58.........Practical work
22. Determination of the rate of anaerobic respiration
Many yeasts of the genus Saccharomyces
are facultative anaerobes. In the absence of
oxygen, yeasts convert glucose into ethanol
and carbon dioxide. The rate at which
carbon dioxide is produced can be used as a
measure of the overall rate of anaerobic
respiration.
Procedure
1.
Thoroughly mix the suspension of
yeast cells by shaking. Pipette 10 cm3
of this suspension into a beaker.
Introduce 20 cm3 of a substrate
solution (e.g. 4% glucose solution) into
the beaker. Mix well.
2.
Introduce 10 cm3 of the glucose-yeast
mixture into a 10 cm3 syringe.
3.
Clamp the filled syringe at a height of
35-40 cm above the bench surface.
4.
Use a 2 cm long rubber tubing to
connect a capillary tube of about 20 cm
long and the nozzle of the syringe, as
shown in Fig.1.
5.
Apply pressure gently to the plunger of
the syringe until a meniscus appears
near the upper end of the capillary
tube. Mark the position of this
meniscus. As carbon dioxide is
evolved during fermentation of
glucose, each bubble of gas will
displace an equivalent volume of the
mixture into the capillary tube.
Fig.1 Experimental set up
Practical work.........59
6.
At intervals of 15 minutes, over a
period of 90 minutes, mark the
respective positions of the meniscus.
7.
Plot a graph showing the distance
moved by the meniscus against time.
From the graph, calculate the rate of
anaerobic respiration.
8.
Set up a control using water instead of
glucose-yeast mixture.
Note
1.
Yeast powder purchased from
supermarkets are good materials for
this experiment.
Material
1. Preparation of yeast suspension
•
Add 10 g dried yeast to 100 cm3 of cooled boiled water.
•
Activate the yeast by adding a teaspoonful of glucose and allow the mixture
to stand for two hours in a beaker covered with cellophane.