RP3 - production of dilution series to produce calibration curve to identify water potential of plant tissues

Question 1

suggest why it is important to take potato cylinders from the same variety

Answer 1

• same/similar water potential
• so no genetic differences

Question 2

potato skin has been removed from cylinders. suggest how potato skin could have affected osmosis

Answer 2

• skin = impermeable to water
• skin is a different tissue
• skin cells = different water potential

Question 3

suggest and explain one reason why is important to use potato cylinders of same length

Answer 3

• same/similar surface area
• otherwise affects rate of osmosis

Question 4

describe how 100% blackcurrant squash can be used to find the rate of osmosis

Answer 4

final mass - initial mass / time

Question 5

explain why percentage change in mass of potato cylinders is the same in solutions B and C

Answer 5

no further water loss

Question 6

what is meant by processed results

Answer 6

calculations made from raw data

Question 7

describe how you would use 1.0 moldm-3 solution to produce 30cm3 of 0.15mol dm-3 of sucrose

Answer 7

4.5cm3 of 1.0 moldm-3 sucrose solution (0.15 x 30)
25.5cm3 of water (to make up 30cm3)

Question 8

explain why there is negative percentage change in potato mass

Answer 8

• lower water potential in solution compared to potato
• potato loses water via osmosis

Question 9

describe how you would use results to find water potential of potato tissue

Answer 9

• plot a graph with concentration on the x-axis and percentage change in mass on the y-axis
• find concentration where % change = 0
• use another resource to find water potential of sucrose concentration (where curve crosses x-axis)

Question 10

students gave results as ratio. what is the advantage of this

Answer 10

allows comparison

Question 11

reliability can be improved by taking several readings at same concentration. explain how

Answer 11

• anomalies identified
• mean can be calculated

Question 12

students used graph of results to find sodium chloride solution with same water potential as apple tissue. describe how

Answer 12

• draw line of best fit
• read off from graph to find concentration where % change in mass is 0

Question 13

describe method used to produce calibration curve. start after potato cubes cut

Answer 13

• place potato cubes in sucrose solution
• control temperature e.g. room temp
• dry cubes before measuring
• measure mass of cubes