Cell Transport and Junctions (1.2)

Cell Transport

The process of moving substances across the cell membrane; functions to maintain homeostasis by regulating nutrient intake and waste removal; composed of passive and active mechanisms using the phospholipid bilayer and proteins.

Active Transport

The energy-dependent movement of molecules; functions to move substances against a concentration gradient (low to high); made of specialized transmembrane carrier proteins (pumps) and fueled by ATP.

Endocytosis

The process of bringing bulk material into the cell; functions to ingest large particles or fluids; made of segments of the plasma membrane that fold inward to create a phospholipid vesicle.

Osmosis

The diffusion of water; functions to equalize solute concentrations on both sides of a membrane; composed of water molecules moving through the phospholipid bilayer or specialized protein channels called aquaporins.

Diffusion

The spontaneous movement of particles; functions to distribute substances evenly throughout a space; driven by the kinetic energy of atoms or molecules without the need for structural components.

Exocytosis

The process of exporting bulk material; functions to secrete hormones; neurotransmitters; or waste; made of intracellular phospholipid vesicles that fuse with the plasma membrane.

Vesicle

A small transport container; functions to move and organize substances within the cell; composed of a phospholipid bilayer sac.

Junctions

Points of contact between neighboring cells; function to provide structural support; sealing; or communication; composed of various specialized transmembrane proteins.

Adhering junction

A mechanical linkage; functions to fasten cells into strong; stress-resistant sheets; composed of cadherin proteins anchored to the cytoskeleton (actin or intermediate filaments).

Gap junction

A communication portal; functions to allow the direct passage of ions and small molecules between cells; composed of transmembrane protein assemblies called connexons.

Tight junction

An impermeable seal; functions to prevent the leakage of extracellular fluid between cells; composed of strands of transmembrane proteins (claudins and occludins) that stitch membranes together.