Bio Practicals

Question 1

What does haemocytometry measure?

Answer 1

Total cell count

Question 2

Preparation of a haemocytometry plate

Answer 2

• Well mixed cell culture sample is first diluted
• Then introduced to the central chamber via pipette
• Liquid flows under cover slip
• Sample viewed under microscope and no. of organisms in several squares is counted
• Average is calculated, multiplied by dilution factor gets you an estimate of the original number in the sample

Question 3

Turbidimetry measures

Answer 3

Total cell count

Question 4

Turbidimetry is measured using

Answer 4

Colorimeter

Question 5

Turbidmetry preparation

Answer 5

• Culture sample is aseptically removed and thoroughly mixed before being placed in a cuvette.
• Cuvette is placed in the colorimeter and the optical density is measured as % absorbance.
• More cells present = greater turbidity

Question 6

Cons of turbidmetry

Answer 6

Cannot distinguish living cells from dead cells

Cannot distinguish cells from particles of matter in the culture medium

Question 7

To avoid inaccuracy created by particles of matter from the medium affecting the percentage absorbance, what precaution is taken?

Answer 7

Colorimeter is set to zero using a ‘blank’ cuvette which contains the culture medium alone

Question 8

What does dilution plating measure

Answer 8

Viable counts

Question 9

Methods of sterilisation

Answer 9

• Direct heat - inoculating loop, neck of tubes
• Autoclaving (120) - glassware, unwanted cultures
• Burning alcohol - quick sterilisation of glass
• Disinfectants - inanimate objects, e.g. Wood surfaces

Question 10

Bioassay

Answer 10

Enables the effectiveness of a compound (antibiotic or disinfectant) to be determined by its effect on the growth of a microorganism

Question 11

What can bioassays be used to screen and how

Answer 11

Microorganisms to determine if they produce an effective antibiotic.
Achieved by measuring their ability to inhibit the growth of bacteria on a bacterial lawn.

Question 12

What does the diameter increase of a fungal mycelium measure?

Answer 12

Growth of filamentous fungi

Question 13

Increase in dry mass measures

Answer 13

Growth rate of a variety of microorganisms

Question 14

Problems with ORS containing more glucose

Answer 14

Lowered the water potential in the lumen of the small intestine cause diarrhoea to worsen

Question 15

What polysaccharide is present in ORS and why

Answer 15

Starch as it is osmotically inactive and insoluble
It also is slowly broken down by amylase and maltose into glucose
This mean it can be taken up by co-transport at a normal rate

Question 16

Ideal scientific trial for medicines

Answer 16

• Large sample size
• Random split of subjects into two groups
• One group receives medicine, the other a placebo
• Mean results compared

Question 17

Medical testing with ORS

Answer 17

• sample must all suffer from diarrhoea
• Subjects are typically children at risk of death
• It is unethical and unacceptable to conduct trials ‘scientifically’