microscopy

Question 1

why can’t light microscopes show certain structures?

Answer 1

resolution not good enough - wavelength too long

Question 2

how does a light microscope work?

Answer 2

light passes through the specimen and is focused by glass lenses

Question 3

what is magnification?

Answer 3

the degree to which the size of an image is larger than the object itself

Question 4

advantages of light microscopes

Answer 4

1. can view a wide range of specimens 2. specimens can be living

Question 5

disadvantages of light microscopes

Answer 5

1. magnification is only x1500 2. resolution is only 200nm 3. can’t see ultrastructure of cell

Question 6

disadvantages of transmission electron microscopes

Answer 6

1. specimen must be extremely thin 2. complex staining process required 3. specimen can’t be living - must be in a vacuum 4. image may contain artefacts
2. image is not coloured

Question 7

what is the equation for calculating one eyepiece graticule division

Answer 7

number of stage micrometer divisions x size of division / number of eyepiece graticule divisions

Question 8

what is resolution?

Answer 8

the shortest distance between 2 points on a specimen that can still be distinguished clearly

Question 9

advantages of scanning electron microscopes

Answer 9

1. magnification is x100,000 2. resolution is 20nm can see ultrastructure of cell 4. image is in 3D

Question 10

how do scanning electron microscopes work?

Answer 10

electrons bounce off sample and are detected by sensors

Question 11

how do transmission electron microscopes work?

Answer 11

electron beam passes through very thin sample

Question 12

disadvantages of scanning electron microscopes

Answer 12

1. specimen must be extremely thin 2. complex staining process required 3. specimen can’t be living - must be in vacuum 4. image may contain artefacts

Question 13

advantages of transmission electron microscopes

Answer 13

1. magnification is x500,000
2. resolution is 0.1nm - high resolution as wavelength of electrons is shorter
3. can see ultrastructure of cell

Question 14

what is the equation for magnification?

Answer 14

magnification = image size / actual size