Core practical - Osmosis in potato slices

Question 1

What is osmosis

Answer 1

The movement of water molecules from a higher water potential to a lower water potential through a partially permeable membrane

Question 2

Describe how you would carry out an investigation into osmosis using potato tissue

Answer 2

Cut identical potato cylinders using a cork borer
Measure and record the length and mass of cylinders using ruler and balance
Add each cylinder to one of 3 three solutions: 1M sugar solution, 0.5M sugar solution and distilled water
Leave cylinders in tubes overnight
Remove cylinders from tubes and blot them using paper towels
Record length and mass of each cylinder
Draw a graph of change in mass in grams (y axis) against concentration of solution in mol dm*-3 (x axis)

Question 3

Why is it necessary to use a cork borer to cut the cylinders

Answer 3

Results in equal sized samples so changes in length and mass can be compared easily

Question 4

Why is it necessary to blot the cylinders with paper after removing them

Answer 4

Each cylinder may have a different amount of water on its surface, so masses may vary. Blotting cylinders allow masses to be comparable

Question 5

What safety precautions should be taken with this experiment

Answer 5

Handle cork borer and scalpel with care

Question 6

How can the water potential of the plant cells be found

Answer 6

Plot a graph of change in mass against concentration
Find the x-intercept, which is the concentration of the solution that is isotonic to the plant cells

Question 7

State a source of error in this practical

Answer 7

Plant tissue taken from different parts of the plant may have different water potentials