Microscopes Flashcards Preview

Biology A Level > Microscopes > Flashcards

Flashcards in Microscopes Deck (17):
1

Magnification

How much bigger object appears compared to original size

2

Resolution

Clarity, ability to distinguish between 2 points close together

3

How do optical microscopes work?

Lenses focus beam of light

4

Optical microscope advantage

Cheap
Easy use
Portable (can use in field)
Study whole living specimens
Up to x1500 magnification

5

Optical microscopes disadvantages

Limited resolution
Higher magnification gives unclear image
Can't tell apart structures closer together than 200nm
Can't see ribosomes (20nm)

6

How do Laser scanning microscopes work?

Use laser light to scan object, display on computer

7

Laser scanning microscope advantage

High resolution
High contrast
Depth selectivity (observe whole as well as cells)

8

2 electron microscope types

Scanning
Transmission

9

How do electron microscopes work?

Beam of electrons fired from cathode, focused by magnets onto screen

10

Electron microscope advantage

Greater resolution
Clear highly magnified

11

Electron microscope disadvantage

Large
Expensive
Skill/training needed
Specimens dead
Metallic salt stains hazardous

12

How do Scanning electron microscopes work?

Electrons cause secondary electrons to bounce off specimens surface. Focused on screen

13

Scanning electron advantage

3D image
Black and white but computer can add colour
Magnification: less than transmission but quite high (x15-x300 000)

14

Scanning electron disadvantages

Specimen in vacuum
Coated with fine film of metal

15

How do Transmission electron microscopes work?

Electrons pass through specimen
focused on screen
Forms electron micrograph

16

Transmission electron advantage

Magnification highest (x2million)

17

Transmission electron disadvantages

Specimen chemically fixed, dehydrated, stained with metal salts