Cell Biology - Membrane Transport

The plasma membrane follows the Fluid Mosaic Model, consisting of a phospholipid bilayer where phospholipids are amphipathic, containing a hydrophilic phosphate head and two hydrophobic fatty acid tails.

Simple Diffusion is the passive movement of small, non-polar molecules like $O_2$ and $CO_2$ from a region of high concentration to low concentration until equilibrium is reached.

Facilitated Diffusion involves the movement of polar molecules or ions (e.g., $C_6H_{12}O_6$, $Cl^-$, or $Na^+$) across the membrane through specific channel or carrier proteins without the use of $ATP$.

Osmosis is the net movement of $H_2O$ molecules across a partially permeable membrane from a region of lower solute concentration (hypotonic) to a region of higher solute concentration (hypertonic).

Active Transport requires energy in the form of $ATP$ to move substances against a $concentration \ gradient$ using protein pumps, such as the Sodium-Potassium pump ($Na^+/K^+$ pump).

The Sodium-Potassium pump specifically moves $3 \ Na^+$ ions out of the cell and $2 \ K^+$ ions into the cell to maintain resting potential in neurons.

Vesicular transport involves the fluidity of the membrane to allow for $endocytosis$ (internalization of substances) and $exocytosis$ (secretion of substances), both of which are active processes.