1. Diffusion:
* Definition: The movement of particles from an area of high concentration to an area of low concentration. This occurs naturally due to the random motion of particles.
* Driving Force: The concentration gradient (difference in concentration between two areas).
* Mechanism: No membrane or protein assistance is required. Particles move directly through the membrane or space.
* Example: A drop of food coloring spreading through a glass of water.
2. Facilitated Diffusion:
* Definition: The movement of particles across a membrane with the help of transport proteins.
* Driving Force: Still the concentration gradient.
* Mechanism: Transport proteins provide a pathway or "channel" through the membrane for the particles to move. This can be specific for certain molecules.
* Example: Glucose entering a cell with the help of a glucose transporter protein.
3. Osmosis:
* Definition: The movement of water molecules across a semipermeable membrane from an area of high water concentration to an area of low water concentration.
* Driving Force: The difference in water potential (a measure of the potential of water to move). This is influenced by solute concentration: higher solute concentration means lower water potential.
* Mechanism: Water moves through the membrane, usually via specialized aquaporin channels.
* Example: Water moving into a plant cell from its surroundings, causing it to become turgid (firm).
Key Differences:
* Mechanism: Diffusion is passive and requires no assistance. Facilitated diffusion requires the help of transport proteins. Osmosis is driven by water potential and often uses aquaporins.
* Specificity: Diffusion is non-specific (any particle can move). Facilitated diffusion is specific (only certain particles can move with the help of the appropriate protein). Osmosis is specific for water molecules.
* Energy Requirement: All three processes are passive, meaning they don't require energy input from the cell.
In Summary:
* Diffusion: Simple movement down a concentration gradient.
* Facilitated Diffusion: Diffusion with help from transport proteins.
* Osmosis: Diffusion of water across a semipermeable membrane driven by water potential differences.
Let me know if you have any other questions!
