culturing microorganisms and aseptic technique

Question 1

what do microbes need to grow

Answer 1

source of carbon e.g. glucose for respiration
source of nitrogen e.g. ammonia to make amino acids

Question 2

what are the 2 types of growth medium

Answer 2

nutrient broth (kept in flasks and stoppered)
nutrient agar (a set jelly that can be poured into a Petri dish)

Question 3

summarise the key steps to take when working aseptically

Answer 3

was hands
disinfect the working atrea
have a bunsen flame on
as you open a flask pass the neck of the bottle over the flame (and when closing)
so not lift lid off Petri dish completely
pass glassware and metal equipment through the flame and dip in ethanol

Question 4

why wash hands

Answer 4

kill any bacteria and fungi

Question 5

why disinfect working area
with what

Answer 5

kills microorganisms on the surface
use virkon

Question 6

why have bunsen on

Answer 6

causes air to rise and prevents air borne microorganisms from settling
creates an area of sterile air around working area

Question 7

why pass bottleneck through flame

Answer 7

prevents bacteria entering by pushing air out of the flask

Question 8

why not lift lid off Petri dish completely

Answer 8

reduces chance of unwanted microorganisms from entering plate

Question 9

3 steps when growing microbes on agar plates

Answer 9

sterilisation
inoculation
incubation

Question 10

growing microbes on agar plates: describe sterilisation

Answer 10

heat an abundance of agar to 120C to sterilise it
allow agar to cool and pour it into a sterile Petri dish
leave lid on Petri dish

Question 11

growing microbes on agar plates: describe inoculation

Answer 11

introducing microorganisms to the growth medium
(heat inoculation gloop in blue bunsen flame and dip in ethanol, remove cap from broth culture and flame mouth of bottle, dip cool sterile inoculating loop in bottle, flame and recap bottle)

Question 12

inoculating techniques list

Answer 12

streaking
seeding
spreading
cotton bud

Question 13

describe inoculation by streaking

Answer 13

a wire inoculating loop is used to transfer a drop of liquid broth to the agar and drop is drawn out by dragging loop

Question 14

describe inoculation by seeding

Answer 14

a sterile pipette is used to transfer a top of liquid to the agar surface

Question 15

describe inoculation by spreading

Answer 15

sterile glass spreader is used to spread a drop of broth over surface

Question 16

describe inoculation by cotton bud

Answer 16

small cotton bud moistened with distilled water used to collect microorganisms from a surface and introduced to agar

Question 17

incubation steps

Answer 17

label and tape but don’t seal
place upside down
place at an appropriate incubation temp
view colonised through petri dish

Question 18

why do you label and tape

Answer 18

reduced chance of airborne contamination

Question 19

why do you not seal

Answer 19

prevent the formation of anaerobic bacteria which may be pathogenic

Question 20

why do you place Petri dish upside down

Answer 20

less chance of airborne particles landing on it and causing contamination
prevent accumulation of water (product of aerobic respiration) condensation that could disturb or compromise a culture

Question 21

why do we not incubate at 37C in schools

Answer 21

less risk of culturing microbes that are pathogens to humans (37C is body temp)

Question 22

why incubate at 25C

Answer 22

optimum temp for binary fission

Question 23

why view colonies through the petri dish

Answer 23

do not take lid off Petri dish as bacterial/fungal spores may be produced and could spread

Question 24

what can broths be used for

Answer 24

increasing the population sixes of bacteria before plating
investigating the rate of population growth

Question 25

how do you know when bacteria have grown in a broth

Answer 25

broth turns cloudy
colonies can take a variety of shapes, sizes and colours