Microscopes Flashcards
Define magnification
degree to which the size of an image is larger than the object itself
Define resolution
degree to which it is possible to distinguish between two objects that are close together, higher resolution = greater detail
What is the maximum magnification and resolving power of the light microscope?
x1500, 200nm (2 objects can only be distinguished if light waves can pass between them)
What is the process and purpose of staining?
coloured stains are chemicals that bind to chemicals in/on the specimen, allowing it to be seen, some stains binds to specific cell structures
2 examples of stains
Acetic orcein: stains DNA dark red, Gentian violet: stains bacterial cell walls
What is the process and purpose of sectioning?
specimens embedded in wax, thin section cut without distorting specimen structure, useful for making sections of soft tissue e.g. brain
What is a micrometer equal to in terms of meters?
1um = 0.000 001m (1 millionth of a meter)
What is a nanometer equal to in terms of meters and micrometers?
1nm = 0.000 000 001m (1 thousand millionth of a meter, 1 thousandth of a micrometer)
How long are animal cells usually in micrometers?
20um-40um
How wide are cell surface membranes and what is the diameter of a ribosome in nanometers?
CSM = 10nm wide, ribosome = 20nm diameter
What are the resolutions for the human eye, light and electron microscopes?
100um, 200nm, 0.1nm
What is a graticule and what is it used for?
microscope eyepiece can be fitted with a graticule: transparent with small ruler on it, dimensions in eyepiece units (epu)
What is a stage micrometer?
placed on microscope stage, used to calibrate epu, it is 1mm long with 100 divisions (every 0.01mm or 10um)
What is the relationship between actual size, magnification and image size?
actual size= image size / magnification
What are the 2 types of electron microscopes and what are their max magnifications?
transmission electron microscope: x500 000
scanning electron microscope: x100 000
How does a transmission electron microscope work?
Beam directed onto very thin sample, electrons pass through denser part of sample less easily = contrast, 2D image
How does a scanning electron microscope work?
Electron beam ‘bounced off’ sample, 3D image of surface
What is the resolution of an electron microscope?
0.1nm
3 disadvantages of using an electron microscope?
samples have be in vacuum: air mols deflect electrons, expensive, preparing samples needs training ans skill
What are false-colour electron micrographs
Micrographs are always black, white and grey but images can be changed colour by a computer
What are used as stains in electron micrographs?
Metal particles or metal salts
