10 Cell Transport

selectively permeable

membrane characteristic that allows some substances through, but not others

passive transport

method of transporting material through a membrane that does not require energy

concentration gradient

occurs when a molecule is more concentrated in one area than another

amphiphilic

molecule or structure possessing a polar or charged area and a nonpolar or uncharged area, making it capable of interacting with both hydrophilic and hydrophobic environments

simple diffusion

diffusion that occurs without the aid of a membrane protein

diffusion

the net movement of a substance from a region of higher concentration to a region of lower concentration

facilitated diffusion

process by which material moves down a concentration gradient (from high to low concentration) using integral membrane proteins

channel protein

membrane protein that allows a substance to pass through its hollow core across the plasma membrane

aquaporin

channel protein that allows water through the membrane at a very high rate

carrier protein

membrane protein that moves a substance across the plasma membrane by changing its own shape

osmosis

transport of water through a semipermeable membrane according to the water's concentration gradient across the membrane that results from the presence of solute that cannot pass through the membrane

solute

a substance dissolved in another substance

solvent

substance capable of dissolving another substance

tonicity

amount of solute in a solution

osmolarity

total amount of solutes dissolved in a specific amount of solution

hypotonic

situation in which extracellular fluid has a lower osmolarity than the fluid inside the cell, resulting in water moving into the cell

hypertonic

situation in which extracellular fluid has a higher osmolarity than the fluid inside the cell, resulting in water moving out of the cell

isotonic

situation in which the extracellular fluid has the same osmolarity as the fluid inside the cell, resulting in no net water movement into or out of the cell

active transport

method of transporting material that requires energy

pump

active transport mechanism that works against electrochemical gradients

primary active transport

active transport that moves ions or small molecules across a membrane and may create a difference in charge across that membrane

secondary active transport

movement of material that results from primary active transport to the electrochemical gradient

uniporter

transporter that carries one specific ion or molecule

symporter

transporter that carries two different ions or small molecules, both in the same direction

antiporter

transporter that carries two ions or small molecules in different directions

endocytosis

type of active transport that moves substances, including fluids and particles, into a cell

lysosome

organelle in an animal cell that functions as the cell's digestive component; it breaks down proteins, polysaccharides, lipids, nucleic acids, and even worn-out organelles

exocytosis

process of passing bulk material out of a cell

vesicle

a membrane-bound structure within a cell in which substances are transported or stored

bulk transport

a means of moving large particles or large quantities of small particles across a membrane by means of a vesicle; requires energy