Unit 2- Microscopy

Question 1

What is resolution?

Answer 1

The smallest separation at which two separate objects can be distinguished

Question 2

What are the 3 kinds of microscopes?

Answer 2

TEM
SEM
Light microscope

Question 3

What causes the resolution limit of light microscopes?

Answer 3

The wavelength of visible light

Question 4

Why do samples need to be chemically stained in optical microscopes?

Answer 4

To make them stand out, as they are think cross sections

Question 5

Name 2 common stains used

Answer 5

Iodine to stain starch

Methylene blue to stain DNA

Question 6

Advantages of light microscopes:

Answer 6

Good magnification (x1000)
Can use living specimens
Coloured images

Question 7

Advantages of SEM

Answer 7

Gives 3D images

Don’t need thin sections

Question 8

Advantages of TEM

Answer 8

High magnification (x5000000)
Very good resolution

Question 9

Limitations of optical microscope

Answer 9

Poor resolution
Can’t see organelles
Specimens must be stained

Question 10

Limitations of TEM

Answer 10

Vacuum, so specimen cant be living
Specimen needs to be embedded in plastic
No colour (can be artificially inserted)
Specimens can be damaged by electron beam

Question 11

Limitations of SEM

Answer 11

Resolution not as good as TEM

Can’t see internal structures

Question 12

Uses of light microscopes

Answer 12

Tissue, cells and organisms

Question 13

Uses of SEM

Answer 13

Surfaces of living and non-living specimens

Question 14

Uses of TEM

Answer 14

Cell organelles, virus’ and bacteria

Question 15

How to remember difference between SEM and TEM

Answer 15

TEM-trickier

SEM-simpler

Question 16

How does a TEM work?

Answer 16

Thin cross section of non-living specimen embedded in plastic and stained has an electron beam shot through it in a vacuum

Question 17

How does a SEM work?

Answer 17

A fine beam of electrons is scanned onto a specimen, a computer detects all the electrons that have bounced off the surface and generates a computer image (super detailed but low magnification)

Question 18

Equation for magnification?

Answer 18

Magnification = image length/real length

Question 19

How to calibrate a microscopes

Answer 19

• calibrate the eye piece graticule
• place a stage micrometer slide on the microscope stage
• align the scales of the eye piece graticule and micrometer in the field of view under a weak magnification
• work out Length of each eyepiece unit