21. Extra Knowledge: Including Section C Tips

Question 1

when drawing graphs on cell growth, what should you do with the y axis for cell concentration

Answer 1

log it

calculator - press ‘log’ button and type in value after to find the log

Question 2

microbial growth:

lag phase

Answer 2

no increase in cells - here bacteria are adjusting to the environment

Question 3

what follows lag phase, what is this

Answer 3

log phase:

exponential increase in number of living cells

Question 4

what phase follows log phase, describe?

Answer 4

stationary phase

- insufficient nutrients to sustain rapid growth = growth plateus

Question 5

what is the final stage of microbial growth

Answer 5

death phase

exponential decrease in number of living cells

Question 6

why is there a death phase

Answer 6

waste products build up = toxic

insufficient nutrients to maintain metabolism

Question 7

how do you establish specific growth rate

Answer 7

draw tangents to lag phase, stationary phase and exponential phase

determine the points the exponential phase tangent crosses the stationary and lag points

B1 = lag & exponential
B2 = stationary & exponential 
T = time between B1 and B2

(B2-B1) / T = specific growth rate

Question 8

using specific growth rate calculate doubling time

Answer 8

(LN2)/ specific growth rate

Question 9

how can u use an autoclave to sterilise contagious lab sample

Answer 9

uses steam under pressure to destroy pathogens for a given amount of time

Question 10

what 3 methods can be used to sterilise lab samples

Answer 10

autoclave
bringing the medium to a boil
disinfection using chemicals such s chlorine

Question 11

how many micrometers in a millimeter

Answer 11

1000

Question 12

how many microlitres per 1000 nanolitres

Answer 12

1

Question 13

what is 1 mm3 in nanoliters

Answer 13

1000

Question 14

how many micrometers in 1 cm3

Answer 14

1000

Question 15

why do CFUs and cell counts give different values

Answer 15

CFU = count of only viable cells

cell count = count of all cells both living and dead

Question 16

when calculating colony forming units what is the important first step

Answer 16

convert the volume into the one the answer must be in the form of
(50 ul sample, find how many colonies in 1 litre - must first multiply by 20)

Question 17

is a colony has been diluted, what must be done when calculating colony forming units

Answer 17

divide the number of cells per stated volume by the dilution factor
e.g. 240 / 10^6

Question 18

describe the process of western blot

Answer 18

specific proteins in a blood or tissue sample are subject to gel electrophoresis

separated proteins are transferred out the gel and transferred to a membrane

membrane is exposed to specific antibodies that are tagged

used to diagnose disease DIRECTLY via antigens

Question 19

name 3 direct methods of diagnosis

Answer 19

visualising oocytes/ cysts under microscope
western blotting
ELISA

Question 20

name 2 indirect methods of diagnosis

Answer 20

sandwich ELISA

neutralisation assay

Question 21

what are the 6 stages of replication

Answer 21

attachment 
entry
uncoating
replication
maturation 
release

Question 22

how does PCR work

Answer 22

uses a thermal cycler to amplify genetic material

1. dsDNA is heated allowing separation of strands
2. as it cools, pathogen- specific primers anneal
3. taq polymerase is added to extend the DNA strand
   = repeated to amplify DNA fragments

there will only be amplification if the pathogen is present