Osmosis (AQA GCSE Biology)

Flashcards covering key concepts, definitions, and applications of osmosis based on AQA GCSE Biology notes.

What is osmosis?

The movement of water molecules across a partially permeable membrane from a region of higher water concentration (dilute solution) to a region of lower water concentration (more concentrated solution).

Is osmosis an active or passive process?

Passive — it does not require energy.

What type of membrane does osmosis occur across?

A partially permeable membrane (allows water molecules through, but not larger solute molecules).

Why is osmosis important in plant cells?

Keeps cells turgid (firm), which supports the plant. Helps plants stay upright and not wilt.

What happens to an animal cell placed in pure water?

Water enters by osmosis → cell may swell and burst (lysis), as animal cells lack a cell wall.

What happens to an animal cell placed in a concentrated salt/sugar solution?

Water leaves by osmosis → cell shrinks and shrivels.

What happens to a plant cell placed in pure water?

Water enters by osmosis → cell becomes turgid (swollen but does not burst, due to cell wall).

What happens to a plant cell placed in a concentrated solution?

Water leaves by osmosis → cytoplasm and membrane shrink away from the cell wall (plasmolysis).

Which factors affect the rate of osmosis?

Difference in concentration (concentration gradient). Temperature (affects kinetic energy of water molecules). Surface area of the membrane.

How do root hair cells use osmosis?

Water enters root hair cells from the soil by osmosis, allowing plants to absorb water for transport and photosynthesis.

How might osmosis be tested in a school lab experiment?

Using potato cylinders in solutions of different sugar concentrations, measuring mass gain/loss to show water movement by osmosis.

What part of the AQA spec covers osmosis?

Transport in cells → along with diffusion and active transport.