Cells: Investigating Water Potential Practical

Question 1

What is the aim of this experiment?

Answer 1

• To use potato cylinders and sucrose solutions to find out the water potential of plant tissue

Question 2

What is a serial dilution?

Answer 2

• A serial dilution is when you create a set of solutions that decrease in concentration by the same factor each time

Question 3

How do you make serial dilutions?

Answer 3

• Choose an initial sucrose concentration (1M) and a factor that you will dilute each solution by (0.2)
• Calculate how much sucrose solution and distilled water you need in each test tube using:
• m1v1=m2v2
• m1 = concentration of initial solution
• v1 = volume of initial solution needed
• m2 = desired concentration
• v2 = volume of final solution

Question 4

How do you measure the change in mass in potato cells?

Answer 4

• Use a cork borer to cut potatoes into identically sized chips, about 1cm in diameter
• Measure mass using a mass balance
• Place a potato cylinder in each of your sucrose solutions and leave for at least 20 minutes
• Remove potato cylinders and pat dry with a paper towel
• Weigh each potato cylinder again and record results
• Calculate percentage change in mass for each group

Question 5

Describe which potato cylinders will gain/lose mass and explain why

Answer 5

• Potato cylinders will gain water and therefore mass in hypotonic solutions
• Potato cylinders will lose water and therefore mass in hypertonic solutions

Question 6

How do you produce a calibration curve?

Answer 6

• Produce a calibration curve by plotting concentration of sucrose solution against the percentage change in mass
• The point at which the calibration curve crosses the x-axis (where % change in mass is 0) is the point at which the water potential of the solution is the same as the water potential of the potato cells
• Find concentration of this point then look up the water potential for that concentration of sucrose solution