required practical 3

Question 1

what is the aim of this required practical?

Answer 1

to produce a dilution series of a solute to produce a calibration curve which can be used to identify the water potential of plant tissue

Question 2

what is a calibration curve?

Answer 2

a graph used to determine an unknown concentration of a sample, by comparing the unknown to a set of standard samples with known concentrations (standard curves)

Question 3

how do you create a dilution series?

Answer 3

1. work out what volume of 1M sucrose solution is required for that particular concentration
2. work out what volume of distilled water must be added to the sucrose solution to achieve the required volume of the dilution
3. add the sucrose solution and water to the same boiling tube
4. repeat for the other concentrations

Question 4

how do you calculate the volume of stock (sucrose) solution needed for a dilution series?

Answer 4

V1 = C2 x V2/ C1
V1 = volume of stock solution needed
C2 = final concentration (desired concentration for each solution)
V2 = final volume
C1 = concentration of initial solution

Question 5

what is the method for the practical?

Answer 5

1. make a dilution series of 1M sucrose solution - they should be at 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0M sucrose, and diluted using distilled water
2. measure 20cm^3 of each dilution into separate boiling tubes
3. stand the boiling tubes with the sucrose solutions in a water bath at 30 degrees (check using thermometer)
4. use a cork borer to cut six potato chips, and cut them so they are identical in size (remove any skin)
5. use a paper towel to remove excess water from the chips
6. weigh each chip and record the mass and concentration of solution it will be in
7. place one potato chip in each test tube and leave for 20 minutes
8. remove each chip, dry gently and weigh and record the mass of each one
9. calculate the percentage change in mass for each sucrose solution
10. plot a graph of % change in mass against concentration of sucrose solution

Question 6

what is the risk assessment for this practical?

Answer 6

hazard/risk/prevention
scalpel/cuts/cut away from fingers, use forceps to hold sample when cutting, keep away from edge of desk
broken glass/cuts/be careful when handling glass objects, keep glassware away from edge of desk

Question 7

what are important controls for this practical?

Answer 7

variety of potato (different varieties may have different concentrations inside which would affect osmosis)
surface area of potato chip (if they had different surface areas it would affect how much osmosis occurs in each one)
time left in water bath

Question 8

what is the conclusion for this practical?

Answer 8

potato chips in low concentrations of glucose solution will increase in mass - the solution will have a higher water potential than the potato, so water moves via osmosis into the potato where there is a lower water potential
potato chips in high concentrations of glucose solution will decrease in mass - the potato will have a higher water potential than the solution, so water moves via osmosis out of the potato into the solution where there is a lower water potential