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Introduction to the Microbial World

November 24, 2019

Hey, it’s Professor Dave, let’s check
out some microbes. If you’re a living, breathing human being,
you’ve probably come down with a cold at some point in your life. Maybe you’ve suffered from food poisoning,
or chickenpox, or taken antibiotics for an infection. But have you ever wondered what causes these diseases? What’s going on inside the body? It turns out that there’s an incredibly
diverse world of microscopic organisms that exist virtually everywhere you can imagine. They’re living right on our skin, they’re
lurking in deep sea hydrothermal vents, they’re in the soil in our gardens, on doorknobs,
in our mouths and stomachs, and even in the air that surrounds us. That may sound a little alarming, but don’t
worry, most of these microscopic organisms are quite harmless. Many of them are even helping you survive
right now, by protecting your skin, airways, and digestive system from foreign invaders,
which are known as pathogens, and these are the little critters that will be the main
focus of this series, so let’s dive right in. Humans have been getting diseases from pathogens
since there have been humans, but it wasn’t until we developed the technology to see incredibly
small objects that we began to fully understand the world around us. It all began with a Dutch father-son team
named Hans and Zacharias Janssen, who invented the first compound microscope in the late
16th century. Their device, which was essentially a tube
with a lens at the top and bottom, magnified objects somewhere between three times and
nine times. The images were pretty blurry, but their invention
laid down crucial groundwork for researchers to come. Over a hundred years later, in the late 1600s,
technology advanced such that the microscope could magnify objects up to 270 times. Enter Anton van Leeuwenhoek in 1674, a cloth
merchant-turned-biologist who worked to improve the microscope so that he could see his wares,
which was the cloth he sold, up close and personal. Imagine his surprise when he accidentally
discovered bacteria! As he peered through his microscope, he noticed
a new world, millions of what he called “animalcules” in a single drop of water. Once we could see these things, scientists
began to slowly examine and classify the tiny organisms that are all around us. Almost a hundred years after Leeuwenhoek’s
discovery, Danish biologist Otto Müller developed a system to organize bacteria into categories,
which we will get to a bit later. Nearly a hundred years after that, in 1840,
German pathologist Friedrich Henle proposed a series of criteria to prove that microorganisms
cause human disease, and this was called the “germ theory”. Louis Pasteur and Robert Koch confirmed Henle’s
theory in the 1870s and 1880s, demonstrating with a series of involved experiments that
microorganisms are responsible for causing diseases such as cholera, the plague, tuberculosis,
and rabies. The world that Leeuwenhoek discovered was
both exciting and mysterious, harboring creatures of all shapes and sizes, of mysterious origin
and unknown purpose. And now in the 21st century, we know that
there are literally thousands of types of microorganisms living around us, on us, and in us. To understand how microorganisms cause disease,
it’s helpful to understand the similarities and differences among them, and the categories
they fall into, so we will need to understand this before we look at individual diseases. Microbes can be divided into four distinct groups. Those are viruses, bacteria, fungi, and parasites. Viruses are the smallest of these infectious
agents, ranging from 18 to 300 nanometers in diameter. For the most part, they can’t be seen with
a light microscope, which is the regular kind most people are familiar with, which uses
visible light and magnifying lenses. More powerful microscopy techniques are required. With these, scientists have discovered over
100 families and 2,800 species of viruses, and that number rises every year. Of course, not all viruses can infect humans,
so we don’t need to get overly anxious. For more information on viruses, check out
this tutorial in my biology series. This should be enough to understand what we
will discuss about viruses throughout this series. Next up is bacteria. These are quite different from viruses, in
that they are what we call prokaryotic organisms, which means that they are unicellular in nature. Viruses are not made of cells, and are much
smaller than even a single cell, so bacteria, even with just the one cell, are dramatically
more complicated than viruses, whose status as living organisms is actually quite ambiguous. Bacteria can be classified based on their
shape, which can be spheres, rods, or spirals. They can be classified by their size, typically
between one and twenty micrometers, which are millionths of a meter. And they can also be classified by the way
that they’re arranged, which can be as single isolated cells, in chains, or in clusters of cells. To go a little deeper, bacteria can be further
classified by the genes they contain, which we call genotypic properties, as well as the
observable characteristics they display, which we call phenotypic properties. Just as with viruses, we did cover a reasonable
amount of information regarding bacteria in the biology series, so feel free to check
out this tutorial now if you’re rusty on the prerequisites. Next up, fungi are even more complex than bacteria. Fungi are eukaryotic, which means the cells
that comprise them contain a nucleus, endoplasmic reticulum, Golgi bodies, and mitochondria,
unlike bacteria, which do not have these organelles and other complex features. Fungi sometimes exist in a unicellular form
called yeast, that can replicate asexually, or in a filamentous form called mold, that
can replicate sexually or asexually. Lastly, parasites are the most complex microorganisms. Some parasites are unicellular, while others
are multicellular. Their life cycles can vary drastically, depending
on the type of relationship they form with their host. Parasites can range in size from a diameter
of one micrometer all the way up to ten meters in length. So that is a brief introduction to the types
of microorganisms we will be discussing throughout this series. We’ve learned a bit about them already in
biology, but now that we have learned all about the human body in the anatomy and physiology
series, we are ready to learn about how pathogens interact with our bodies to make us sick. So let’s move forward and begin to do just that.


  • Reply Sunny Buddy November 18, 2019 at 5:34 pm


  • Reply Ayad Ali November 18, 2019 at 5:36 pm


  • Reply khalil hadi November 18, 2019 at 5:36 pm

    Thank you alot

  • Reply JASON RKO JASON RKO November 18, 2019 at 5:36 pm


  • Reply Brainstorming Plus November 18, 2019 at 5:38 pm


  • Reply REDNECK Rootz November 18, 2019 at 5:41 pm

    Love your videos I learn so much thanx

  • Reply Beyzanur Yıldırımyılmaz November 18, 2019 at 5:56 pm

    Thanks again for the lesson~ Could you maybe make a video about RNA types and splicing kind of things, sometime when you have time? I couldn't find any about them in your channel, are there any?

  • Reply Ivan Rogic November 18, 2019 at 5:58 pm

    Thank you!

  • Reply Ibrahim Eldeeb November 18, 2019 at 6:14 pm

    رائع جدا

  • Reply Dexter Neustadt November 18, 2019 at 7:41 pm

    You're the only guy I know who looks good with long hair, and with short hair.

  • Reply memo boy November 18, 2019 at 9:54 pm


  • Reply Conscious Robot November 19, 2019 at 12:56 am

    Can you imagine being the first person to discover that there are tiny little creatures we can't see all around, on us, and in us? That would freak me the hell out.

  • Reply Aya Sykes November 19, 2019 at 9:20 am

    Daddy Dave explains

  • Reply Chandrapaul Ghosh November 24, 2019 at 3:09 pm

    congrats on your new shirt

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