✅3.4 -microbiology

Question 1

Give 3 ways that you could distinguish between types of bacteria in a school lab

Answer 1

Shape
Size
Staining characteristics

Question 2

Name 3 ways microbiologists could classify bacteria

Answer 2

Metabolic features
Antigenic features
Genetic features

Question 3

What are metabolic features?

Answer 3

The chemical reactions that occur in bacteria

Question 4

What are antigenic features

Answer 4

The proteins on/sticking out of the surface marker of the protein

Question 5

What are genetic features of bacteria

Answer 5

Difference in DNA and base sequences in DNA

Question 6

What 2 names can be given to the chemical whose 3D mesh gives the bacterial cell wall it’s structure

Answer 6

Peptidoglycan and Murein

Question 7

Does Gram positive and gram negative have a peptidoglycan layer?

Answer 7

Gram positive: thick layer of peptidoglycan

Gram negative: thin layer of peptidoglycan (not exposed)

Question 8

Does Gram positive and gram negative have lipopolysaccharide?

Answer 8

Gram positive: no

Gram negative: yes, covers the peptidoglycan layer

Question 9

Name steps 1&2 of gram staining for both + and -

Answer 9

1) crystal violet, all cells take up dye on outer layer

2) treat cells with iodine, all cells stay purple

Question 10

Describe step 3 of gram staining for both + and - bacteria

Answer 10

3) decolorisation with alcohol
Gram positive: the alcohol does not affect the stain so it remains purple
Gram negative: the alcohol dissolves the lipopolypolysaccharide layer which is stained,
As the layer dissolved the dye is removed (colourless)

Question 11

Describe step 4 of gram staining for both + and - bacteria

Answer 11

4) counter stain with safranin
Gram positive: the dye does not affect the purple stain as already stained purple
Gram negative: the peptidoglycan layer, now exposed is dyed red by safranin

Question 12

Why is gram negative bacteria harder to treat with antibiotics

Answer 12

Additional level on gram (lipopolysaccharide level) makes it harder to kill as extra protection.

Question 13

What 5 conditions are needed to culture bacteria in a lab

Answer 13

1. Water presence
2. Suitable temperature
3. Suitable nutrients (glucose and nitrogen)
4. Suitable pH
5. Suitable oxygen levels

Question 14

List 3 types of nutrients that are necessary for bacterial growth

Answer 14

1) glucose
2) nitrogen (building amino acids)
3) vitamins and mineral salts

Question 15

Define Obligate aerobe

Answer 15

Microorganisms that must have oxygen to carry out their chemical reactions. These organisms will die in the absence of oxygen.

Question 16

Define obligate anaerobe

Answer 16

Microorganisms do not need oxygen to carry out their chemical reactions. These organisms will die in the presence of oxygen

Question 17

Define facultative anaerobe

Answer 17

Microorganisms that respire aerobically but can respire anaerobically in the presence of oxygen

Question 18

Define aseptic

Answer 18

Conditions that aim to exclude the presence of unwanted microorganisms

Question 19

Give 2 reasons why we use aseptic technique during the microbiology experiments

Answer 19

To prevent contamination by the microbes being handled

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

Question 20

Name the 2 ways equipment can be steralised prior to microbiology experiments

Answer 20

Heat

Irradiation= heat labile (stable) plastics as many melt

Question 21

Describe aseptic steps that you could take to ensure there’s no bacteria there to start

Answer 21

• sterile Petri dish with irradiated heat liable
• sterile equipment in an autoclave 121 degrees for 15 minutes
• bleach work surface
• wash hands

Question 22

How do you minimise entry if unwanted bacteria to Petri dish

Answer 22

Only open Petri dish a small amount for a limited time

Question 23

Why do you incubate bacteria culture in a school lab at 25 degrees

Answer 23

To stop human pathogens growing as human bacteria/pathogens grow at 37 degrees

Question 24

What is the total count of bacteria

Answer 24

Total count counts both living and dead bacteria (over estimate)

Question 25

What is the viable count of bacteria

Answer 25

Viable counts only living bacteria (underestimate)

Question 26

What do you need to do to count bacteria

What assumptions do you make?

Answer 26

You must count using serial dilution

Assumption: one cell gives rise to one colony, this can create an underestimate if bacteria due to possible clumping

Question 27

What 3 things do you need to know to estimate total number of bacteria

Answer 27

1. Colony number
2. Dilution factor
3. Volume of sample

Question 28

How do you pick which colony number to used

Answer 28

Pic the highest value of countable non clumped colonies

Question 29

How do you calculate dilution factor

Answer 29

Total volume in the tube/volume added to the tube

Question 30

What are the 2 most commonly used dilution factors

Answer 30

x10 and x100

Question 31

How do you calculate the multiplication value

Answer 31

1/sample volume

Question 32

Equation to estimate the value of bacteria in the original sample

Answer 32

Colony number x dilution factor x sample volume multiplication factor

Question 33

Name the 3 types of bacteria

Answer 33

Coccus (circular)
Bacillus (cylindrical)
Spirillum (spiral)

Question 34

Name the 4 stages in the population growth graph

Answer 34

Lag phase
Log phase
Stationary phase
Death phase

Question 35

Why is there a low rate of population growth in the first 3 hours of the experiment

Answer 35

Take time for the digestive enzymes to be produced, nutrients to be digested, protein synthesis to occur and genes for the production of specific enzymes to be switched on/ off.