Cell Biology - Membrane Transport (Diffusion, Osmosis, Active Transport)

Simple Diffusion: The passive net movement of particles from a region of higher concentration to a region of lower concentration ($[high] \rightarrow [low]$) down a concentration gradient. It occurs with small, non-polar molecules like $O_2$ and $CO_2$.

Facilitated Diffusion: The passive movement of specific molecules (like glucose or ions such as $Cl^-$) across a cell membrane via specific transmembrane integral proteins (carrier or channel proteins).

Osmosis: The net movement of water molecules ($H_2O$) from a region of higher water potential (hypotonic solution) to a region of lower water potential (hypertonic solution) through a partially permeable membrane.

Active Transport: The movement of substances against a concentration gradient ($[low] \rightarrow [high]$). This process requires energy in the form of $ATP$ and involves specific protein pumps, such as the $Na^+/K^+$ pump.

Factors Affecting Transport Rate: The rate of exchange is influenced by the concentration gradient ($\Delta C$), temperature ($T$), and the available surface area ($SA$).

Surface Area to Volume Ratio ($SA:V$): As a cell grows, its volume increases at a cubic rate while surface area increases at a squared rate. A high $SA:V$ ratio is essential for efficient diffusion of nutrients and waste products.