Observing cells

Discovering cells

In the early 1600s in the Netherlands there was a spectacle maker - Zacharias Jansen

He discovered the first compound microscope

The microscope soon became a hot item that every scientist wanted to work (play) with.
Anton van Leeuwenhoek instead of buying one of them made his own.
It was successful! So he started to discover the world around him including the gunk on his teeth :)

He discovered bacteria and called these organisms ‘animalcules’

​In 1665, Robert Hooke, an English architect and natural philosopher, designed and made working optical microscope.
He examined sections of cork, illustrated the smallest complete parts of an organism, which he called cells, because they were made up of regular compartments.

​To examine - to consider or study an idea, a subject, etc. very carefully

He called these small compartments cells, as they reminded him of the monks’ cells in a monastery.

In 1839 Matthias Schleiden and Theodor Schwann introduced their cell theory:

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In 1839 Matthias Schleiden and Theodor Schwann introduced their cell theory:

- All organisms are composed of one or more cells
- The cell is the smallest and basic unit of living organisms
- All cells come from preexisting cells

​The idea is: cells and their structures are extremely small, to study them we need to magnify them

Magnification - is a measure of how much bigger the image is than the actual object

​A compound light microscope; ​Specimen = object

The total magnification of the specimen is calculated as follows:

magnification of objective lens × magnification of eyepiece lens = total magnification

​objective magnification	​eyepiece magnification	​total magnification
​low - 4x	​10x	​
​middle - 10x	10x​	​
​high - 40x	10x​	​
​oil immersion - 100x	10x​	​

​Magnification - is a measure of how much bigger the image is than the actual object

​We can find a magnification using a formula (magnification triangle)

​Specimen = object

​Resolution determine how clear the image is.

Resolution - is a measure of how far apart two objects must be before we see them separately = the ability to distinguish between 2 objects

The limit of resolution of light microscope is about 0.2 micrometers. This means that 2 object less than 0.2 μm apart will always be seen as 1 object

Calculate the limit of resolution in nanometers

​The resolving power of an electron microscope is much higher than than of a light microscope

​What is the difference between magnification and resolution?

​Under the light microscope we can look at living organisms, tissues and cells.
But sometimes it can be difficult to identify some structures in 3D objects, so most of the specimens will be stained, specially sectioned (very thinly sliced) before they are mounted on a slide to get a better image

​to stain - to colour (a material or object) by applying a dye or chemical.

So what is the purpose of using stains?

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Light microscope VS Electron microscope

​Wavelength - 400 nm

​Wavelength - 1 nm

​The electron microscope can resolve detail down to less than 1 nm or 0.0001 μm, about 1000 times better than the light microscope

For the electron microscope to work, the specimens must be in a vacuum, so they are always dead. The preparation of a specimen for the electron microscope is a very complex process

​vacuum is space without matter and air

​2 main types of electron micrograph:

​TEM (transmission electron micrograph) - analysis 2D internal structures

​SEM (scanning electron micrograph) - analysis 3D surface of the sample

​Electron beam

​Let's compare light and electron microscopes on these points:

1. Cost/size/usage

2. Magnification

3. Resolution

4. Illumination source

5. Vacuum space

6. Colour

​Different units of length:

​Converting between m, cm, mm, μm, nm:

1. Convert 0,036 cm to mm

2. Convert 0,0578 cm to µm

3. Convert 0,0005584 mm to nm

4. Convert 191.000 µm to mm

5. Convert 63.700.000.000 nm to cm

6. Convert 2300 nm to µm

​Converting between m, cm, mm, μm, nm:

1. Convert 0.036 cm to mm = 0.36 mm

2. Convert 0.0578 cm to µm = 578 µm

3. Convert 0.0005584 mm to nm = 558.4 nm

4. Convert 191.000 µm to mm = 191 mm

5. Convert 63.700.000.000 nm to cm = 6370 cm

6. Convert 2300 nm to µm = 2.3 µm