Required practical 3 - water potential in plant tissue

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What is the independent variable?
Concentration of solution (usually sucrose)
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What is the dependent variable?
Change in mass of potato/plant tissue.
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Why is the change in mass expressed as a ratio (% change in mass)?
Allows for direct comparison of changes in mass between different pieces of potato (as the pieces may not all be exactly the same size initially).
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What must be prepared to obtain solutions of varying concentrations?
A dilution series.
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What is used to cut cylinders of potato?
A cork borer
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Why must the potato pieces be blotted dry before the initial weighing?
So that their initial weighed mass was not affected by any water on the outside of the potato - this mass of water may be different on different potatoes.
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What are the controlled variables?
Potato used, time left in each solution, temperature (use a water bath), size of potato cylinders.
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Why are the potato pieces blotted dry before the final weighing?
So that the change in mass is not affected by the mass of water on the outside of the potato pieces. This extra mass is not a systematic error - the mass of water on each potato cylinder will not be the same.
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How is % change in mass calculated?
(change in mass/original mass)x100
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What is plotted on each axis of the graph?
% change in mass on the y - axis and conc. of solution on the x - axis.
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How is the water potential of the potato tissue identified?
Where the line on the graph crosses the x - axis (conc. at which the % change in mass is 0)
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What units are water potential measured in?
KPa (kilopascals)
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What formula can be used when producing a dilution series?
M1xV1 = M2xV2, where M1=conc. of initial solution, V1=vol. of initial solution needed, M2=conc. required, V2=vol. of final solution.
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Why are all pieces taken from the same potato?
As the tissues of different potatoes may have different water potentials.
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Why are the potato skins removed?
They are waterproof (waxy cuticle) and will therefore prevent osmosis - which is required to obtain valid results.
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Why should the potato cylinders all have roughly the same dimensions?
So that they have the same surface area and therefore differences in surface area do not result in differences in the rate/amount of osmosis (only affected by conc. of solution).
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Other cards in this set

Card 2

Front

What is the dependent variable?

Back

Change in mass of potato/plant tissue.

Card 3

Front

Why is the change in mass expressed as a ratio (% change in mass)?

Back

Preview of the front of card 3

Card 4

Front

What must be prepared to obtain solutions of varying concentrations?

Back

Preview of the front of card 4

Card 5

Front

What is used to cut cylinders of potato?

Back

Preview of the front of card 5
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