Required Practical 3 - Calibartion Curve of Dilution Series/Water Potential of Plant Tissue

Question 1

Suggest what a calibration curve is used for

Answer 1

Determine concentration of a substance in an unknown sample by comparing it to a set of standard samples of known concentrations

Question 2

Suggest why it is important all samples are from the same plant tissue

Answer 2

• standardise test

- different plant tissues could have different water potentials

Question 3

Suggest why a potato chip cutter is used to cut samples

Answer 3

Provide constant cross sectional area

Question 4

Suggest why sucrose solution is used to determine water potential of plant tissue

Answer 4

• sucrose molecules too large to pass through cell-surface membrane
• so any change in mass of samples is due to osmosis

Question 5

Suggest why bungs are placed on top of sucrose solutions with samples

Answer 5

• prevent evaporation of sucrose solution

- water potential of solution does NOT change

Question 6

Suggest why thin samples of potato are cut

Answer 6

• large surface area to volume ratio

- more water taken up per unit time

Question 7

Suggest why skin of potato is removed

Answer 7

• skin prevents passage of water in and out of cells

- ensures osmosis can occur

Question 8

Suggest why samples are blotted before they are weighed

Answer 8

Remove excess water which could alter the weight

Question 9

Suggest why it is important not to squeeze samples when drying

Answer 9

So that water is not removed that entered by osmosis

Question 10

Suggest how to determine water potential of plant tissue

Answer 10

• plot calibration curve (mention what is in each axis)
• interpolate concentration when ratio one / percentage change in mass zero
• use another resource to convert concentration of solution to water potential