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- Movement of solute particles from and area of high concentration to an area of low concentration
- No energy required
- molecules are carried across the membrane by (globular) proteins which collect them on one side of the membrane, diffuse across it and deposit them on the other side of the the membrane.
- eg: glucose
- eg: channel protein - amino acids
The movement of water (solvent) from an area of high water concentration (hypotonic) with low solute concentration to an area of low water concentration (solute) with high solute concentration.
- Transport of molecules across a membrane
- Required energy
- Substance moved against natural tendency
- movement is unidirectional
- may involve: carrier molecules or formation/breakdown of membrane bound packages
- Exocytosis - movement substances OUT of cell
- Endocytosis - movement substances INTO cell
- Phagocytosis - cellular eating
- Pinocytosis - cellular drinking
allows diffusion of both solute and solvent molecules in both directions
excludes diffusion of solute molecules purely on size, but allows passage of solvent molecules in both directions
initially a solute will be more on one side of a permeable membrane, however as the concentration on both sides equal out the number of molecules passing from each direction will equal out.