Microscopy

Question 1

What does a microscope do to an image so it can be seen?

Answer 1

Magnifies it

Question 2

What is Resolution?

Answer 2

The ability to distinguish/see an object as two separate points and in detail

Question 3

Resolving power of a light microscope is limited to what?

Answer 3

The wavelength of light

Question 4

A light microscope had a limited..?

Answer 4

Maximum magnification

Question 5

How to electron microscopes work?

Answer 5

Uses a beam of electrons

Question 6

What are the advantages of an electron microscope over a light microscope?

Answer 6

Greater magnification

Greater resolution

Question 7

What are the disadvantages of an electron microscope?

Answer 7

Images can’t be seen with the eye
Images only seen in black and white
Has to be on ground floor

Question 8

Describe how electron microscopes work (4)

Answer 8

Cathode (tungsten filament) makes electricity and gives off electrons
Beam of electrons condensed by anode and passes through specimen
Beam focussed by EM lenses
Image formed on photographic plate

Question 9

What environment does the electron beam have to be in? Why?

Answer 9

A vacuum so the electrons aren’t dispersed by air particles

Question 10

What must the specimen be like for an electron microscope? (4)

Answer 10

Thin (sliced into fine sections using diamond blade)
Stained (aids contrast)
Dehydrated (water could effect electron beam)
Dead

Question 11

What is a transmission electron microscope? What picture does it produce?

Answer 11

When electrons go through the specimen

Provides a 2D image

Question 12

What is a scanning electron microscope? What picture does it produce?

Answer 12

The electrons bounce off the specimen surface and gives a 3D images (specimen coated with gold)

Question 13

What’s the first step of preparing for microscopy?

Answer 13

Chop up tissue using:
Ice Cold (stop enzyme reactions)
Isotonic (same conc./no water movement)
Buffered Solution (fixed pH)

Question 14

What’s the second step of preparing for microscopy?

Answer 14

Homogenisation - blended to produce uniform solution

Question 15

What’s the third step of preparing for microscopy?

Answer 15

Centrifugation - filter solution and use tubes that are spun at various speeds and separate organelles

Question 16

How to calculate/set up size measurement?

Answer 16

Use eyepiece graticule
Use a stage micrometer of known length
Record no. of eyepiece graticule units in one unit of the micrometer
Convert mm into micrometers 
Divide micrometer by eye piece units