2 Intro to the Bacteria, Microscopy & Staining

Question 1

Diff b/w eukaryotes and prokaryotes?

Answer 1

Eukaryote: Cells contain membrane-bound organelles

Prokaryote: Cells lack internal membrane-bound nucleus and other organelles

Question 2

Name 5 microorganisms, and indicate whether they’re prokaryotic, eukaryotic, or neither.

Answer 2

1. Bacteria (prokaryotic)
2. Fungi (eukaryotic)
3. Algae (eukaryotic)
4. Parasites (eukaryotic)
5. Viruses (neither)

Question 3

Name the 3 Domains/Kingdoms of life.

Answer 3

1. Eukarya (eukaryotic)
2. Bacteria (prokaryotic)
3. Archaea (prokaryotic)

Question 4

Name two characteristics of archaea.

Answer 4

1. Inhabit extreme envirs

2. Don’t cause human diseases

Question 5

Earliest lifeforms on the Earth?

Answer 5

Bacteria

Question 6

How are bacteria named?

Answer 6

They have binomial nomenclature:

1. Genus
2. Species

Question 7

How do we name bacteria that have identical genus and species but are slightly different from each other?

Answer 7

By adding a “strain” name to their binomial name.

Question 8

T or F: Bacteria are usually only referred to by their genus, species, and strain. Rarely do we consider their other taxonomic categories (e.g. their phylum, class, order, etc.)

Answer 8

T

Question 9

What’s the value of bacterial taxonomy? (3)

Answer 9

1. Consistency of communication
2. Assess relatedness of diff bacteria
3. For medical practice

Question 10

T or F: All strains of E. Coli cause the same disease

Answer 10

F

Diff strains of a bacteria can cause completely diff diseases.

Question 11

Up to what magnification can light microscopy reach?

Answer 11

1000x magnification

Question 12

T or F: Light microscopy is sufficient for most routine bacterial observations.

Answer 12

T

Question 13

Up to what magnification can electron microscopy reach?

Answer 13

200,000x

Question 14

Main drawback of electron microscopes?

Answer 14

Expensive, thus limited use

Question 15

2 advantages and 1 disadvantage of staining for light microscopy?

Answer 15

Advantage: Increase contrast of specimen
Advantage: Preserve specimen for future observation
Disadvantage: Staining kills microbe

Question 16

What method can be used so that the microbe ISN’T killed in the process of preparing it for observation via light microscopy?

Answer 16

Hanging Drop method (aka “wet mount”)

Question 17

Disadvantage of wet mount?

Answer 17

Poor contrast

Question 18

Advantage of wet mount?

Answer 18

Observe microbe movement.

Question 19

Term for a coloured dye that binds to bacterial cells?

Answer 19

Stain

Question 20

What’re the three steps involved in staining bacteria?

Answer 20

1. Smear layer of bacteria on glass slide
2. Fix the smear by air drying + mild heating
3. Flood fixed smear w/ dye and wash unbound dye away

Question 21

What step of staining kills the bacteria?

Answer 21

Air drying + heating the smeared slide

Question 22

What’re the 3 types of stains?

Answer 22

1. Simple stain
2. Differential stain
3. Special stain

Question 23

Describe the simple stain.

Answer 23

a. A single dye is used
b. All bacteria appear as same colour
c. Cannot tell if diff species are present

Question 24

Name two types of differential stains.

Answer 24

1. the Gram Stain

2. the Acid-Fast Stain

Question 25

Describe the steps of the Gram Stain (only the steps after heat-fixing the bacteria) (4)

Answer 25

1. Flood heat-fixed smear w/ purple stain (all cells = purple) 2. Add iodine (iodine allows stain to bind better; all cells are still purple) 3. Decolourize cells w/ alcohol (Gram neg. cells become colourless) 4. Counterstain w/ red dye (Gram neg. cells become red)

Question 26

What colour is a Gram positive cell?

Answer 26

Purple

Question 27

What colour is a Gram negative cell?

Answer 27

Red

Question 28

T or F: Most bacterial species are "acid-fast"

Answer 28

F Most are, in fact, NOT acid-fast

Question 29

What's the main difference b/w the acid-fast stain and the Gram stain?

Answer 29

The de-colourizing step - acid-fast stains use a harsher de-colourizing step (it uses acid-alcohol instead of alcohol)

Question 30

Give an example of a bacteria that is acid-fast.

Answer 30

Mycobacterium tuberculosis

Question 31

T or F: The dye of acid-fast bacteria are decolourized during the decolourizing step of acid-fast stains

Answer 31

F Acid-fast bacteria are cannot be decolourized, and so remain the same colour (red) throughout the procedure

Question 32

What are special stains used for?

Answer 32

To see structures that're not normally seen using light microscopy

Question 33

Give two structures that can observed using special stains.

Answer 33

1. Spores | 2. Flagella

Question 34

What is a "pure culture"?

Answer 34

A pop of bacteria consisting of only ONE species or strain. | All bacteria are genetically identical to one another.

Question 35

What method is used to get a pure culture of bacteria?

Answer 35

the "streak plate" method

Question 36

How can diff bacterial species be distinguished on an agar surface?

Answer 36

By "colony morphology"