Required Practical 3

Question 1

each potato core should be put in a sucrose solution for approximately 24 hours

why

Answer 1

• to obtain large change in density / conc
• so equilibrium reached

Question 2

you covered potato cores with a moist paper towel until they were needed

why

Answer 2

• prevent evaporation
• loss of water from cells would change initial WP

Question 3

explain why an increase in density would occur

Answer 3

• WP lower in potato
• water enters potato by osmosis
• loss of water from surrounding solution increases density

Question 4

you used changes in density to find the water potential of the potato tissue

give limitations of this method that could make your results / conc unreliable

Answer 4

• temp not constant
• variation in WP of cells
• dye gradually dispenses in sol
• drops of different sizes move at diff speeds
• drop moves too quickly to measure distance / time accurately

Question 5

in this investigation, you were given potato cylinders taken from potatoes of the same variety

give one reason why this was important

Answer 5

have same WP

Question 6

potato skin had been removed from the cylinders given to you

suggest why the potato skin could have affected osmosis

Answer 6

• skin impermeable to water
• skin is different tissue
• CELLS of skin have diff WP

Question 7

in this investigation, you should have used potato cylinders that were all the same length

why

Answer 7

• same surface area
• which affects rate of uptake of water

Question 8

describe how you would use your results for 100% blackcurrant squash to find the rate of osmosis

Answer 8

• find difference in mass
• divide by time

Question 9

explain why the percentage change in mass of potato cylinders would be the dame between 2 sol

Answer 9

no further loss of water