Major Concepts to Review for AP Biology

Cell Transport ( Membrane Funtions)


Plasma membrane's

lipid bilayer phospholipids + Cholesterol to adjust fluidity

various proteins - transmembraneal, Integral, periferal, surface

Fluid mosic Model

Directional with distince inside and outside with may not be switched

Turnover is constant new membrane added (exocytosis) and old removed (endocytosis)


Depends on type of proteins

General functions: Barrier, import and export of materials, homeostasis, maintenance of chemical gradients (including action potential), detection of stimuli (like hormones, light etc.)


Special junctions designed for communication between adjacent cells


Gap Junctions - animals

Plasmodesmata - plants


Mechanisms of Transport
Passive Transport

Diffusion (heat)

Osmosis, water potential, hydrostatic or turgor pressure

Facilitated Diffusion - Permeases

Active transport
pumps may be cotransport or uniport

Special pumps include

Na+ / K+ (especially in nerve cells)

H+ (mitochondria and chloroplasts relie on proton pumps)

Ca+2 (controls muscle contractions)

Endocytosis / Exocytosis (involves large membrane patches or domains)

Receptor mediated (clathrin and caveolae)

Additional Information may be found at: