3.4 microbiology

Question 1

What are sphere shaped bacteria called?

Answer 1

Cocci (one is coccus)

Question 2

What are rod shaped bacteria called?

Answer 2

Bacilli (one is bacillus)

Question 3

what are spiral shaped bacteria called?

Answer 3

spirilli (one is spirillum)

Question 4

Things that are common to gram+ve bacteria:

Answer 4

. walls with a thick layer of peptidoglycan
. no outer lipopolysaccharide layer
. stains purple
. spherical cocci shape

Question 5

Things that are common to gram-ve bacteria:

Answer 5

. thinner layer of peptidolycans
. does contain outer lipopolysaccharide layer
. stains red
. bacilli rod shaped

Question 6

conditions for for growth of bacteria:

Answer 6

. nutrients such as glucose nitrogen vitamins mineral salts
. temperature- growth regulated by enzymes

Question 7

conditions for growth of bacteria:

Answer 7

PH- alkaline conditions
Oxygen-
obligate aerobes- microorganisms that must have oxygen for metabolism
facultative aerobes- microorganisms that can grow with or without oxygen (but they grow better in oxygen)
obligate anaerobes- microorganisms that will only grow in the absence of oxygen

Question 8

What does total count mean?

Answer 8

include both living+dead cells

Question 9

What does viable count mean?

Answer 9

count only living cells

Question 10

What does autoclave do and the conditions?

Answer 10

.dispose of bacterial culture plates
.at 121 degrees for 15 mins

Question 11

How do you carry out a viable count?
(using the serial dilution and agar plates)

Answer 11

• take sterile agar plates (however many tubes there are)
• transfer said amount cm3 of each to separate plate
• spread with sterile spreader
• incubate plates at suitable temp 25degrees
• count colonies 1 colony= 1 cell

Question 12

How to work out the dilution factor?

Answer 12

for example: you put in 0.1cm of the stock solution in the test tube that has 9.9cm3 of water in it
then you do 0.1/(0.1+9.9)= 10 to the minus two

Question 13

Why did we work near the bunsen in the bacteria colony experiment?

Answer 13

• working in the updraft
• convection current carries bacteria + fungal spores away from plates preventing contamination

Question 14

why are the plates never sealed in the experiment?

Answer 14

maintain aerobic conditions- prevent growth of anaerobic human pathogens

Question 15

Why incubate plates at 21 degrees in experiment?

Answer 15

prevent growth of human pathogenic bacteria

Question 16

If there’s a small amount of colonies on plate what can we say?

Answer 16

not enough colonies to count to make a reliable estimate of concentration

Question 17

If there’s too many colonies on plate what can we say?

Answer 17

too many colonies to count/ overlap therefore we cannot make a reliable estimate of concentration

Question 18

If there’s just enough colonies on the plate what do we say?

Answer 18

enough colonies that don’t overlap to make a reliable estimate of concentration

Question 19

to calculate number of colonies in original sample:

Answer 19

no of colonies x dilution factor(POSITIVE) divided by volume put on plate