Practical 3

Question 1

What occurs when plant tissue is placed in hypotonic solution?

Answer 1

Water moves into plant tissue by osmosis, plant tissue increases in mass

Question 2

What occurs when plant tissue is placed in hypertonic solution?

Answer 2

Water moves out plant tissue by osmosis, plant tissue decreases in mass

Question 3

What occurs when plant tissue is placed in isotonic solution?

Answer 3

Same water potential inside + outside tissue so mass stays the same

Question 4

What is water potential determined by?

Answer 4

The concentration of solutes
The higher the solute conc, the lower the water potential

Question 5

Dilution series calculation

Answer 5

C1 X V1 = C2 X V2
C1= Conc of stock solution
V1= Volume of stock solution used to make new concs
C2= Conc of solution you’re making
V2= Volume of new solution you’re making

V2 = V1 + volume of distilled water to dilute with

Question 6

Procedure of investigating osmosis using potato tissue

Answer 6

• Make a simple dilution of 1M sucrose to produce 5 concs
• Control temp by placing all boiling tubes containing sucrose solutions in water bath at 30°C
• Cut a potato into equal sized chips
• Blot potato chips dry with paper towel, measure + record initial masses
• Place each potato chip into its own boiling tube + leave for 20 mins then remove + blot dry
• Reweigh each chip + record final masses
• Calculate change in mass + then calculate the percentage change in mass
• Plot a graph of percentage change in mass + use graph to determine conc of sucrose which has same water potential as potato cells
• Use conversion table to look up the conversion of mol/dm-3 into water potential

Question 7

Controlled variables

Answer 7

• Volume of sucrose solution
• Size of potato chips
• Lengh of time left in solution
• Blot each potato chip dry with paper towel

Question 8

Why is percentage change used rather than actual change in mass?

Answer 8

Percentages allow fair comparisons as it takes into account that the potato chips may not all have the same starting mass