Practical Bio-effect of alcohol concentration on the leakage of pigment from beetroot cells.

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You were provided with beetroot discs that were washed thoroughly before the start of
the investigation. Explain why it was important to wash the beetroot discs.
To wash off any pigment / betalins (on the discs);
To show that any pigment released is from the effect of alcohol;
n Part 2 of this investigation you used five concentrations of alcohol.
2 (a) Describe a suitable control for your investigation
(Distilled) water and (two) discs of beetroot;
Explain why this control would be necessary
To show that the alcohol was causing the leakage of pigment /
to compare it with the effects of the alcohol;
Explain why you were instructed to shake the test tubes every minute (step 11).
Increase the contact of all surfaces with the alcohol / prevent discs
sticking together / maintain a diffusion gradient for the pigment;
Explain why you were instructed to pour the alcohol immediately from the
experimental test tube into a clean test tube (step 12).
To limit the variation in time discs are in alcohol / make sure Accept fair test if
all the discs were in contact with alcohol for the same length of time / qualified by relevant
so no more pigment can diffuse out of the discs;
You were given discs taken from fresh beetroot in your investigation.
Explain why your results would have been different if you had used cooked beetroot.
Heating / cooking would damage the (plasma) membranes; Do not accept reference
Valid explanation of damage e.g. disrupts phospholipid to killing membrane
bilayer / denatures proteins;
A lot of pigment released during cooking / less pigment present
(in tissue);
You used a water bath in this investigation. Explain why a decrease in temperature of
5 °C would affect the results
Less kinetic energy;
Molecules move slower;
Lower rate of diffusion;
Membranes less fluid;
Two students carried out the same investigation as you did. They worked in the same
practical session and followed the same procedure. They worked accurately but
found their results were different. Suggest one reason for this.
Variation in beetroot / variation in judging colour;
The student started drawing his curve from the origin, was he correct to do this?
Explain why
No (no mark)
Curve drawn on graph should not extend beyond data collected / no
control carried out with water;
Phospholipids dissolve in alcohol.
Explain the shape of the curve between alcohol concentrations of 40 % and 80 %
Phospholipids are in the membranes;
Membrane breaks down faster / more at higher concentration of alcohol /
(higher concentration of alcohol) increases the permeability of
membranes;
More betalins / pigments move out of cells / vacuoles;
(Allows) faster rate of diffusion of pigment;
The student suggested that point A on the graph was an anomaly. What should he do
to check this?
Repeat experiment at 100 % alcohol concentration;
Check to see if results are concordant / similar;
After further investigation the student found the point was not an anomaly.
Suggest why the curve levels out.
Concentration of pigment inside and outside of the tissue reached Do not accept all
equilibrium / an equal concentration of pigment inside and outside the pigment has
beetroot / pigment diffusing in and out at the same rate; diffused out
Maximum membrane damage
Use the information in Figure 1 to explain two ways in which fatty acids are important
in the formation of new cells.
Fatty acids used to make phospholipids;
Phospholipids in membranes;
More phospholipids more membranes made; 2 max
Fatty acids respired to release energy; Do not allow credit for
More triglycerides more energy released; 'making' energy
Energy used for cell production / production of named cell component;
The concentration of omega-3 fatty acids in milk changed when cows were fed on
corn instead of grass. Describe how
(Omega-3 concentration) falls more rapidly at first;
Levels out at 140 days / concentration of 0.4 %;
Calculate the rate of decrease in the mean omega-3 fatty acid concentration between
0 and 40 days.
Show your working
Two marks for correct answer of 0.04 or 0.043;;
One mark for incorrect answer which clearly identifies total fall of 1.7;
The omega-3 fatty acid concentration is expressed as a percentage of total fat.
Explain the advantage of this
To take into account variation in fat content of milk /
fat content varies from cow to cow; 2
Allows comparison;
One farmer concluded from the graph that feeding cows on corn reduces the
omega-3 fatty acid content in milk. Evaluate this conclusion
The graph shows a decrease with time feeding on corn;
No control group;
Might have fallen anyway / might decrease with time rather than with
time spend feeding on corn;
Other factors / other named factor might also have changed;
Only one investigation so might not be representative;
It is not possible to conclude from the data that the concentration of omega-3 fatty
acids in the farmed salmon is higher than that of the wild salmon. Use the data to
explain why
Standard deviation shows there is overlap of the 2 data sets;
Small sample of wild salmon so may not be representative of
population
There is a difference between the concentration of omega-3 fatty acids in the wild
trout and trout farmed in cages. Suggest two causes of this difference.
The different diet of the fish;
Omega-3 fatty acids used in respiration / as a source of energy;
Wild trout are more active / use more energy;