SSER Ltd Light Microscope Electron Microscope

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Light Microscope Electron Microscope Advantages Disadvantages Preparing specimens relatively simple Expensive to buy Expensive to run when generating the electron beam Preparing specimens is a complex procedure Living and dead tissue may be observed Living specimens cannot be observed Relatively cheap to buy Cheap to run using little electricity Colour images are obtained Disadvantages Resolution limited by the wavelength of light Depth of field is restricted Limited magnification (approximately x 1500) Images are black and white Advantages High resolution Greater depth of field may be observed High magnifications up to 250, 000

Electron micrographs and photomicrographs show specimens that have been magnified to different extents In order to gain a sense of proportion and size from such images, it is necessary to be able to interpret magnification data and scale lines drawn on the image Magnification is a value that tells us how much larger an image is when compared to the original object Magnification = size of image size of object Both values must be converted to the same units before the magnification is calculated If an image measures 30 mm and the specimen or object measures 3 mm then the image value must first be converted to mm 30 mm = 30, 000 mm So, magnification = 30, 000 3 = 10, 000

The ACTUAL SIZE of an object can be calculated using the same formula: Magnification = size of image size of object THEREFORE: Size of object = size of image magnification If an image is measured and found to have a length of 6 mm (6, 000 mm) and the magnification is 40, 000 then: Actual size of object = 6, 000 40, 000 = 0. 15 mm

This electron micrograph of a longitudinal section of skeletal muscle shows the myofibrils and Z-lines of the sarcomeres (magnification x 75, 000) Z line We wish to know the actual length of the Sarcomere, i. e. the distance from one Z-line to the next A ruler is used to measure the length of a sarcomere in millimetres This distance is found to be 130 mm (130, 000 mm) USING THE FORMULA: Size of object = size of image magnification Actual length of sarcomere = 130, 000 75, 000 = 1. 73 mm Z line Courtesy of Dr. H. Huddart – Department of Biological Sciences, The University of Lancaster

The magnification can also be determined from scale lines drawn on images Magnification = length of scale line measured length of scale line given The scale line given on this image has a value of 5 mm When this line is measured with a ruler, it is found to have a length of 30 mm (30, 000 mm) THEREFORE: Magnification = 30, 000 5 = 6, 000

The magnification value of x 6, 000 can be used to determine the actual dimensions of structures represented in the micrograph When the diameter of the red cell is measured with a ruler it is found to be 42 mm (42, 000 mm) The actual diameter of the red blood cell is therefore: size of image magnification 42, 000 6, 000 = 7 mm