RP 3 - Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue Flashcards
Why is it important that the potato cylinders are taken from potatoes of the same variety?
no genetic differences / ensure cells have similar water potential
Potato skin had been removed from the cylinders. Suggest one reason why the potato skin could have affected osmosis
Skin is a different tissue / Potato skin is impermeable to water / potato skin has different water potential
Suggest and explain one reason why it is important to use potato cylinders with the same length.
Similar surface area
Does affect rate of osmosis
Describe how you would use your results for 100% blackcurrant squash to find the rate of osmosis (2)
change in mass
divided by time
Describe how you would use the students results (concentration of sucrose solution and percentage change in mass of potato tissue) to find the water potential of the potato tissue. (3)
Plot a calibration curve of concentration on x-axis and percentage change on y-axis.
Find the concentration where the percentage change is 0.
Find where curve crosses x-axis at 0% change
What occurs when plant tissue is placed in a HYPOTONIC solution?
Water moves INTO the plant by osmosis. plant tissue increases in mass.
What occurs when plant tissue is place in a HYPERTONIC solution?
Water moves OUT of the plant tissue by osmosis, plant tissue decreases in mass.
Why are the potato discs left in solution for 20 mins?
To allow time for osmosis, until the plant tissue reaches equilibrium with the sucrose solution
Why is the percentage change used rather than actual change in mass?
Potato chips may not all have same starting mass
Percentage change allows comparison
Why are the potato chips dabbed dry after removing from the sucrose solution?
To remove any excess water clinging to its surface
What are the controlled variables of this practical?
Volume of sucrose solution
SIze of potato chips
Length of time left in solution
Dab each potato disc with paper towels
