Diffusion and Osmosis - Practical Skills

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 unto osmosis using potato tissue

Answer 2

• Cut identical potato cylinders using a cork borer
• Measure and recored the length and mass of cylinders using ruler and balance
• Add each cylinder to one of 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 graph of change in mass in grams (y axis) against concentration of suction is 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 to changes in length an mass can be compared easily

Question 4

Why is it necessary to block 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 allows 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 solution that is isotonic to the plant cells

Question 7

State the source of error in this practical

Answer 7

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

Question 8

What equipment can be used to investigate osmosis in non-living systems?

Answer 8

Using a capillary tube inserted into a Viking tube, placed in a beaker of solution

Question 9

What indicates osmosis in the non-living system?

Answer 9

The change in water level in the capillary tube

Question 10

What is the change in water level when the Visking tube filled with water is placed in sucrose solution?

Answer 10

Water level drops and water moves out of the visking tube by osmosis

Question 11

What is the change in water level when the visking tube filled with sucrose solution is placed in water?

Answer 11

Water level rises and water moves into the vision tube by osmosis

Question 12

State the observation of placing a potassium permanganate crystal into a beaker of distilled water

Answer 12

Purple colour spreads through solution, and the solution eventually beaches uniformly purple