Microscopes Flashcards
Magnification
How much bigger object appears compared to original size
Resolution
Clarity, ability to distinguish between 2 points close together
How do optical microscopes work?
Lenses focus beam of light
Optical microscope advantage
Cheap Easy use Portable (can use in field) Study whole living specimens Up to x1500 magnification
Optical microscopes disadvantages
Limited resolution
Higher magnification gives unclear image
Can’t tell apart structures closer together than 200nm
Can’t see ribosomes (20nm)
How do Laser scanning microscopes work?
Use laser light to scan object, display on computer
Laser scanning microscope advantage
High resolution
High contrast
Depth selectivity (observe whole as well as cells)
2 electron microscope types
Scanning
Transmission
How do electron microscopes work?
Beam of electrons fired from cathode, focused by magnets onto screen
Electron microscope advantage
Greater resolution
Clear highly magnified
Electron microscope disadvantage
Large Expensive Skill/training needed Specimens dead Metallic salt stains hazardous
How do Scanning electron microscopes work?
Electrons cause secondary electrons to bounce off specimens surface. Focused on screen
Scanning electron advantage
3D image
Black and white but computer can add colour
Magnification: less than transmission but quite high (x15-x300 000)
Scanning electron disadvantages
Specimen in vacuum
Coated with fine film of metal
How do Transmission electron microscopes work?
Electrons pass through specimen
focused on screen
Forms electron micrograph
