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7981805
2.1.2 Slides and photomicrographs
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AS level Biology (2.1- Cell Structure) Mind Map on 2.1.2 Slides and photomicrographs, created by Aleena Sheraz on 06/03/2017.
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biology
2.1- cell structure
as level
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Aleena Sheraz
, updated more than 1 year ago
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Aleena Sheraz
over 7 years ago
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Resource summary
2.1.2 Slides and photomicrographs
Optical microscopes are used to view a wide range of specimens
Living organisms like paramecium and amoeba
Smear preparations of human blood and cheek cells
Thin sections of animal, plant or fungal tissue e.g. bone, muscle, leaf, root or fungal hyphae
Observing unstained specimens
Many biological structures are colourless and transparent
Some microscopes use light interference rather than light absorption = produces a clear image without staining
Some microscopes use a dark backdrop against the illuminated specimen
Useful for studying living specimens
Staining specimens
Stains= coloured chemicals that bind to molecules on/in the specimen making it easy to see
Methylene blue = all purpose stain
Differential staining= some stains bind to specific structures staining them each differently to be identified
Acetic orcein = binds to DNA, stains chromosomes dark red
Eosin = stains cytoplasm
Sudan red= stains lipids
Iodine (in potassium iodide solution)= stains cellulose in plant walls yellow and starch granules blue/black
Observing prepared specimens
Permanently fixed slide are made by experts in labs by:
Dehydrating specimens
Embedded in wax to prevent distortion when slicing
Special instrument makes v. thin slices (sections) which are stained and mounted in a special chemical to preserve them
Calculations involving magnification
If you know the magnification on a photomicrograph, you can work out the actual size of the strucutres
Measure the widest part in mm
Convert to um by X1000
Divide this by magnification (tells you actual size)
If you are told actual size of a structure on a photomicrograph and you measure the image size in um, you can calculate magnification factor
M: I/A
M= magnification factor
I= Image size, um
A= actual size
If magnification factor is 1000 it must be written as X1000
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