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active transport

use of a plasma membrane carrier protein to move a molecule or ion from a region of lower concentration to one of higher concentration; it opposes equilibrium and requires energy.

adhesion junction

junction between cells in which adjacent plasma membranes do not touch but are held together by intercellular filaments attacked to buttonlike thickenings.


channel protein through which water can diffuse across a membrane

bulk transport

movement of elements in an organism in large amount

carrier protein

protein that combines with a molecule or ion to transport it across the plasma membrane

cell recognition protein

glycoprotein that helps the body recognize when it is being invaded by pathogens so that an immune response can occur

cell wall

structure that surrounds a plant, protistan, fungal, or bacterial cell and maintains the cell's shape and rigidity.

channel protein

protein that forms a channel to allow a particular molecule or ion to cross the plasma membrane


a steroid that forms an essential component of animal cell membranes and acts as a precursor molecule for the synthesis of other biologically important steroids.

concentration gradient

difference in the number of molecules or ions of any one substance between two adjoining regions


in animal cell, shriveling of the cell due to water leaving the cell when the environment is hypertonic


intercellular junction that connects cytoskeletons of adjacent cells; fastens cells together as strong sheets

differentially permeable

ability of membranes to regulate the passage of substances into and out of the cell; allowing some to pass through and preventing the passage of others


net movement of like ions or molecules from a region where they are most concentrated to an adjoining region where they are less concentrated; they move down their concentration gradient and use no energy


cell uptake of substances by forming vesicles from patches of plasma membrane. three modes: receptor-mediated endocytosis, phagocytosis, and pinocytosis (cell drinking)

enzymatic protein

protein that catalyzes a specific reaction


process in which an intracellular vesicle fuses with the plasma membrane so that the vesicle's contents are released outside the cell

extracellular matrix

nonliving substance in which animal cells are imbeded; is composed of protein and polysaccharides

facilitated transport

passive transfer of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradients. moves from high to low concentration.

fluid-mosaic model

model for the plasma membrane based on the changing location and pattern of protein molecules in a fluid phospholipid bilayer

gap junction

junction between cells formed by the joining of two adjacent plasma membranes; it lends strength and allows ions, sugars, and small molecules to pass through cells


lipid in plasma membranes covalently bonded to a carbohydrate


protein in plasma membranes that bears a carbohydrate chain

hypertonic solution

higher solute concentration (less water) than the cytoplasm of a cell; causes cell to lose water by osmosis

hyopotonic solution

lower solute (more water) concentration than the cytoplasm of a cell; causes cell to gain water by osmosis

isotonic solution

solution that is equal in solute concentration to that of the cytoplasm of a cell; causes cell to neither lose nor gain water by osmosis


diffusion of water through a differentially permeable membrane

osmotic pressure

measure of the tendency of water to move across a differentially permeable membrane; visible as an increase in liquid on the side of the membrane with higher solute concentration


process by which amoeboid-type cells engulf large substances, forming an intracellular vacuole


process by which vesicle formation brings macromolecules into the cell.


in plants, cytoplasmic strands that extend through pores in the cell wall and connect the cytoplasm of two adjacent cells
substances can travel between cells this way


contraction of the cell contents due to the loss of water

receptor-mediated endocytosis

selective uptake of molecules into a cell by vacuole formation after they bind to specific receptor proteins in the plasma membrane

receptor protein

protein located in the plasma membrane or within the cell; binds to a substance that alters some metabolic aspect of the cell

sodium-potassium pump

cotransporter that, when energized, actively transports sodium out of a cell and helps potassium passively diffuse into it at the same time

tight junction

junction between cells when adjacent plasma membrane proteins join to form an impermeable barrier


the ability of a solution to cause a cell within it to gain or lose water

turgor pressure

pressure of the cell's contents against the cell wall; in plant cells, determined by the water content of the vacuole and provides internal support

junction protein

protein that assists cell-to-cell communication at the plasma membrane

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