Topic 6

Question 1

kw. Nutrient medium

Answer 1

substance used for the culture of microorganisms in either liquid or solid form

Question 2

kw. Nutrient broth

Answer 2

liquid nutrient for culturing microorganism, commonly used in flasks , test tubes or bottles

Question 3

kw. Nutrient agar

Answer 3

Jelly extracted from seaweed and used in a solid nutrient for culturing microorganism

Question 4

kw. Selective medium

Answer 4

Growth medium for microorganisms containing a very specific mixture of nutrients. Only allowing one type of microorganism to grow on it

Question 5

kw. Innoculation

Answer 5

process by which microorganisms are transferred into a culture medium under sterile conditions

Question 6

Describe how aseptic techniques are used to transfer bacterial cells growing on an agar plate to a tube containing sterile broth

Answer 6

wash hands with distilled water

Disinfect bench with 1% Virkon

Light Bunsen Burner and work near the flame

sterilise the inoculation loop with the Bunsen flame and allow it to cool down

use sterile loop to transfer bacteria

open lid of the agar plate to a small extent to prevent other bacteria from falling on the plate

Incubate bacteria at under 37 *C to prevent bacteria with potential threat to humans being cultured

Question 7

Describe the use of Haemocytometers in counting cells

Answer 7

a thick microscope slide with a rectangular chamber that holds a standard volume of liquid, the chamber is engraved with grid lines

the sample of nutrient broth is diluted by half with an equal volume of trypan blue which stains dead cells blue

that way we only count the living cells (viable cell count)

we take measurements at time intervals calculation means for the 4 sets of 16 squares

one set of 16 squares= number of cells x 10 ^4 per cm^3 of broth

Question 8

Describe the use of Optical methods in counting cells

Answer 8

AKA turbidimetry

as the no. of bacterial cells in a culture increases, it because more turbid (cloudy) so it absorbs more light meaning less passes through

calorimeter measures absorbance and thus the number of microorganisms

calibration curve can be produced by growing a control culture taking samples at regular time intervals. the turbidity of each sample is measured and a cell count using a haemocytometer is made.

relationship between turbidity and no. of bacterial cells

this curve can be used to measure the no. of microorganisms using turbidimetry

Question 9

describe the use of dilution plating in counting the number of cells

Answer 9

is used to count the total number of viable cells

solid mass of microbial growth is often present after culturing making it impossible to count individual colonies

dilute original culture in stages until a point where colonies can be counted

Question 10

kw. Generation time

Answer 10

the time span between bacterial divisions

Question 11

kw. lag phase

Answer 11

the time the bacteria is adapting to their new environment and are not yet reproducing at their maximum rate

Question 12

kw. log phase

Answer 12

the time when the rate of bacterial reproduction is close to or at its theoretical maximum repeatedly doubling in a given period

Question 13

kw. stationary phase

Answer 13

when the total growth rate is zero as the number of new cells formed by binary fission is equalled by the number of cells dying due to factors including competition for nutrients
lack of essential nutrients
accumulation of toxic waste products
Oxygen

Question 14

kw. death phase

Answer 14

When reproduction has almost ceased and the death rate of cells is increasing so that the population number falls

Question 15

kw. endotoxins

Answer 15

lipopolysaccharides that are an integral part of the cell wall of gram negative bacteria

Question 16

kw. exotoxins

Answer 16

soluble proteins that are produced and released into the body by bacteria as they metabolise and reproduce in the cells of their host