Transcript
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Introduces basic biology and the cell theory, then traces the development of microscopes from early lenses to the electron microscope. Explains how these tools changed scientists' understanding of cells and living organisms.
Speaker A
Hi, everybody.
So let's start to speak about basic biology.
During the early years of the 20th century, our understanding of genetic diseases and cancer was very limited.However, we understood that cells are the basic structure unit of every living organism.
The cell theory.The cell theory was developed during the mid-1600s.And like in any other major scientific progress, the cellular theory was a result of technological progress.The discovery of the microscope which took place at that time.
So the discovery of the microbes allow the scientists to see that all living organisms are made of cells and the new cells are created by all cells dividing into two.
So I would like to show you a short video which is going to tell you the story about the discovery of the first microscope and later on the discovery of the electronic microscope.
Speaker B
While the telescope has made it possible for us to view the cosmos, the microscope has allowed us to see the smallest components of all living things.
Magnifying glasses are mentioned in the writings of Roman philosophers during the 1st century AD.
But it wasn't until the 17th century that Galileo, the father of modern physics and astronomy, formulated the principle of lenses and focusing.
Robert Hooke built the first usable British compound microscope in 1665.It was a light microscope with two converging lens systems, the objective and the eyepiece.
Hooke observed that tissues were constructed of many tiny individual building blocks.In 1665, he had discovered and named the cell.
Hooke was actually viewing cork dead plant cells.
The first person to witness a live cell under a microscope was Anton van Leeuwen.
Around 1670, van Leeuwenhoek developed a method of grinding very thin glass lenses just a millimeter in diameter, and yet they could magnify by several hundred times.
These single lens microscopes were far superior to the early compound instruments.Mounted in a brass plate, these lenses could use transmitted light to image objects in a drop of water on the end of a metal pin.
A screw was used to move the pin and focus the specimen.
Van Leeuwenhoek was the first person to see and describe bacteria and yeast cells, sperm and blood cells, and witness the circulation of blood through capillaries.Light microscopes are still used today.But in 1931, German scientists Max Knoll and Ernst Ruske invented the electron microscope.Instead of light, this microscope employs a focused beam of electrons to image the specimen and is capable of far greater magnification and resolution.The electron microscope can magnify up to 1 million times, making it possible to view objects as small as the diameter of an atom.
These powerful microscopes have one major drawback.Living specimens are destroyed by the high radiation of the electron beam.So scientists must continue to rely on traditional light microscopes to examine living cells.
Compares light and electron microscopy for observing bacteria and other tiny structures. Also explains the size differences between cells and viruses, and why viruses are not considered cells.
Speaker A
So cells are the basic building units of life.This is the cell theory.
When you are looking on bacteria by light microscopy, usually you can see that it's there.You can use certain stains in order to get some more information about the bacteria, but you cannot really see the details so much.
But when you are looking on bacteria by using electron microscopy here, you can see quite a lot of details.Over here, you can see the cell wall of the bacteria, you can see a membrane, and you can see that the genetic material is replicating.And yes, you can see some other things as well.
So that's actually the big difference between electron microscopy and light microscopy.In electron microscopy, you cannot really see live bacteria, but when it comes to light microscopy, you can see the bacteria running around other cells, and you can actually use live organisms as well.
There are major differences when it comes to the cell size.Bacteria is a cell.Red blood cell is another cell.
So this human cell, the red blood cell, which considered to be as one of the smallest cells that we have around, is much, much, much larger as compared to the bacteria.
But if you take the bacteria, you're going to see that there are smaller things as compared to bacterial cells.Those are viruses.Viruses are not cells.They are not cellular life.They are parasites of cellular life.
They can enter the bacteria, they can enter a human cell, and then they can replicate indoor cells.In general, you can see that if we will go to the higher magnification, like here.Viruses have different shapes, and again, in terms of their size, they are much, much smaller as compared to the cells that they are going to infect.
Describes how viruses were finally visualized with electron microscopes and how that changed ideas about life. Then shifts to the distinction between unicellular and multicellular organisms and how cells coordinate in complex bodies.
Speaker C
Viruses have always been difficult to pin down.Even the most powerful optical microscopes could only magnify objects 2,000 times.
They revealed a watery world of bacteria and single celled creatures, eating, moving, multiplying.
What they couldn't see was the phantom that destroyed cells with stunning efficiency.
Then in the 1930s, German scientists invented the electron microscope and could finally see a virus at 7,000 times magnification.Instead of bouncing clumsy light waves off objects, it used tiny electrons to magnify.One look through the electron microscope instantly changed how people defined the boundaries of life.They discovered organisms so small, billions of and billions of them could fit into a single pixel on your television screen.
Scanned by electrons, viruses were revealed to be spheres and spindles and geometric shapes.They look too symmetrical to be alive.
Speaker A
The cell is the basic unit of all life forms.
Unicellular organisms for example, bacteria, yeast, etc.They are made up of just one cell.
Most of the organism on this planet are unicellulars, bacteria and other cells that you can find in the ocean.Most of them are unicellular organisms made up of one cell only.
Multicellular organisms are made up of several billions of cells.Like us, we are made out of approximately 50 times 10 in the power of 13 cells.So yes, like 50 trillion cells, more or less.And still those cells need to speak with each other.They need to coordinate their activity, and they need to be able to to send messages to each other.
The cells in multicellular organisms need to work together to help the organism to grow and survive.
Explains the difference between prokaryotic and eukaryotic cells, with examples from bacteria and human cells. Concludes with a simple overview of eukaryotic cell parts, including the membrane, cytoplasm, organelles, and nucleus.
Speaker A
We can identify two different cells.One of them that do not have a nucleus, and we call them prokaryotes.
And the other, usually larger cells that have a nucleus inside, and we call them eukaryotic cells.
We are eukaryotic organisms.Our cell container nucleus.
Bacterial cells are prokaryotic cells.They do not have a nucleus.The differences between those cells is far more significant than just the nucleus.
Human cells come in many shape and sizes.Some of them are quite long.
For example, neuronal cells, which have an extension from the main cell to speak with other cells.
Sperm cells that have a unique tail which allow the sperm to move.
Bone cells, smooth muscle cells, red blood cells.Each of them have its own unique shape, which is related to its function as well.
Red blood cells is the only cells that do not have a nucleus.
So we are going to speak today about eukaryotic cells.And in general, if we will start from the cell surface, we have a plasma membrane.
And when we go inside the set, we can see that cytoplasm that contain a lot of different things, like mitochondria.
We will talk about the mitochondria very soon.
And the endoplasmic reticulum, where proteins are being synthesized.And actually a lot of other things are being synthesized there as well, like lipids, Vesicles, we'll talk about them very soon.And the nucleus.
So in general, this is a simplistic way of looking at eukaryotic cell.