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MCAT
History and development of cell theory
Created by Matthew McPheeters.
Want to join the conversation?
- What is the difference between the first two points of cell theory? They sound the same to me.(7 votes)
- They do kind of sound similar. But one says all living things are made of cells, meaning that all living things must have cells. And the 2nd says cell is the basic function unit, meaning that the cell is the smallest thing that can be alive. If you break a cell apart, there is no life beyond that point. But a cell can survive on its own (not all cells can but you get the idea)(9 votes)
- It should also be noted that there is a "fourth tenet" that is often referred to when discussing cell theory. This is that genetic information is stored in the form of DNA and can be passed down to offspring.(9 votes)
- Thank you for the information!
Can you point me towards where you found this information so I may research it?(2 votes)
- Is the history portion high yield for mcat?(1 vote)
- According to the Kaplan MCAT books, it is not just focus on the tenents overall.(2 votes)
- why the cells in the pastuer experiment with a curve in the tube were not able to retain characters of life?(0 votes)
- Boiling of the broth kills all bacteria in the fluid since the microorganisms cannot handle the high heat. With a normal flask, particles containing microorganism were introduced into the broth when they fell into the flask.
In Pastuer's experiment, he created a flask with a long neck so that nothing would fall into the flask. So once he heated the broth killing the bacteria, the broth would remain sterile since microorganisms could no longer "fall" into the flask.(4 votes)
- How does the swan neck bottle fit in with it all?(1 vote)
- do we have to learn the modern cell theory??(1 vote)
- Are their cells all over your body or in only some places?/(1 vote)
- Yeah there are cells all over your body in every place(1 vote)
- Hearing him mispronounce Latin is cringe-inducing.(0 votes)
- If nucleus of the cell is acidic in nature and cytoplasm is basic in nature then why there is no neutralization reaction between nucleoplasm and cytoplasm during cell division when there is no nuclear membrane between nucleus and cytoplasm of the cell?(1 vote)
- Because there is a nuclear membrane segregating the two parts. Nuclear membrane is also semi-permeable, so it can also chooses what to let in and what to let out (via nuclear pore).(0 votes)
- animals come from animals? I do not get it why did he say that!(0 votes)
Video transcript
- [Voiceover] Alright, so in
order to describe cell theory, I'm gonna go ahead and tell you the story of how cell theory developed. Now, over here on the
right side of the screen, you notice a timeline that goes from the 1600's to the late
1800's and a couple boxes here. And these boxes will fill in as the three major tenets of cell theory, and they will correspond to
the different periods of time in which these tenets were developed. Throughout this story, I'm
gonna refer to examples of bacteria, plants, and animals to illustrate some of the points. So, the story starts off in
the Netherlands in the 1600's with a scientist by the
name Anton van Leeuwenhoek. Around this time, the microscope was actually invented in the Netherlands. And van Leeuwenhoek
started using a microscope and he actually invented his
own version of the microscope and started looking at everything he could get his hand's
on under the microscope. And, so, one day this curiosity brought him to look at
the gunk on his teeth. That's right, he looked at his dental scrapings under the microscope. And when he did so, he noticed many small animal-like creatures
that were moving around and one of them may have
looked something like this. And because he thought
these kind of looked like little animals he named them "Animacules". And, now of course, we
know that what he was looking at now were actually bacteria, but at the time bacteria
hadn't been discovered. And for this discovery
of these animacules, Anton van Leeuwenhoek is
frequently referred to as the father of modern microbiology. Now, around the same time,
there was an English scientist by the name of Robert Hooke
and Hooke also looked at all sorts of things under the microscope. And this isn't probably
how it actually happened, but it's a fun story that I like to think to help remind myself of this. I like to think that Robert
Hooke was at a party one night and they decided to pop a
couple bottles of champagne, and perhaps one of the corks
hit Robert Hooke in the head. He then grabbed that cork,
put it in his pocket, and the next morning he woke up and said, "I wonder what this cork would," "look like under a microscope?" So, he sliced it thin and
looked at it under a microscope and what he saw was something
that looked like this. And what he was seeing was the remnants of the cells in the
plant that made the cork. And he thought that these
spaces kind of looked like the little dormitory rooms that monks lived in in a monastery. And these rooms in Latin
are known as "cellula" and so this is where the
term cells came from. And then, similarly, other scientists were looking at animal tissues, and they also noticed that
in different animal tissues, there were these similar cells, as in bacteria and plants, and from this, they developed the first
tenant of cell theory. And that is that the cell is the basic unit of structure in life. Now, over the ensuing
years, scientists continued to look at all sorts of
things under the microscope. And in regards to bacteria,
what they discovered was that there's all sorts of bacteria. One's like the one we saw above here, or can maybe kinda rod-shaped. Or there was bacteria
that were spiral-shaped and there's bacteria
that were more spherical. And what they discovered was that, regardless of the shape of these bacteria, they all had the same
cell as their structure, this basic unit of structure. So, moving on to plants,
in the 1830's there was a German botanist by the
name of Matthias Schleiden. And like I said, Schleiden was a botanist, and he also was interested
in microbiology, so he looked at all sorts of
plants underneath a microscope. And what he realized was,
it didn't matter whether he was looking at a
specific type of flower or if he was looking at a maple tree. All the different plants he looked at had the same microscopic structure that Robert Hooke had described a couple hundred years
