2.1.1. - Microscopy

Question 1

What are the 3 different types of Microscopes?

Answer 1

Electron microscope

Light microscope

Laser scanning confocal microscope

Question 2

What was the development of cell theory?

Answer 2

Schleiden —> Schwann —> Virchow

Question 3

What was Schleiden’s cell theory?

Answer 3

All plants are made of cells

Question 4

What was Schwann’s cell theory?

Answer 4

All animal tissues are composed of cells

Question 5

What was Virchow’s cell theory?

Answer 5

All cells must arise from pre-existing cells

Question 6

What does a Light microscope do?

Answer 6

Uses a simple light source to illuminate the specimen to project a magnified image

Question 7

What are the Advantages of a Light Microscope?

Answer 7

More accessible (cheap and small size)

No radiation

Can see living specimens (no vacuum needed)

Question 8

What are limitations of a Light Microscope?

Answer 8

Low resolution of only 0.2um

Low magnification of around x1500

Question 9

What is ‘Magnification’?

Answer 9

How large an image under microscope is compared to actual size

Question 10

What are the 4 ways of preparing specimens?

Answer 10

Dry mount

Wet mount

Squash Slides

Smear Slides

Question 11

What is ‘Resolution’?

Answer 11

Ability to distinguish between objects that are close together

Question 12

What is a Dry Mount?

Answer 12

Specimen is placed on the centre of the slide

Then a coverslip is placed over the sample

Question 13

What is a ‘Wet Mount’?

Answer 13

Specimen is suspended in liquid (water or immersion oil)

A coverslip is placed on from an angle.

Question 14

What types of specimen can be viewed in Dry Mount?

Answer 14

Pollen, hair, dust, insect parts can be viewed Whole this way

Question 15

What types of specimen can be viewed in Wet Mounts?

Answer 15

Aquatic samples and other living organisms

Question 16

What is a ‘Squash Slide’?

Answer 16

Wet mount is prepared

Then you squash the sample gently between 2 microscope slides.

Care needs to be taken so cover slip does not break

Question 17

What types of specimen are Squash Slides used for?

Answer 17

Soft samples

Root tip squashes are used to look at cell division

Question 18

What is a ‘Smear slide?’

Answer 18

Edge of a slide is used to smear a sample on another slide.

This makes a thin, even coating on another slide

Question 19

What types of specimen would you use Smear Slides for?

Answer 19

Blood as this is a good way to view cells in blood

Question 20

Why is staining used in light microscopy?

Answer 20

Staining is used to make parts of samples more visable

Question 21

What stain is used for Onion Tissue?

Answer 21

Iodine stain

Question 22

What stain is used for cheek cell?

Answer 22

Methylene blue

Question 23

What is ‘Gram stain technique’?

Answer 23

Gram positive bacteria will show up as blue/purple under a microscope.

Gram negative bacteria are Counter-stained and appear red/pink under a microscope

Question 24

What is ‘Acid-fast technique’?

Answer 24

Cells are dyed and washed with acid.

Mycobacterium are not affected and appear red

Other bacteria will become blue (exposure to methylene blue)

Question 25

What is Differential Staining?

Answer 25

When there is gram positive staining (purple) and gram negative staining (pink)

Question 26

What are the 2 different types of Electron Microscopes?

Answer 26

Transmission Electron Microscope (TEM) Scanning Electron Microscope (SEM)

Question 27

What are Electron Microscopes?

Answer 27

Exposes specimen to electrons. Electrons have a shorter wavelength than light Therefore has higher resolution and magnification

Question 28

What is a TEM?

Answer 28

TEM’s use electromagnets to focus a beam of electrons these are transmitted Through the specimen

Question 29

What are the advantages of TEM?

Answer 29

High resolution Shows internal structures

Question 30

What are the disadvantages of TEM’s

Answer 30

Cannot be used to observe live specimen Do not produces colour image Lengthy treatment to prepare specimens Can only be used on thin specimen

Question 31

What is a SEM?

Answer 31

SEM’s scan a beam of electrons Across the specimen. The beam bounces off the surface of specimen which are detected to produce image

Question 32

What are the advantages of SEM?

Answer 32

Can be used of thick or 3D specimens Allow external structure of specimens to be observed Produces 3D image (unlike TEM) Sections do not need to be prepared

Question 33

What are the Disadvantages of SEM’s?

Answer 33

Cannot be used to observe live specimen Does not produce colour image Gives lower resolution than TEM

Question 34

What is a Laser Scanning Confocal microscope?

Answer 34

Fluorescent dye is put on sample beforehand Beam of electrons/laser is reflected by fluorescent dyes. Multiple depths of tissue are scanned it is like building up an image from layer to layer

Question 35

What are the Advantages of Laser Scanning Confocal microscope?

Answer 35

Can be used on thick or 3D specimens Allow external structure to be viewed Very high resolution Colour images

Question 36

What are the Disadvantages of Laser Scanning Confocal microscopes?

Answer 36

Slow process and takes long time to obtain image Laser could cause Photodamage to the cells

Question 37

What are the 4 steps in preparing specimens for Electron Microscopy?

Answer 37

Fixation Staining Dehydration Embedding in Resin (TEM only)