Qualitative: Activity of Immobilised Enzymes
Invertase
Breaks down sucrose into glucose and fructose
Yeast cells make invertase
Invertase is a reducing sugar
Tests for biological molecules:
Benedict's - blue to red/orange precipitate
Biuret- blue to lilac
Why do we need to test for the presence of protein?
Skills:
similar size beads
columns filled to same level
columns left for same length of time before
opening the tap
Limitations of Benedict's:
does not test for other reducing sugars/only indicates the presence of glucose
not sensitive enough
colour comparison is subjective
if the time given is not long enough, it can give incorrect results
Advantages of having an immobilised enzyme only:
more product
no contamination by yeast
no sugar is used by the yeast for respiration
Advantages of having immobilised yeast:
little loss of enzyme
enzyme stays inside the yeast cell
don't have to extract the enzyme from the yeast
using a whole organism is cheaper
Quantitative task - Effect of NaCl on Activity of Yeast Cells:
0% - 20% NaCl When would you expect yeast to be most and least active?
If results from 5-20% are similar, how might you explain it?
If yeast remain active, what does this indicate about their tolerance of NaCl?
Which concentration of salt would you expect them to be most and least tolerant
of?
Evaluative Task: Effect of NaCl on Activity in Yeast (0-20% NaCl)
Skills task - identification of how table should be laid out
Consider the following table showing the results of an unrelated experiment - the
effect of humidity on the rate of transpiration:
Distance moved by air
bubble
5.2cm
Humidity
2.9cm
1%
15mm
5%
2mm
10%
0cm
20%
none
Identify all the things wrong with the above table
Carbon dioxide can be made by yeast cells both aerobically and anaerobically
How do you think NaCl affects the rate of respiration? Think Unit 4!
Considering the answer to the above, why would you leave the yeast for several minutes
before collecting data?
to allow time for the NaCl to affect the proteins/respiration/yeast
to allow time for the yeast to reach the desired temperature/30 degrees
The experiment required students to record the distance moved by yeast suspension up
to a maximum of two minutes. Why would recording the volume of gas be an
improvement?
gas could be collected over a longer time
What would you expect the control to be in this experiment?
What would you expect to happen to the pH during the experiment? Think back to AS
Transport in Animals/respiration
Explain why scientists do replicates:
increase reliability
more easily identify anomalies
make comparisons more valid
enable us to undertake statistical tests
Explain the osmotic effect of NaCl - use AS knowledge!:
reduces water potential
water diffuses out of yeast cells
down the water potential
stops the yeast cell working/stops reactions
If NaCl affects the proteins involved in respiration, what type of protein might this be?
enzyme/sodium:potassium pump/protein channel
What level of protein structure would these be and what can you remember about this
level of protein from AS knowledge?
Tertiary/globular/3D/coiling of alpha-helix/ionic bonds