Microbiology Flashcards

Question

What is the stationary phase for microorganisms?

Answer 1

- population has reached carrying capacity = limiting factors are preventing further cell division - less glucose and less amino acids, less ions and less O2 - rate of cell division = rate of cell death

Answer 2

- limiting factors are causing the population size to decrease - production of the toxin ethanol means toxins have accumulated - no glucose, amino acids, ions, oxygen - rate of cell death > rate of cell division

Answer 3

- birth rate in rabbits, whereas rate of cell division in yeast - lag phase could involve waiting for rabbis to reach sexual maturity - isolated small populations of rabbits reduces interbreeding, lowering the levels of genetic diversity (smaller gene pool)

Answer 4

- sterilising all media and equipment before use (flame inoculating loop) - flaming neck of culture bottle before opening and closing - lighting a Bunsen burner to the safety flame to create a convection current - don’t place cap of culture bottle on workplace = hold in hand - disinfect workbenches before and after (3% Lysol)

Answer 5

- sterilise workbenches before and after contamination with a disinfectants (3% Lysol) - lift lid of agar plate only to 45 degrees - seal agar dishes with tape, not the whole way round (prevents dangerous anaerobic bacteria growing) - flame neck of culture bottle without placing cap on the workbench

Answer 6

USING AN AUTOCLAVE - sealed vessel - heat to 121 degrees C - steam - high pressure - 15 minutes

Answer 7

GAMMA IRRADIATION - disposed of in biohazard waste bin

Answer 8

1) pass metal inoculating loop through a flame until red hot, allow to cool 2) holding bacterial culture bottle in one hand, remove the cap with the little finger of the other hand, placing next to the culture bottle in the first hand 3) flame the neck of the culture bottle for 2-3 seconds and then dip the inoculating loop into the culture 4) lift the Petri dish lid by 45 degrees, and using the inoculating loop, streak the bacterial culture across the agar 5) secure the lid onto the Petri dish with adhesive tape, but not completely sealing it (avoid anaerobic conditions that could promote the growth of pathogenic bacteria) 6) incubate at a suitable temperature (25 or 37 degrees C) for 24-48 hours 7) sterilise all equipment after use with either an autoclave or by using gamma irradiation

Answer 9

The amount of living and dead cells in a bacterial sample Can be performed with a haemocytometer = allows number of cells in a specific volume o be counted by counting a cell if it is in the centre of a square, or if it touches the top or left line

Answer 10

The number of living cells in a known volume of liquid medium Can be measured by a serial dilution

Answer 11

It assumes that a single bacterial cell will reproduce asexually to form a visible colony on an agar plate. The number of colonies represents the number of bacteria in the original undiluted sample

Answer 12

1) place 9cm3 of sterile distilled water into 5 sterile test tubes using a sterile pipette 2) place 1cm3 of the original bacterial culture into the first test tubes and gently mix (the culture has now been diluted 10x) 3) transfer 1cm3 of this dilution into the next test tube and gently mix (culture is now 100x diluted) 4) repeat this procedure for the remaining tubes 5) transfer 1cm3 of each diluted sample onto a sterile nutrient agar plate and use a sterile spreader to evenly distribute the sample onto each plate 6) repeat twice to get 3 samples per dilution so a mean colony number can be calculated 7) seal each agar plate with tape (not the whole way around) and incubate at 25 degrees for 24-48 hours 8) after incubation, identify the dilution with distinct, non merging colonies and count them 9) multiply this by the dilution factor to give the number of bacteria in the original 1cm3 bacterial culture sample

Answer 13

The colonies might merge (clumping) so counting may be inaccurat, resulting in an underestimate of cell numbers

Answer 14

There will be too few colonies on each plate to count to be statistically sound (leads to inaccuracies)

Answer 15

Using a colorimeter to measure the turbidity (cloudiness) of a culture as cell numbers increase Bacterial population measurements are measured by finding the absorbance value of the suspension and referencing a standard graph of light absorbance plotted against the number of bacterial cells TOTAL CELL COUNT = colorimeter cannot differentiate between living and dead cells

Microbiology Flashcards

(39 cards)