Topic 1 - Microscopes and Staining

Question 1

State the 8 parts of a light microscope

Answer 1

Eyepiece Lens + Objective lens
Ocular Tube
Stage
Iris Diaphragm
Light Source
Fine focusing wheel (small one)
Coarse focusing wheel (large one)

Question 2

State 2 types of light microscopes

Answer 2

Light (optical) Microscope
Laser scanning (confocal) Microscope

Question 3

State 2 types of electron microscopes

Answer 3

Transmission Electron Microscope

Scanning Electron Microscope

Question 4

What is a light (optical) microscope used to observe?

Answer 4

whole cells and tissues

Question 5

What is a transmission electron microscope used to observe?

Answer 5

organelles (as electrons pass through the specimen)

Question 6

What is a scanning electron microscope used to observe?

Answer 6

cell surfaces (as electrons bounce of the specimen)

Question 7

What is a laser scanning (confocal) microscope used to observe?

Answer 7

An object at a certain depth within a cell

Question 8

Which microscopes can be used to study living organisms?

Answer 8

Light (optical) microscope and laser scanning (confocal) microscope

Question 9

Give two key points about light (optical) microscopes

Answer 9

1: Uses light (wavelength of 400-700 nm) which is focused by glass
2: image produced is called a photomicrograph

Question 10

Give three advantages of light (optical) microscopes

Answer 10

1: Linear magnification of specimen
2: max magnification of x1500 to x2000
3: Stains don’t have to be used
(cheap, study living organisms, portable)

Question 11

Give two disadvantages of light (optical) microscopes

Answer 11

1: Limited resolution (200nm)
2: Doesn’t show cell ultrastructure

Question 12

Give two key points about laser scanning (confocal) microscopes

Answer 12

1: Laser light used and information is used to form an image on a computer screen
2: Emitted light is monochromatic (one wavelength)

Question 13

Give three advantages of laser scanning (confocal) microscopes

Answer 13

1: High resolution + linear magnification
2: Microscope had depth selectivity
3: Can be used to study living organisms

Question 14

Give two disadvantages of laser scanning (confocal) microscopes

Answer 14

1: Although magnification and resolution is high, it is still limited
2: Not easy to use - requires computer specialist

Question 15

Give three key points about transmission electron microscopes

Answer 15

1: Uses beam of electrons (wavelength of 0.004 nm) from a cathode
2: Electrons pass through specimen and these are focused onto a screen by magnets/photographic plate
3: 2D black and white electron micrograph produced

Question 16

What must be done to a specimen before it can be viewed using an electron microscope?

Answer 16

1: Specimens are fixed to preserve them
2: They are dehydrated (as electrons can heat the water)
3: embedded in wax and thin sections are prepared
4: they are examined in a vacuum

Question 17

Give three advantages of a transmission electron microscope

Answer 17

1: Very high magnification ( x2000000)
2: 0.1nm resolution
3: Internal structure of thin specimen can be seen

Question 18

Give three disadvantages of a transmission electron microscope

Answer 18

1: Large and expensive
2: Requires skill and training to use
3: Specimen must be dehydrated and examined in a vacuum
(cannot study living organisms)

Question 19

Give three key points about a scanning electron microscope

Answer 19

1: Uses beam of electrons (wavelength of 0.004nm)
2: Electrons bounce of specimen
3: 3D electron micrograph is produced - colour may be added by a computer

Question 20

Give three advantages of a scanning electron microscope

Answer 20

1: High magnification (x15 to x200000)
2: 0.1nm
3: whole specimen can be used and colour can be added

Question 21

Give three disadvantages of a scanning electron microscope

Answer 21

1: Large and expensive
2: Specimen had to be coated in a metal film
3: Specimen had to be viewed in a vacuum

Question 22

What is an eyepiece graticule?

Answer 22

A measuring device that acts as a ruler, superimposed on the specimen. It has 100 divisions.

Question 23

What is a stage graticule?

Answer 23

Measuring device on the stage which is used for calibration.

Question 24

Give the equation for the eyepiece division length

Answer 24

Eyepiece division length = Length of stage graticule/ Number of eyepiece divisions

Question 25

What do stains do?

Answer 25

Bind to molecules to help us view internal structures more clearly

Question 26

What is differential staining used to identify?

Answer 26

Different cellular components and cell types (they bind to structures differently)

Question 27

What are stains?

Answer 27

Coloured compounds/chemicals which bind to molecules, making the specimen easier to see.

Question 28

What does acetin orcein stain?

Answer 28

Stains chromosomes (dark red) - binds to DNA

Question 29

What does eosin stain?

Answer 29

Cytoplasm

Question 30

What does sudan red stain?

Answer 30

Lipids

Question 31

Give the calculation for magnification

Answer 31

magnification = image size/ actual size

Question 32

What is the difference between magnification and resolution?

Answer 32

Magnification is the number of times larger an image appears, compared to the size of the object. Resolution is fine detail.

Question 33

What is the magnification of a light microscope?

Answer 33

x1500 to x2000

Question 34

What is the magnification of a transmission electron microscope?

Answer 34

x2 000 000

Question 35

What is the magnification of a scanning electron microscope?

Answer 35

x15 to x200 000

Question 36

What is the resolution of a light microscope?

Answer 36

limited to 200nm

Question 37

What is the resolution of a transmission electron microscope?

Answer 37

0.1 nm

Question 38

What is the resolution of a scanning electron microscope?

Answer 38

0.1 nm