Microscopes

Question 1

Define magnification

Answer 1

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

Question 2

Define resolution

Answer 2

degree to which it is possible to distinguish between two objects that are close together, higher resolution = greater detail

Question 3

What is the maximum magnification and resolving power of the light microscope?

Answer 3

x1500, 200nm (2 objects can only be distinguished if light waves can pass between them)

Question 4

What is the process and purpose of staining?

Answer 4

coloured stains are chemicals that bind to chemicals in/on the specimen, allowing it to be seen, some stains binds to specific cell structures

Question 5

2 examples of stains

Answer 5

Acetic orcein: stains DNA dark red, Gentian violet: stains bacterial cell walls

Question 6

What is the process and purpose of sectioning?

Answer 6

specimens embedded in wax, thin section cut without distorting specimen structure, useful for making sections of soft tissue e.g. brain

Question 7

What is a micrometer equal to in terms of meters?

Answer 7

1um = 0.000 001m (1 millionth of a meter)

Question 8

What is a nanometer equal to in terms of meters and micrometers?

Answer 8

1nm = 0.000 000 001m (1 thousand millionth of a meter, 1 thousandth of a micrometer)

Question 9

How long are animal cells usually in micrometers?

Answer 9

20um-40um

Question 10

How wide are cell surface membranes and what is the diameter of a ribosome in nanometers?

Answer 10

CSM = 10nm wide, ribosome = 20nm diameter

Question 11

What are the resolutions for the human eye, light and electron microscopes?

Answer 11

100um, 200nm, 0.1nm

Question 12

What is a graticule and what is it used for?

Answer 12

microscope eyepiece can be fitted with a graticule: transparent with small ruler on it, dimensions in eyepiece units (epu)

Question 13

What is a stage micrometer?

Answer 13

placed on microscope stage, used to calibrate epu, it is 1mm long with 100 divisions (every 0.01mm or 10um)

Question 14

What is the relationship between actual size, magnification and image size?

Answer 14

actual size= image size / magnification

Question 15

What are the 2 types of electron microscopes and what are their max magnifications?

Answer 15

transmission electron microscope: x500 000

scanning electron microscope: x100 000

Question 16

How does a transmission electron microscope work?

Answer 16

Beam directed onto very thin sample, electrons pass through denser part of sample less easily = contrast, 2D image

Question 17

How does a scanning electron microscope work?

Answer 17

Electron beam ‘bounced off’ sample, 3D image of surface

Question 18

What is the resolution of an electron microscope?

Answer 18

0.1nm

Question 19

3 disadvantages of using an electron microscope?

Answer 19

samples have be in vacuum: air mols deflect electrons, expensive, preparing samples needs training ans skill

Question 20

What are false-colour electron micrographs

Answer 20

Micrographs are always black, white and grey but images can be changed colour by a computer

Question 21

What are used as stains in electron micrographs?

Answer 21

Metal particles or metal salts