Required Practical 3 - Water Potetial

Question 1

What is the purpose of calibration curves

Answer 1

Are used to determine 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 with percentage change in mass against concentration

- find the x-intercept where the plant is isotonic to the sucrose solution

Question 3

What happens when plant tissue is placed in hypotonic solution

Answer 3

• water moves into the plant

- plant tissue increases in mass

Question 4

What happens when plant tissue is placed in a hypertonic solution

Answer 4

• water moves out of the plant tissue

- mass decreases

Question 5

What are the potato disks left in the solution for 20 mins

Answer 5

to allow time for osmosis until the plant reaches equilibrium with surrounding sollution

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

Method

Answer 7

1. prepare a serial dilution of solute from a known concentration
2. prepare cylinders of plant tissue eg potato
3. weigh mass of each cylinder
4. submerge cylinders in the range of solute concentrations for 1hr
5. weigh cylinders again
6. calculate the percentage change in mass
7. plot solute concentration vs percentage change to form a calibration curve
8. use calibration curve to estimate the water potential of plant tissue

Question 8

Why is the percentage change used not actual mass

Answer 8

• potato chips may not have the same starting mass

- percentage change allows comparison

Question 9

Why is there a change in the mass of the potato chips

Answer 9

• the potato chips with a concentration lower than the sucrose solution will lose mass as there is a net movement of water out of cells
• potato chips with a concentration higher than the sucrose solution gain mass as there is a net water movement in the cell

Question 10

Why are the potato chips dabbed dry after removing from the sucrose solution

Answer 10

To remove excess water clinging to its surface

Question 11

What are the controlled variables

Answer 11

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

Question 12

calculation to make serial dilution

Answer 12

total volume/ known concentration x desired concentration

- number for desired concentration will be given in the question