Microbiology

Question 1

What is a bacterial cell wall made of?

Answer 1

Peptidoglycan/murein

Question 2

What size are bacterial ribosomes?

Answer 2

70s

Question 3

How would you describe bacterial DNA?

Answer 3

Circular, free in the cytoplasm, also in smaller plasmids

Question 4

How do bacteria move?

Answer 4

The flagellum

Question 5

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

Answer 5

Bacillus, coccus, spirillum

Question 6

How are eukaryotic cells different to prokaryotic cells?

Answer 6

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

Question 7

Describe the cell wall of a gram positive bacterium

Answer 7

A thick layer of peptidoglycan

Question 8

Describe the cell wall of a gram negative bacterium

Answer 8

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

Question 9

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

Answer 9

Gram positive purple, gram negative pink/red

Question 10

What are the four steps in a gram stain?

Answer 10

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

Question 11

What conditions are required for bacterial growth?

Answer 11

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

Question 12

Define obligate aerobe

Answer 12

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

Question 13

Define obligate anaerobe

Answer 13

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

Question 14

Define facultative anaerobe

Answer 14

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

Question 15

What is the purpose of aseptic technique?

Answer 15

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

Question 16

Give three examples of aseptic technique

Answer 16

Flame equipment until red hot to sterilise, use an autoclave to sterilise other equipment, 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 17

Give two reasons it is difficult to count bacteria

Answer 17

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

Question 18

What are total and viable counts?

Answer 18

A total count includes both living and dead bacteria, a viable count is only living bacteria

Question 19

Give the advantages of a total cell count using a haemocytometer

Answer 19

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

Question 20

Give the disadvantages of a total cell count using a haemocytometer

Answer 20

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

Question 21

Give the advantages of a viable count using serial dilution

Answer 21

You can count only the living bacteria

Question 22

Give the disadvantages of a viable count using serial dilution

Answer 22

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 23

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

Answer 23

Each colony only comes from one bacterium