22.6 Culturing microorganisms in the lab

Question 1

what is culturing?

Answer 1

growing large numbers of microorganisms to view

Question 2

what are the dangers of microorganisms?

Answer 2

risk of mutation could make microorganism pathogenic

contamination with pathogenic microorganisms from the environment can make it pathogenic too

Question 3

what are the conditions which need to be controlled when culturing microorganisms?

Answer 3

nutrients available
temperature
oxygen
pH

Question 4

how is food provided for a microorganism?

Answer 4

in a nutrient medium

Question 5

what are aseptic techniques?

Answer 5

used to prevent contamination of cultures by unwanted microorganisms

Question 6

what is wrong with contaminated cultures?

Answer 6

give imprecise results
can be hazardous to health
can lead to entire batches being ruined (costly)

Question 7

how is broth inoculated?

Answer 7

make suspension of bacteria

mix suspension with sterile nutrient broth in a flask

stopper the flask with cotton wool to prevent air contamination

incubate at suitable temperature and shake regularly to provide oxygen for bacteria

Question 8

why is a broth shaken when inoculating?

Answer 8

to provide oxygen for the bacteria to grow

Question 9

how is agar inoculated?

Answer 9

inoculate the inoculating wire loop by holding it over a bunsen flame

do not allow loop to touch ANYTHING

inoculate the lid of the bacteria container

dip sterilised loop into bacteria

make zig zag streak on the agar plate using the loop

add lid to petri dish and tape shut

DO NOT completely seal, allow for some oxygen to enter

incubate

Question 10

why is oxygen need to be allowed into petri dish?

Answer 10

to prevent anaerobic bacteria from forming

Question 11

what other precautions needed to prevent contamination?

Answer 11

work near a bunsen flame

minimise the time the agar plate is opened

use a lab coat and tie up hair

Question 12

why should you work near a bunsen flame?

Answer 12

allows hot air to rise which draws any unwanted microorganisms away from culture

Question 13

why are logarithmic numbers used to represent bacteria population in a growth curve?

Answer 13

differences between the number of organisms from the initial number are too large to show on graph

Question 14

what are the four stages of bacteria growth in a closed system?

Answer 14

lag phase
log phase
stationary phase
death phase

Question 15

what is a closed culture and what affect does it have on growth?

Answer 15

when growth occurs in an external vessel which is isolated from the environment

means that extra nutrients aren’t added and waste products aren’t removed

thus prevents growth when competition increases and food becomes scarce

Question 16

lag phase

Answer 16

bacteria are adapting to their new environment so are growing and producing the enzymes needed

NOT reproducing at their maximum rate

Question 17

log phase

Answer 17

population size increases quickly as the culture conditions are at their most favourable for reproduction

lots of food and little competition so growth maximised

close to MAXIMUM rate of reproduction

Question 18

stationary phase

Answer 18

carrying capacity is reached with the death and reproductive rate being equal

more competition and less food means growth is prevented

build up of toxic waste and lack of food leads to death of microorganisms

Question 19

death phase

Answer 19

death rate much greater than reproductive rate

food is scarce and waste products are TOXIC

therefore more death of microorganisms

Question 20

what are the limiting factors which prevent exponential bacteria growth?

Answer 20

nutrients available
oxygen levels
temperature
build up of waste
change in pH

Question 21

nutrients available

Answer 21

at first there is A LOT of food
then as bacteria multiply exponentially then food is used up

eventually nutrients are no longer available and so growth and reproduction stops

Question 22

oxygen levels

Answer 22

as population increases, the demand for oxygen increases

oxygen levels end up limiting

Question 23

temperature

Answer 23

enzyme controlled reactions in microorganisms are affected by the temperature

high temp will speed reactions up

BUT temp too high then enzymes denature and microorganisms die

Question 24

build up of waste

Answer 24

as bacteria numbers rise, toxic material also rises which can poison and kill microorganisms

Question 25

change in pH

Answer 25

increase in CO2 production from respiration decreases the pH which affects enzyme activity

inhibits population growth