AP Biology Cell transport

phospholipid

the main component of the cell membrane that includes a polar (hydrophilic) head and nonpolar (hydrophobic) tail

hydrophilic

attracted to water (like a phospholipid's polar head)

hydrophobic

fearing water (as a phosopholipid's fatty acid tail)

concentration gradient

a gradual difference in solute concentration between the interior and exterior of a cell

passive transport

The movement of molecules across a cell membrane from high to low concentration without the need for energy input

facilitated transport

The movement of molecules across a cell membrane from high to low concentration with the help of a carrier or transport protein; does not require energy

active transport

the movement of molecules across a cell membrane from a region of lower concentration to a region of higher concentration against a concentration gradient

vesicle

A membrane-bound sac in eukaryotic cells that stores or transports the products of metabolism in the cell and is sometimes the site for the breaking down of metabolic wastes

exocytosis

a type of active transport in which vesicles fuse with the cell membrane of a cell to release materials OUT of a cell

endocytosis

a type of active transport in which the membrane buds inward to bring substances into a cell

diffusion

the movement of molecules from an area of high to low concentration until equilibrium has been reached

Brownian motion

The random motion of particles suspended in a fluid resulting from their collision with the fast-moving atoms in the fluid

equilibrium

a condition where there is an equal amount of molecules throughout the entire space

osmosis

the movement of water molecules through a cell membrane barrier from an area of high to low concentration; a form of passive transport

Solute

A substance that is dissolved in another substance, forming a solution

Solvent

The liquid in which a solute is dissolved to form a solution.

hypotonic solution

Less solute concentration and high water concentration

hypertonic solution

High solute concentration and lower water concentration

isotonic solution

a solution that has an equal amount of "free" water molecules inside and outside of the cell or a solution in which the solute concentration is equal inside and outside the cell; water moves in and out of the cell equally

water potential

The physical property predicting the direction in which water will flow, governed by solute concentration and applied pressure.

pressure potential

A component of water potential that consists of the physical pressure on a solution, which can be positive, zero, or negative.

solute potential

A component of water potential that is proportional to the number of dissolved solute molecules in a solution and measures the effect of solutes on the direction of water movement; also called osmotic potential, it can be either zero or negative.

integral proteins

penetrate the hydrophobic interior of the lipid bilayer

peripheral proteins

The proteins of a membrane that are not embedded in the lipid bilayer; they are appendages loosely bound to the surface of the membrane.

gated channels

A protein channel in a cell membrane that opens or closes in response to a particular stimulus.

Osmolarity

total concentration of all solute particles in a solution

Osmoregulation

regulation of solute concentrations and water balance by a cell or organism

contractile vacuole

saclike organelles that expand to collect excess water and contract to squeeze the water out of the cell

Osmoconformers

marine animals which, in contrast to osmoregulators, maintain the osmolarity of their body fluids such that it is always equal to the surrounding seawater.

Osmoregulators

organisms that maintain their internal water balance and solute concentration within narrow limits

Plasmolysis

Collapse of a walled cell's cytoplasm due to a lack of water

turgid

swollen as from a fluid; bloated

lyse

the bursting of a cell

flaccid

limp, not firm

hyperosmotic

solution with a greater concentration of solute

hypoosmotic

organisms with body fluids with a higher concentration of water and lower solute concentration than the external environment.