BTEC Applied Science Unit 1 Biology Microscopes. What do we need to know about microscopes? Well, there are light microscopes and electron microscopes.
This is a light microscope. The specimen, the thing that you want to look on, is put on a slide, a piece of glass. You put a cover slip on top of it to make it nice and flat.
The specimen should be thin. so that light can pass through it and you shine light through it usually from below and then you look at it with the microscope. Sometimes you use a stain which helps you to see the different bits and pieces of what's going on. The bits of the microscope you need to know you've got your eye piece which is what you look in you've got your objective usually you've got several objectives so that you can change the magnification. The slide goes on the stage and you move the stage up and down.
There's a focusing knob and that will move the stage up and down until it's in focus and then some kind of a light source, a light bulb underneath which shines through the specimen. These are just some typical images of things, photographs taken through a light microscope. Can you identify any of them? Do you know what they are?
An electron microscope. Basically, if you're asked how does an electron microscope work, a beam of electrons is fired at the specimen, the electrons pass through the specimen, then they are detected and a computer produces an image from the way that the electrons have been scattered by the specimen. Okay, and these are some electron micrographs, pictures taken with electron microscopes.
The obvious difference is that you've got a much higher magnification, or you could say a much better resolution. Okay, much higher magnifications. Can you identify any of these? This is important.
A lot of students find this tricky. Magnification. Using this equation, I am. I is the size of the image.
A is the actual size. M is the magnification. So the magnification is the size of the image divided by the actual size.
So it's how much bigger it is, basically, is the magnification. For example, if the actual size is 0.1mm. and the size of the image is 20 millimeters then your magnification would be it would be 200 wouldn't it now the size of the image is found by looking at the scale on the eyepiece there's a thing on the eyepiece called a graticule and it has a scale on it usually it needs to be calibrated you'll be told something like these numbers are millimeters So that's done for you and here's your scale in millimetres and this is what we see through the microscope.
Then if we know that the magnification is 400, how big are these cells? Well, looking at this, it would be 2 millimetres divided by 400, wouldn't it? You must be comfortable with these.
1 mm, 1 mm, 1 times 10 to the minus 3, 0.001 meters is a millimeter, a thousandth of a meter. A micrometer, 1 mu m, that's the Greek letter mu, micro, 1 times 10 to the minus 6. Can you put that on your calculator? 0.0001 meters. A millionth of a metre is a micrometre.
You could get calculations involving either of these. Electron microscopes, advantages and disadvantages. Well, the advantage is much greater magnification, if you need it, compared to light microscopes.
You can see inside cells, you can see the organelles inside cells. The disadvantages, well they are much more expensive, they're very expensive. You need special training to use it and you can only examine dead material. Because you're blasting it with very fast moving electrons, you can only look at dead things.