Cell Structure 2.1

Microscopes

Magnification- The number of times larger the image appears compared to its actual size

Resolution- The amount of detail that the image has, how distinguished the difference between two objects is.

Optical (light) microscopes
The optical microscope is the first microscope to aid the understanding of the cell structure. Though other microscopes have been developed the light microscope is still used in schools, hospitals, colleges and research labs as they are cheap, portable, easy to use and can be used to study whole specimens. The optical microscope has a magnification of up to x2000 however most remain at x1500. Optical microscopes use visible light at a wavelength of 400-700nm (0.4-0.7Mm) in length, therefore if any specimen under a light microscope has a gap between two objects shorter than 200nm (0.2Mm) it will appear as one image.

Laser Scanning Microscopes
Laser scanning microscope are also referred to as confocal microscopes. These microscopes use a laser light system which then shows the image on a computer. The images have a high resolution. These microscopes also have depth selectivity and therefore can show different depths into the specimen and can show a whole specimen.

Electron Microscopes
There are two types of electron microscope, the transmission electron microscope and the scanning electron microscope.

Transmission Electron Microscope- To use one of these the specimen has to be chemically drained and fixed with a staining. A beam of electrons passes through the specimen which is stained with metal salts. Some electrons pass through and are focused on the screen. The electrons form a 2D black and white image. When it is photographed it is an electron micrograph. TEM’s have a magnification up to x2,000,000 and they are being developed so they can reach up to x50,000,000.

Scanning Electron Microscope- Electrons cannot pass through the specimen as it is whole but they can bounce off and be focused on to a screen. The screen gives a black and white 3D image which can be turned into a colour image using a computer program. When holding the specimen down it must be held in a vacuum and coated with a fine film of metal. The scanning electron microscope has a x200,000 magnification.

Slides and Photomicrographs
Unstained Specimens
Many biological structures such as single celled organisms are colourless and therefore and difficult to see under a light microscope. Therefore the way to see them without using the staining method is to place them on a darkened background. Microscopes which can do this are the light microscopes as the light setting beneath can be adjusted and therefore live specimen can be seen with ease. 

Stained Specimens
Stains are coloured molecules that bind to the molecules in or on the specimen and thus make it easier to see. Some stains bind to any cells structure and some only bind to specific cell structure therefore the specific stain highlights the structure of that particular organism. This is called differential staining, there are many stains that are…