Practical 3 Flashcards
What occurs when plant tissue is placed in hypotonic solution?
Water moves into plant tissue by osmosis, plant tissue increases in mass
What occurs when plant tissue is placed in hypertonic solution?
Water moves out plant tissue by osmosis, plant tissue decreases in mass
What occurs when plant tissue is placed in isotonic solution?
Same water potential inside + outside tissue so mass stays the same
What is water potential determined by?
The concentration of solutes
The higher the solute conc, the lower the water potential
Dilution series calculation
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
Procedure of investigating osmosis using potato tissue
- 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
Controlled variables
- Volume of sucrose solution
- Size of potato chips
- Lengh of time left in solution
- Blot each potato chip dry with paper towel
Why is percentage change used rather than actual change in mass?
Percentages allow fair comparisons as it takes into account that the potato chips may not all have the same starting mass
