Microscopes

Question 1

what is the definition of cells?

Answer 1

• basic structural unit of all living things

Question 2

what are the three elements of cell theory?

Answer 2

• all living organisms are made up of one or more cells
• cells are the basic functional unit in living organisms
• arise from pre-existing, living cells

Question 3

how do electron microscopes work?

Answer 3

use a beam of electrons rather than light

Question 4

what is resolving power or resolution?

Answer 4

ability to see two points distinctly

Question 5

what are the two types of electron microscopes?

Answer 5

Transmission Electron Microscope and Scanning Electron Microscope

Question 6

what is the Transmission Electron Microscope?

Answer 6

• Electron beam passes through a thin prepared sample
• Used to view 2D cross sections of material

Question 7

what is the Scanning Electron Microscope?

Answer 7

• Electron beam directed onto a sample
• don’t pass through, bounce off
• produce a 3D image

Question 8

what are the differences of electron microscopes over light microscope?

Answer 8

• very expensive
• very hard to use
• no colour
• dead specimens only
• higher resolving power

Question 9

what are the benefits of light microscope over electron microscopes?

Answer 9

• relatively inexpensive
• easy to use
• coloured image
• can use living specimens
• lower resolution

Question 10

what stains used for light microscope?

Answer 10

• coloured dyes
• fluorescent stains
• immunofluorescence

Question 11

what stains used for electron microscope?

Answer 11

• heavy metal stains
• freeze staining

Question 12

issues with heavy metal staining?

Answer 12

often toxic

Question 13

what are stains used for?

Answer 13

used in light microscopy to make thin, colourless samples visible

Question 14

how do fluorescent stains work?

Answer 14

• chemicals which absorb one wavelength of light and re-emit it as another
• viewed under special fluorescence detecting light microscope

Question 14

how does immunofluorescence work?

Answer 14

• fluorescent stains attach to antibody
• antibody = very specific & only bind to certain target molecules
• ∴ can be used to detect oresence of target molecules (often proteins) on a slide
• fluorescence detecting light microscope detect presence of fluorescence stain attached to antibody

Question 15

what is freeze fracturing used for?

Answer 15

• way of preparing sections through cells for viewing through a SEM

Question 16

how does freeze fracturing work?

Answer 16

• sample of cells rapidly frozen 190°C
• sample then fractured, breaking
  frozen cells open
• vapour of platinum or carbon stain
  passed over surface of broken cells
• forms a coating - can be view under
  SEM

Question 17

what is cryogenic electron microscopy?

Answer 17

technique used to visualise strucure of individual proteins
- thin layer of pure protein solution
flash frozen to -182°C
- frozen sample then view with
high powered SEM + images
taken from diff angles
- computer enhancements of
images used to build up a 3D
image of that protein