Ch. 3 Observing Microbes Through The Microscope

Question 1

mm (millimeter)

Answer 1

• 1 × 10^-3 m

* 1,000 of a meter

Question 2

mcm (micrometer)

Answer 2

1 x 10^-6 m

1 millionth of a meter

Question 3

nm (nanometer)

Answer 3

1 x 10^-9 m

1 billionth of a meter

Question 4

What is the average size of a bacterium?

Answer 4

3 mcm

Question 5

What is the highest magnification of a binocular Compound Light Microscope?

Answer 5

1000x

Question 6

What magnification do you go to when observing bacteria?

Answer 6

Highest (1000x)

Question 7

Bacteria are considered to be what type of cell?

Answer 7

Unicellular

Question 8

When light from a microscope scatters, what does it do to your image?

Answer 8

• Compromises the image quality

Question 9

What is refraction?

Answer 9

• Bending/scattering of light, includes air (higher the refractive index the more it bends)

Question 10

What is the purpose of using pure mineral oil?

Answer 10

Causes the refractive index to lower, therefore causing less light to scatter (has a lower refractive index than air)

Question 11

What’s resolution?

Answer 11

• Clarity and sharpness

Question 12

What’s contrast?

Answer 12

Range of light and dark values in an image (the greater the range of light/dark values the higher the contrast)

Question 13

Bright field

Answer 13

• The entire field of view is (lit up) illuminated uniformly
• Ex. paramecium
  
  • Pellicle somewhat distinguishable
  • Less distinguished between the inner and outer boarder
  • Can see cilia
  • Can’t observe nucleus

Question 14

Dark field

Answer 14

Uses a special condenser with an opaque disk that blocks light from entering the objective lens directly.

- No cilia observed
- Vacuoles & nucleus can be seen
- Illuminated pellicle but the boarders a fuzzy
- Stain introduces and increases contrast 
- Examine live microorganisms that are either invisible in the ordinary light microscope. Cannot be stained by standard methods

Question 15

What are the different types of light illumination from the compound light microscope?

Answer 15

• Bright field
• Dark field
• Phase contrast

Question 16

What are the two types of compound lens?

Answer 16

• Objective
  
  • Highest magnification 100x (oil immersion lens)
    - Light scatters bc it hits the small air space
    - 4 diff magnification
• Ocular
  - Fixed magnification @ 10x

Question 17

What is the resolution limit?

Answer 17

• 0.2 mcm

* Amount of distance btwn two objects before they look like they’re touching

Question 18

What are the two most common types of electron microscopy (EM)?

Answer 18

• Transmission

* Scanning

Question 19

What color does each stain for the Gram Stain?

Answer 19

• Gram positive = purple

* Gram negative = pink

Question 20

Name the two types of helminths?

Answer 20

• Worm & Flukes

Question 21

What can you focus the electron beams and change their direction with?

Answer 21

Electromagnets

Question 22

Where is fluorescence generated for the EM?

Answer 22

By the flow of electrons

Question 23

Give examples of photosynthetic microbes?

Answer 23

Algae & Cyanobacteria

Question 24

Phase Contrast

Answer 24

• Condenser containing an annular (ring-shaped) diaphragm
  
  • Can observe sharpness and graininess of the internal structures of the cytoplasm
  • More defined vacuoles
  • Better resolution in the cytoplasm than in the dark field
    Clear distinction of the inner and outer pellicle

Question 25

What does staining introduce?

Answer 25

Contrast

Question 26

Phase Contrast

Answer 26

• Condenser containing an annular (ring-shaped) diaphragm
  
  • Can observe sharpness and graininess of the internal structures of the cytoplasm
  • More defined vacuoles
  • Better resolution in the cytoplasm than in the dark field
    Clear distinction of the inner and outer pellicle

Question 27

What does staining introduce?

Answer 27

Contrast