6.1 bacteria (end lessons)

Question 1

What is the process in which bacteria use to divide?

Answer 1

Binary fission

Question 2

What is generation time?

Answer 2

The time between bacterial divisions

Question 3

What factors can limit reproduction of bacteria?

Answer 3

Nutrient availability
Space
Waste production

Question 4

What is the lag phase in bacterial growth?

Answer 4

this is where bacteria are adapting to their new environment and are not yet reproducing to they maximum rate.

Question 5

What is the log phase in bacterial growth?

Answer 5

rate of reproduction is close to the maximum.

Question 6

What is the stationary phase in bacterial growth?

Answer 6

total growth rate is zero as number of new cells formed by binary fission is equal to the number dying.

Question 7

What is the death phase in bacterial growth?

Answer 7

reproduction are almost stopped and cell death is increasing.

Question 7

Why does the exponential growth of bacteria not continue?

Answer 7

Reduction of nutrients
Build up of waste products inhibit further growth and even begin to poison cells. In particular, carbon dioxide will build up and change the pH of the culture to the point where growth can’t occur.

Question 8

What piece of equipment can be used to count individual bacterial cells?

Answer 8

A haemocytometer

Question 9

What stain can be used before using a haemocyctometer and what does it do that is significant?

Answer 9

Trypan blue
Stain dead cells blue so these can be easily discarded

Question 10

How is the quantity of fungi in a sample measured?

Answer 10

The area it covers is calculated

Question 11

What is turbidity?

Answer 11

A measure of how opaque a solution is

Question 12

How does a colorimeter work when measuring turbidity of a bacterial sample?

Answer 12

A colorimeter is used to shine light through a solution.
There is a sensor on the other side that can detect how much light has passed through the solution and how much has been absorbed.
Cloudier solutions absorb more light and less light reaches the sensor.
Solutions with less solute absorb less light and so more light reaches the sensor.

Question 13

What does enumerating bacteria mean?

Answer 13

To count bacteria

Question 14

When doing serial dilutions, how many colonies are ideal to count?

Answer 14

20-200

Question 15

How are dilutions helpful in counting bacteria?

Answer 15

Often in an undiluted culture, there are too many colonies to count. Dilutions mean a more manageable number, to get a more accurate count. A multiplication calculation can be carried out to work out the actual number in an undiluted sample.

Question 16

What do bactericidal antibiotics do?

Answer 16

Kill the bacteria

Question 17

What do bacteriostatic antibiotics do?

Answer 17

Inhibits bacterial growth but does not kill the cells

Question 18

What do sulfonamide antibiotics do?

Answer 18

Interrupt metabolic pathways such as blocking nucleic acid synthesis

Question 19

What do tetracyclines and chloraphenicol antibiotics do?

Answer 19

Protein synthesis inhibitors so protein production is affected.

Question 20

What do beta lactams such as penicillin do?

Answer 20

Cell wall agents, prevent formation of cross linking in cell walls so bacteria are killed by lysis

Question 21

What do cephalosporins do?

Answer 21

Damage the cell membrane of bacteria cells so water moves in, killing the bacteria

Question 22

Examples of bactericidal antibiotics.

Answer 22

Beta lactams (penicillins)
Cephalosporins
quinolone

Question 23

What do quinolone antibiotics do?

Answer 23

Stop bacterial DNA coiling up so it no longer fits in the cell

Question 24

Name ways in which antibiotics can affect bacterial cells.

Answer 24

Disrupting the cell membrane
Disrupting the cell wall
Disrupting metabolic pathways
Inhibiting RNA or DNA synthesis
Inhibiting protein synthesis

Question 25

In antibiotic practicals, What is the purpose of the ‘control disc’?

Answer 25

The control disc has been sterilised and soaked in distilled water. It should have no antimicrobial properties. This means if there is a clear area with no bacterial growth around the antibiotic disc, we know it must be because of the antimicrobial properties of the antibiotic disc.

Question 26

What is antibiotic resistance?

Answer 26

When bacteria evolve in response to exposure to antibiotics. They evolve to become resistant to antibiotics, meaning they are no longer affected by them.

Question 27

How does antibiotic resistance arise?

Answer 27

Bacteria mutate (changes to DNA), occasionally one of these mutations gives the bacterium an advantage meaning it is no longer killed by an antibiotic. This bacterium, survives, replicates and produces more antibiotic-resistant bacteria.

Question 28

What problems in real life can cause antibiotic resistance?

Answer 28

Use of incorrect dose of antibiotic
Not completing course
Use not appropriate for certain conditions
Not many new antibiotics are being developed

Question 29

State two differences between exotoxins and endotoxins.

Answer 29

Endotoxins are lipopolysaccharides but exotoxins are proteins.
Endotoxins are released from gram negative bacteria but exotoxins are released from both types of bacteria.
Effect of exotoxins takes longer

Question 30

Give two differences between Gram negative bacteria and Gram positive bacteria.

Answer 30

Gram positive have a thicker cell wall.
Gram positive stains purple with gram stain whereas gram negative bacteria doesn’t stain.