microscopy Flashcards
what does an optical microscope use to view images
Light rays
Give the maximum resolution of an optical microscope
0.2 micrometres
State 3 organelles that CAN NOT be seen under an optical microscope
Ribosomes , ER and lysosomes
What is the useful magnification of an optical microscope
x1500
Give 3 advantages of optical microscopes
cheap, portable, easily used
Give 2 disadvantage of optical microscopes
limited resolution, cant distinguish between objects closer than half a wavelength
low magnification in comparison to electron microscopes
electron microscopes use electrons to form an image, why does this give electron microscopes a higher resolution that optical?
Electron rays have a much smaller wavelength than light rays so images can be distinguished more easily
What is the maximum resolution of an electron microscope
0.0002 micrometers / 0.2nm, 1000x greater than light microscopes
Why is having a greater maximum resolution an advantage to electron microscopes
Smaller organelles can be viewed
Give the maximum useful magnification of an electron microscope
x1,500,000
How do transmission EM’s view specimens
Using an electromagnet to focus a beam of electrons which is transmitted through a specimen
Why do denser areas of a specimen appear darker under a transmission EM?
Denser areas of the specimen absorb more electrons which makes it appear darker
Give an advantage of using a transmission EM
They provide high resolution images which allows internal structures within the cell to be seen
Give 2 disadvantages of using transmission EM’s
They can only be used to observe very thin specimen
Cannot be used to observe live specimens, only dead
How do scanning EM’s view a specimen
Uses focused beams of electrons which are bounced/reflected off the specimens surface, gathered in a cathode ray tube to form an image
