we have fungi, which are eukaryotes that can be unicellular or multicellular. Their cell walls are composed of chitin, which is a polysaccharide made up of sugar molecules.

Fungi can reproduce sexually or asexually, and they are non-photosynthetic.

There are three main types of fungi, which includes yeast, mold, and dimorphic fungi.

Yeast are unicellular, and many yeast are beneficial, such as those used to ferment alcoholic beverages, but some are pathogenic, such as candida, which can cause a vaginal yeast infection.

Unlike yeast, mold is multicellular, and it is made up of long filaments called hyphae that form colonies called mycelia.

So molds can produce toxins, which can cause allergies and disease, but some mold is beneficial, such as the mold used to make penicillin.

And then lastly, we have dimorphic fungi. This type of fungus grows as a mold in colder temperatures, but grows as a yeast in warmer temperatures. So our Cool Chicken Hint to help you remember these two forms is mold in the cold, yeast in the heat.

Lastly, let's touch briefly on viruses, which we will be talking a lot more about in this playlist, but I wanted to do a little overview like I did for the other microorganisms.

So viruses are acellular, meaning they are not composed of cells. They consist of DNA or RNA, not both, surrounded by a protein coat.

So viruses are obligate intracellular parasites, which means they can only reproduce when they are within a host cell. So they are inert outside of a living host, so they basically need to invade a cell and hijack the cellular machinery in order to reproduce.

All right. It's quiz time. In this quiz, I am going to describe a microorganism or other thing that we might have just talked about, and you are going to name that microorganism. Are you guys ready? All right. Here we go.


This eukaryote has a cell wall composed of chitin and is non-photosynthetic.

The answer is...fungi.

Number two.

This unicellular prokaryote has a cell wall that contains peptidoglycan.

The answer is...bacteria.

Number three.

This eukaryote has a cell wall composed of cellulose and is photosynthetic.

The answer is...algae.

Number four.

This is a unicellular prokaryote that is able to live in extreme environments, and whose cell wall lacks peptidoglycan.

The answer is...archaea.

Number five.

This is an acellular infectious agent that consists of DNA or RNA surrounded by a protein coat.

The answer is...virus.

All right. I hope you did great with that quiz, and I hope you found this video to be helpful. Take care, and thank you so much for watching.


And thermophiles, which are able to-- to antibiotics. And there are three. Three, not four. I don't know. My pinky wanted to get in there. Contain peptidoglycan and-- ooh, baby.

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