CPAC 12-

Question 1

What are the aseptic techniques?

Answer 1

• wipe down surfaces with antibacterial cleaner before and after experiment
• use a Bunsen burner in the work space so that convection currents draw microbes away from the culture
• flame wire loop before using to transfer bacteria
• flame neck of bottle before use to prevent bacteria entering
• keep all vessels containing bacteria open for minimum amount of time
• close windows and doors to limit air currents

Question 2

Give the steps to make the glucose solution in this practical

Answer 2

use a sterile clear sided 500cm3 conical flask of 250cm3 of 0.5% glucose concentration
should be stoppered with cotton wool and contain sterile stirring flea

Question 3

Outline the practical stages of this reaction

Answer 3

• fill cuvette with glucose culture medium to set the absorbance of the colorimeter to zero
• fill measuring cylinder with yeast suspension, transfer to cuvette and measure the absorbance
• put the sample back into the yeast suspension
• repeat steps 1 and 2 at least 5 times over 12 hours
• record absorbance and the time
• use haemocytometer to relate colorimetry readings to direct cell count
• stain yeast suspension with methlyene blue, add a drop to the slide and count visible cells