RP 3- investigating water potential

Question 1

what are calibration curves?

Answer 1

Calibration curves ​​are ​graphs​​ used to ​determine an unknown concentration​​ of a sample, in this practical potato

Question 2

how do you produce a calibration curve?

Answer 2

by comparing the unknown to a set of standard samples with known concentrations

Question 3

what is a dilution series?

Answer 3

can be used to create a set of samples with known concentrations.

Question 4

what is step 1 of this practical? (2)

Answer 4

1) Make a ​series of dilutions​​ ​​of 1M sucrose solution. These should be at ​0.0, 0.2, 0.4, 0.6, 0.8 and 1.0M sucrose​​2) Dilute using ​distilled water.

Question 5

what is step 2 of this practical?

Answer 5

Measure 5cm3​ o​f each dilution into separate test tubes.

Question 6

what is step 3 of this practical? (2)

Answer 6

1) Use a cork borer to cut out six potato chips and cut down the sections into identically sized chips​​
2) Dry each chip using a paper towel to remove excess water but do not squeeze.

Question 7

what is step 4 of this practical?

Answer 7

Weigh each​​ potato before the start of the experiment

Question 8

what is step 5 of this practical?

Answer 8

Place a potato chip in each test tube (one per sucrose concentration) and leave for ​20 minutes

Question 9

what is step 6 of this practical? (2)

Answer 9

1) Remove each potato chip, dry gently using paper towel
2) weigh them in turn​

Question 10

what is step 7 of this practical?

Answer 10

Calculate the​ ​​percentage change in mass ​​for each sucrose solution​

Question 11

how do you plot the graph? (3)

Answer 11

1) Plot a graph of ​change in mass ​​against​ concentration of sucrose solution​​.
2) The point at which the line of best fit ​crosses the x axis ​​(zero change in mass) indicates the point at which the solution is ​isotonic​​.
3) This is when the water potential of sucrose solution is the same as the water potential of the potato tissue, so there is ​no net movement of water in or out​​ of the potato.

Question 12

what are the conclusions from this practical? (4)

Answer 12

1) Potato chips in ​lower concentrations ​​of glucose solution will ​increase in mass​​
2) potato chips in ​higher concentrations​​ of glucose solution will ​decrease in mass​​.
3) In the ​dilute glucose solutions​​, the solution has a higher water potential than the potato, so water ​passively​​ moves via ​osmosis​​ to the area of lower water potential (the potato). This causes the potato to ​increase​​ in mass.
4) In ​concentrated glucose solutions​​, water will move ​out​​ of the potato, thus the potato will ​decrease​​ in mass.