Practical 3

Question 1

what is the purpose of the calibration curve

Answer 1

they are used to detemine the concentration of an unknown sample by comparing it to a set of standard values with known concentrations

Question 2

how is a calibration curve used to find the concentration of plant tissue

Answer 2

plot a calibration curve of percentage change in mass against concentration and find the x intercept where the plant tissue is isotonic to the sucrose solution

Question 3

what occurs when plant tissue is placed in a hypotonic solution

Answer 3

water moves into the plant tissue by osmosis therefore plant increases in mass

Question 4

what occurs when plant tissue is placed in hypertonic solution

Answer 4

water moves out of the plant tissue by osmosis therefore plant decreases in mass

Question 5

why are the potato discs left in solution for 20 minutes

Answer 5

to all time for osmosis until the plant tissue reaches equilibrium with its surrounding solution

Question 6

what is water potential determined by

Answer 6

the concentration of solutes
the higher the solute concentration then the lower the water potential

Question 7

outline the procedure of the investigating osmosis using potato tissue

Answer 7

1. make a simple dilution to produce 5 concentrations and add to different test tubes
2. cut a potato into equal sized chips and weigh
3. place a chip in each test tube and leave for 20 minutes
4. take out and dab the excess water and weigh them again
5. calculate the percentage change

Question 8

why is the percentage change used rather than the actual change in mass

Answer 8

potato chips may not all have same starting mass
percentage change allows comparison

Question 9

what is indicated by the x intercept of the calibration curve

Answer 9

the concentration that is isotonic to the solution tested

Question 10

explain the change in mass in the potato chips

Answer 10

the potato chips with concentration lower than the sucrose solution lose mass as there is a net movement of water out of the cells
vice versa

Question 11

why are the potato chips dabbed after removing from the sucrose solution

Answer 11

to remove any excess water clinging to the surface

Question 12

what are the control variables in this practical

Answer 12

volume of sucrose solution
size of potato chips
length of time left in solution
dab each potato disc with paper towels