Key Terms
Phospholipids are amphipathic
They have both a hydrophilic region and a hydrophobic region.
Integral proteins
Span the entire bilayer.
Peripheral proteins
Attached to the surface (inner or outer) of the bilayer; do not span it. Often perform specific enzymatic functions.
Glycoproteins
Integral proteins with attached carbohydrates that extend into the extracellular space.
Simple diffusion
Small, nonpolar molecules cross directly through the lipid bilayer, moving from high concentration to low concentration
Facilitated diffusion
Large, polar, or charged molecules cannot cross the bilayer directly; they use channel or carrier proteins. Still moves
Osmosis
Diffusion of water across a semipermeable membrane. Water moves from areas of low solute concentration (high water conce
Filtration
Hydrostatic pressure pushes fluid (and dissolved solutes) from high pressure to low pressure. Used in capillaries and ki
Secondary active transport
One active pump creates a concentration gradient that then powers transport of a second substance passively.
Endocytosis
Cell engulfs material by wrapping membrane around it; forms a vesicle.
Exocytosis
Vesicle inside the cell fuses with the membrane and releases contents outside. Example: secretion of digestive enzymes b
Endoplasmic Reticulum (ER)
A network of membrane channels continuous with the nuclear envelope.
Golgi Apparatus
The post office of the cell.
Lysosomes
Membrane-bound sacs containing digestive enzymes; produced by the Golgi.
Mitochondria
The energy transformers.