Transportation Processes Summary

Substances move from high to low concentration areas (concentration gradient) until uniform distribution is achieved.
Occurs in air, liquid, and solids; in the body, it mainly concerns dissolved solutes in fluids.
Plasma membrane is selectively permeable, allowing some molecules to pass through.
- Simple diffusion: Molecules diffuse across the lipid portion of the membrane.
- Facilitated diffusion: Molecules diffuse through the membrane via carriers or channels.
Simple diffusion occurs when small, lipid-soluble, non-charged particles move through the plasma membrane (e.g., gases like oxygen and carbon dioxide, steroid hormones).

Substances move across the plasma membrane via carrier proteins or water-filled protein channels.
Carrier proteins accept only one type of substance, changing shape to move it in/out of the cell.
Protein channels move ions/water through the channel based on the concentration gradient; can be always open (leakage channels) or gated.

Passive transport of water across a membrane from low to high solute concentration to equalize water content.
Stops when osmotic pressure between fluid compartments equalizes.

Isotonic solution: No net water movement.
Hypotonic solution: Lower solute concentration, net water movement into the cell.
Hypertonic solution: Higher solute concentration, net water movement out of the cell.

Requires energy (ATP) to move substances against their concentration gradient (low to high).
Example: Sodium-potassium pump: Moves sodium out and potassium into the cell.
ATP (Adenosine Tri Phosphate) provides the energy.
Ion pumps: Proteins transport ions across the cell membrane using energy.
Sodium-potassium exchange pump: Maintains higher extracellular $[Na^{+}]$ and higher intracellular $[K^{+}]$ .