Microbiology

Question 1

What is a bacterial cell wall made of?

Answer 1

Peptidoglycan/murein

Question 2

Answer 2

Question 3

What size are bacterial ribosomes?

Answer 3

70s

Question 4

How would you describe bacterial DNA?

Answer 4

Circular, free in the cytoplasm, also in smaller plasmids

Question 5

How do bacteria move?

Answer 5

The flagellum

Question 6

What are the proper terms for rod shaped, spherical and spiral bacteria?

Answer 6

Bacillus, coccus, spirillum

Question 7

How are eukaryotic cells different to prokaryotic cells?

Answer 7

They contain membrane bound organelles, including the nucleus. They have linear rather than circular DNA and larger 80s ribosomes

Question 8

Describe the cell wall of a gram positive bacterium

Answer 8

A thick layer of peptidoglycan

Question 9

Describe the cell wall of a gram negative bacterium

Answer 9

A thin layer of peptidoglycan with an outer layer of lipoprotein and lipopolysaccharide

Question 10

What colour do gram positive and gram negative bacteria stain with a Gram Stain?

Answer 10

Gram positive purple, gram negative pink/red

Question 11

What does ethanol do to the gram negative bacteria in the gram stain?

Answer 11

It removes the lipopolysaccharide layer, washing away the crystal violet/iodine

Question 12

What are the four steps in a gram stain?

Answer 12

Add crystal violet, add iodine, add ethanol, add safranin

Question 13

What conditions are required for bacterial growth?

Answer 13

The correct oxygen levels, correct temperature, correct pH, a carbon source, a nitrogen source, minerals

Question 14

Define obligate aerobe

Answer 14

Bacteria that can only survive/divide in the presence of oxygen

Question 15

Define obligate anaerobe

Answer 15

Bacteria that can only survive/divide in the absence of oxygen

Question 16

Define facultative anaerobe

Answer 16

Divide faster in the presence of oxygen but can survive in its absence

Question 17

What nutrients do bacteria need?

Answer 17

A carbon source (eg glucose), a nitrogen source (eg amino acids) vitamins, mineral ions

Question 18

What is the purpose of aseptic technique?

Answer 18

To prevent contamination of the environment by the microbes being handled and contamination of microbial cultures by unwanted microbes from the environment

Question 19

How do you sterilise glassware?

Answer 19

Use an autoclave. The high temperature and pressure kills bacteria and spores

Question 20

How do you sterilise glass spreaders?

Answer 20

Dip in ethanol, pass through a flame and burn ethanol off to kill bacteria/spores

Question 21

How do you sterilise inoculating loops?

Answer 21

Hold in a roaring flame until red hot to kill bacteria/spores

Question 22

Why have a roaring flame on the desk?

Answer 22

To create an updraft, lifting air containing bacteria/spores up and away from the workspace

Question 23

Give five examples of aseptic technique

Answer 23

Flame equipment until red hot to sterilise, use an autoclave to sterilise glassware, keep roaring flame on desk to create updraft, open petri dish lid at angle to reduce contamination, do not put lids on desks to reduce contamination

Question 24

Give three reasons it is difficult to count bacteria

Answer 24

They are small, there are too many, it’s hard to tell if they are alive or dead

Question 25

What is a viable count?

Answer 25

A viable count is only counting living bacteria (eg those that have divided to form a colony on a plate)

Question 26

What is a total count?

Answer 26

A total count includes both living and dead bacteria (eg on a microscope slide)

Question 27

Give the advantages of a total cell count using a haemocytometer

Answer 27

It's fast and can be used for several types of cell at once

Question 28

Give the disadvantages of a total cell count using a haemocytometer

Answer 28

It includes dead bacteria, they may clump making it hard to count (still need to dilute), requires an oil immersion lens

Question 29

Give the advantages of a viable count using serial dilution

Answer 29

You can count only the living bacteria

Question 30

Give the disadvantages of a viable count using serial dilution

Answer 30

Could be an underestimate if each colony came from more than one bacterium (clumping occurs), takes time, some species may take longer to grow than others

Question 31

What is the assumption when doing a viable count from plates that have undergone serial dilution?

Answer 31

Each colony only comes from one bacterium

Question 32

Why wouldn't you count colonies on a plate with fewer than 30 colonies?

Answer 32

Too few to be statistically significant. This would decrease validity. Small sample size increases error.

Question 33

Why wouldn't you count colonies on a plate with a lot of colonies?

Answer 33

Too many colonies to count as they have merged/clumped. Each colony would not come from one bacterium.