Osmosis GCSE

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Osmosis

The diffusion of water molecules, from a region where they are in higher concentration, to a region where they are in lower concentration, through a semi-permeable membrane.

Dilute solution

Has a high water potential

Concentrated solution

Has a low water potential

Semi - permeable membrane

A membrane that allows the free diffusion of some small solute molecules but not others

Diffusion

Movement of molecules from an area of higher concentration to an area of lower concentration.

Concentration gradient

A difference in the concentration of a substance across a distance.

Turgid cell

Cell placed in dilute solution and absorbs an excessive amount of water

Plasmolysed cell

Excessive loss of water through osmosis

What drives osmosis?

Difference in water potential across a partially permeable membrane.

Hypotonic solution?

Solution with higher water potential (lower solute concentration) than the cell, causing water to enter the cell.

Hypertonic solution?

Solution with lower water potential (higher solute concentration) than the cell, causing water to leave the cell.

Isotonic solution?

Solution with the same water potential as the cell, causing no net water movement.

Animal cell in hypotonic solution?

Swells and may burst (lysis - a puncture) due to water entering the cell.

Plant cell in hypotonic solution?

Becomes turgid as the cell wall prevents bursting.

Animal cell in hypertonic solution?

Shrinks (crenates) as water leaves the cell.

What happens to a plant cell in hypertonic solution?

Becomes plasmolysed as the cytoplasm and membrane pull away from the cell wall.

How does osmosis keep cell structure?

Maintains turgor pressure (water pressing against the cell walls), keeping plants upright and firm.

Importance of osmosis for life?

Regulates water balance, maintains cell turgidity, aids in root water absorption, and supports kidney function in animals.