earlier of these cells. Then, at the same time,
another German scientist by the name of Theodor
Schwann was looking at the nervous systems of different animals. And what he realized was it didn't matter if he was
looking at a human or a cat. No matter what type of animal, they all had a similar
structures that were these cells. And luckily for microbiology,
Schleiden and Schwann in 1837 were actually at
a dinner party together. And they began discussing
each other's work. And I gotta imagine a
light bulb just went off in both of their heads and
they really discovered, you know, if all plants are made of cells and all animals are made of cells, it must be that all living
organisms are made of cells. And the next year in
1838, Schwann published and in this book he stated this finding that all living things
are composed of cells. Now, this was all well and good, because at the time no one really argued that all living things were made of cells. However, scientists didn't really know where the cells actually came from. Through observations,
some of this was known. For instance, it was known
for thousands of years that if a female and a male mated, you know over some period of time afterwards they would have an offspring. And so it was generally accepted that animals came from animals, and similarly in plants, it was well known that a tree or a plant,
say this one right here, would produce a seed and
that seed could then be planted in the ground and
it would then produce a tree or a plant that looked similar to the one that produced the seed. So, it's pretty well accepted
that plants came from plants. However, in bacteria it wasn't really clear where they came from. And the predominant theory at the time was something known as "Abiogenesis". So let me just erase some of our work here in order to describe this
theory of "Abiogenesis". Now, "Abiogenesis" is
actually a very old theory. It dates as far back as the
4th century BC with Aristotle. And up to the 1800's, this was really the predominant theory of how
life came into existence. So let's just kind of describe
"Abiogenesis" here briefly. Imagine you have, let's say, a rock. This is a rock. And what scientists thought at the time was that there was some
unknown substance in the air and that it would combine with
these non-living materials, such as a rock or whatever it might be, and from that, it would produce life. The mechanism of this theory was thought to be that of
spontaneous generation. The idea that life was
spontaneously made from non-life. Now, in the late 1800's, the scientists who were studying cells
began to refute this theory. And, one such scientist was the German physician and
pathologist, Rudolph Virchow. Now, Virchow was using his
microscope to look at cells. And what he observed
was that some bacteria, if you watch them at
the right point of time, they actually divided
and formed two bacteria that were identical,
at least in appearance, to the first bacteria. Now today we call this
mechanism binary fission and it's the means by
which bacteria reproduce. But the time that wasn't known, and so Virchow observed
this and he published this in a very famous work a
phrase in which he stated, "Omnis cellula e cellula," which roughly, translated from Latin, means "Every cell originates
from a cell like it." So, it's this idea that cells are not made by spontaneous generation,
but cells produce cells. And it is important to note that although Virchow is generally given
credit for this theory, the phrase "omnis cellula e cellula" was actually coined earlier
by a French physician by the name of François-Vincent Raspail and this theory of binary
fission was actually likely plagiarized from Robert
Remak, a Polish physiologist. So, Virchow, although he didn't come up with the idea or the term, he still for some reason
is generally given credit. But Virchow, he received a lot
of criticism for this theory. And other scientists who
believed in this "Abiogenesis" they stated, "Oh, this idea
that cells produce cells," "That might be true, but it doesn't," "By any means, disprove Abiogenesis," "I mean, both of these mechanisms," "Could be going on in the world." And, so this is where the
very famous French scientist Louis Pasteur enters
our story in the 1860's. Now, during this time, Louis
Pasteur did a very famous experiment known as the
Swan-Neck Bottle experiment, which kind of finally laid to rest this theory of Abiogenesis. So, before I describe the
Swan-Neck Bottle experiment, let me describe an
experiment that some of the proponents of Abiogensis used
as evidence for their theory. So, imagine you have a flask and you fill this flash with some broth and the broth may have
some bacteria in it. Well, it was known that
if they boiled the broth, they heated up and boiled it,
that would kill the bacteria. You could sterilize the
broth in this flask. And then, over time, if
the flask was left alone, what would happen is that bacteria would start to grow in it
and you'd get this growth and proponents of "Abiogenesis" said, "See, nothing was added to the flask," "And, yet, bacteria was formed," "It must have been formed
through spontaneous generation," "As no living organisms were added to it." However, Pasteur disagreed with this and so he came up with his own flask, known as a swan-neck bottle. It looked something like this, and this swan-neck flask
was also filled with broth and sterilized by boiling it, and what Louis Pasteur theorized was that there was actually maybe some bacteria, or living particles in the air, that would fall into the broth here, and that is what caused the growth. So, by creating this swan-neck, he was still allowing the
broth to be exposed to air and this potential unknown
substance in the air, but if there were any microorganisms
in the air that fell in they would be collected
in this curve of the neck and they wouldn't reach the broth. And, lo and behold, over
time, there was no growth. Like I mentioned earlier,
this kind of once and for all put to rest this theory of "Abiogenesis" and really established the
third tenet of cell theory and that is that all cells
come from preexisting cells. So, this is the story of cell theory and how scientists over
a period of 200 years really discovered the three
major tenets of cell theory that are really the foundation
of much of modern biology. And these are that the
cell is the basic unit of structure in life and
that all living organisms are composed of cells and that all cells come from preexisting cells.