Passive and Active Transport Unit 2 AP Bio

passive transport

the movement of substances across a cell membrane without the use of energy by the cell. Moves with concentration.

Types of passive transport

diffusion, osmosis, facilitated diffusion

diffusion

Movement of molecules from an area of higher concentration to an area of lower concentration. Moves DOWN the gradient. Spontaneous process resulting from the constant motion of molecules. Molecules diffuses DIRECTLY ACROSS MEMBRANE. Different rates of diffusion for different molecules (membrane is still selectively permeable)

selectively permeable

a property of cell membranes that allows some substances to pass through, while others cannot.

Osmosis

Diffusion of water through a selectively permeable membrane. Maintains water balance which is key for survival.

facilitated diffusion

Diffusion of molecules through the membrane via TRANSPORT PROTEINS.

active transport

Transport of a molecule that requires energy
because it moves a solute against its
concentration gradient

types of active transport

endocytosis and exocytosis, cotransport, and pumps

ATP

adenosine triphosphate. Energy source used by cellsUsed in active transport. ATP can transfer the terminal phosphate group to the transport protein, which changes the shape of the transport protein to better move a substance

Pumps

maintain membrane potential

membrane potential

unequal concentrations of ions across the membrane, resulting in an electrical charge

cotransport

the coupling of a favorable movement
of one substance with an unfavorable movement of
another substance

Favorable movement

downhill diffusion

unfavorable movement

uphill diffusion

Exocytosis

the secretion of molecules via vesicles
that fuse to the plasma membrane

Endocytosis

the uptake of molecules from vesicles
fused from the plasma membrane (think: opposite of
exocytosis)

Phagocytosis

when a cell engulfs particles to be
later digested by lysosomes

Pinocytosis

nonspecific uptake of extracellular fluid
containing dissolved molecules

receptor-mediated endocytosis

specific uptake of molecules via solute binding to receptors on the plasma membrane. Allows the cell to take up large quantities of a specific substance