1. Microscopes Flashcards
What is magnification?
Describes how much bigger an image appears compared with the original object.
What is resolution?
The ability of an optical instrument to see or produce and image that shows fine detail clearly.
What are the advantages of optical microscopes?
Relatively cheap
Easy to use
Portable and able to be used in the field as well as in laboratories
Able to study whole living organisms
What is the optimum magnification of optical microscopes?
x 1500 sometimes x 2000
What is the magnification equation?
total magnification = magnification of objective lens x magnification of eyepiece lens
What is a pictomicrograph?
the image seen using an optical microscope
How do laser scanning (confocal) microscopes work?
They use laser light to scan an object and assemble, by computer, the pixel information into one image on a computer screen.
What are the advantages of laser scanning microscopes?
The images are high resolution and show high contrast.
The images have depth selectivity so can focus on different depths of the whole specimen.
How do electron microscopes work?
They use a beam of electrons from a cathode with a wavelength of about 0.004nm
What are the advantages of electron microscopes?
They have a much greater resolution that optical microscopes.
They give very clear, highly magnified images
How do transmission electron microscopes work?
The specimen is chemically fixed by being dehydrated and stained with metal salts.
The beam of electrons passes through the specimen.
Some electrons pass through and are focused on the screen or photographic plate
What do transmission electron microscopes produce?
The electrons form a 2D black-and-white image. This is called an electron micrograph.
What are the advantages of transmission electron microscopes?
They can produce a magnification of up to 2 million times.
How do scanning electron microscopes work?
The specimen has to be placed in a vacuum and coated with a fine film of metal.
Secondary electrons ‘bounce off’ the specimen’s surface and are focused onto a screen.
What do scanning electron microscopes produce?
A 3D image with a magnification from x15 to x200,000.
The image produced is black and white but computer programmes can add false colour
What are the disadvantages of both electron microscopes?
They are large and very expensive.
They need a lot of training to use.
What is differential staining?
When certain stains bind to specific cell structures, staining each one differently so the structures can be can be easily identified.
What stains are used for differential staining?
Acetic orcein binds to DNA and stains chromosomes dark red.
Eosin stains cytoplasm.
Sudan red stains lipids.
Iodine in potassium iodide solution stains the cellulose in plant cell walls yellow and starch granules blue/black.
How are specimens prepared before observation?
Dehydration
Embedding them in wax to prevent distortion during slicing
Staining and mounting in chemicals for preservation
