Filtration, diffusion, and osmosis are all processes that involve the movement of substances, but they differ fundamentally in their driving forces and selectivity.
Key Differences Summarized
| Feature | Filtration | Diffusion | Osmosis |
|---|---|---|---|
| Driving Force | Pressure gradient | Concentration gradient | Concentration gradient of water |
| Selectivity | Size-based, non-selective | Depends on molecule properties | Water moves selectively |
| Movement | Solutes and solvent | Solutes (typically) | Solvent (water) |
In-Depth Comparison
Filtration
Filtration is a process where fluids and small solutes are forced through a selectively permeable membrane from an area of high pressure to an area of low pressure. The membrane acts as a filter, separating components based primarily on their size.
- Driving Force: Pressure (hydrostatic pressure).
- Selectivity: Primarily based on size. Small molecules and fluids pass through, while larger particles are retained.
- Example: Kidney filtration, where blood pressure forces water and small solutes from the blood into the kidney tubules.
- Specificity: Non-specific; any molecule small enough to pass through the filter will do so.
Diffusion
Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. This movement occurs down the concentration gradient until equilibrium is reached.
- Driving Force: Concentration gradient.
- Selectivity: Depends on the molecule's properties (e.g., size, polarity, charge) and the permeability of any barrier present.
- Example: The movement of oxygen from the lungs into the blood, or the dispersal of a drop of dye in water.
- Specificity: Relatively specific, as different molecules will diffuse at different rates based on their properties and the medium they are diffusing through.
Osmosis
Osmosis is a special type of diffusion specifically referring to the movement of water across a semi-permeable membrane from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration).
- Driving Force: Concentration gradient of water (or water potential).
- Selectivity: Highly selective; only water molecules can pass through the semi-permeable membrane. The membrane is impermeable to at least some solutes.
- Example: The movement of water into plant cells to maintain turgor pressure, or the swelling of red blood cells when placed in a hypotonic solution.
- Specificity: Very specific to water; other molecules cannot pass through the membrane unless specific channels or transport proteins are present.
Key Differences Summarized Again
In essence:
- Filtration uses pressure to force fluids and small molecules across a membrane, separating them based on size.
- Diffusion uses a concentration gradient to move molecules from high to low concentration.
- Osmosis is a specific type of diffusion focusing on the movement of water across a semi-permeable membrane down its concentration gradient.
