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Biology Topic 2A+B > Microscopy > Flashcards

Flashcards in Microscopy Deck (14)
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1
Q

Magnification equation

A

M=I/A
M= scale line measured/scale line given

2
Q

What is resolution?

A

the smallest distance between 2 particles which allows them to be distinguished from one another

3
Q

Why is the light microscope magnification and resolution limited?

A

The wavelength of invisible light is too long and the thickness of the sample

4
Q

Why does the electron microscope have a greater resolution?

A

they have a shorter wavelength than visible light so you can distinguish between objects

5
Q

Features of an SEM

A

Scanning electron microscope
- electrons are beamed onto surface and electrons are scattered depending on the contours (sheet/wave)
-3D- lower resolution than TEM
- can’t see internal structures
- specimen can be thick as electrons aren’t passed through

6
Q

Features of TEM

A

Transmission electron microscope
- fine beam of electrons that transmit/ pass through specimen
- denser parts of specimen absorb more electron so appear darker
-2D
- can see the internal structures / organelles - high resolution
- thin specimen stained and placed in vaccuum

7
Q

How do you prepare a microscope slide?

A

1.) Pipette a small drop of water onto the centre of the slide
2.) Use tweezers to place a thin section of the specimen on top of the water drop - needs to be thin to allow water through to see it clearly
3.) Add a drop of stain to highlight the organelles
4.) Add a coverslip - stand the slip upright on the slide and tilt and lower it so it covers the specimen - air bubbles will obstruct your view

8
Q

What is magnification?

A

how many times larger the image is compared to the object

9
Q

How do you work out the size of an object views with microscope?

A

use a graticule
the graticule must be calibrated each time you change the magnification to work out what the distance is between each division represents at that magnification

10
Q

How do you get from mm to micrometers (μm)?

A

x 1000
1mm = 1000μm

11
Q

How do you get from mm to nanometers (nm)?

A

x 1000000
1mm = 1000000nm

12
Q

How can you calibrate?

A

line up stage micrometer and graticule whilst looking through eyepiece and count how many divisions on the graticule fit into 1 division on micrometer scale - each division on micrometer is 10μm so calculate what 1 division is

13
Q

What are the features of an optical microscope?

A
  • beam of light condensed to create the image
  • poor resolution as wavelength of visible light is too long
  • low magnification -if sample is too thick light cant be let through
  • colour images
  • view living specimens
14
Q

What are features of an electron microscope?

A
  • beam of electrons condensed to create image - electromagnets used to condense beams
  • greater resolution as has shorter wavelength than visible light
  • higher magnification
  • black and white images
  • view non living specimens