Practical: Investigating Diffusion & Osmosis

Diffusion

Net movement of particles from high concentration to low concentration

Osmosis

Movement of water through a partially permeable membrane from high to low water potential

Partially permeable membrane

Allows some molecules (like water) to pass through but not others

Surface area

Total area available for diffusion

Concentration gradient

Difference in concentration between two areas

Potato cylinders

Common tissue used to investigate osmosis

Hypotonic solution

Higher water potential than the cell

Hypertonic solution

Lower water potential than the cell

Isotonic solution

Same water potential as the cell

Mass change

Measurement used to determine osmosis in potato experiments

Dialysis tubing

Artificial partially permeable membrane used to model diffusion/osmosis

What is the independent variable in a potato osmosis experiment?

Concentration of the solution

What is the dependent variable in a potato osmosis experiment?

Change in mass or length

Why are potato cylinders dried before weighing?

To remove excess surface water for accurate results

What happens to a potato in a hypotonic solution?

It gains mass (water enters)

What happens to a potato in a hypertonic solution?

It loses mass (water leaves)

What happens to a potato in an isotonic solution?

No net mass change

Why must the same volume of solution be used for each potato?

To keep the test fair (control variable)

Why must potato cylinders be the same size?

To ensure equal surface area for osmosis

Why is percentage change in mass used?

Allows comparison between different‑sized samples

What does a positive percentage mass change indicate?

Water entered the potato (hypotonic)

What does a negative percentage mass change indicate?

Water left the potato (hypertonic)

What is the purpose of dialysis tubing in diffusion experiments?

To model a partially permeable membrane

What diffuses through dialysis tubing in typical experiments?

Small molecules like glucose or iodine

Why does starch not pass through dialysis tubing?

Molecules are too large

What colour change shows iodine diffusing into starch solution?

Yellow‑brown → blue‑black

Why is temperature kept constant in diffusion/osmosis experiments?

Temperature affects particle kinetic energy