AP Biology Chapter 5

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Chapter 5 terms and definitions

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 the adjacent plasma membranes do not touch but are held together by intercellular filaments attached to buttonlike thickenings

carrier protein

protein that combines with and transports a molecule or ion across the plasma membrane.

cell recognition protein

glycoprotein that helps the body defend itself against pathogens

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

cholesterol

one of the major lipids found in animal plasma membranes; makes the membrane impermeable to many molecules.

concentration gradient

gradual change in chemical concentration from one point to another.

crenation

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

differentially permeable

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

diffusion

movement of molecules or ions from a region of higher to lower concentration; it requires no energy and tends to lead to an equal distribution

endocytosis

process by which substances are moved into the cell from the environment by phagocytosis (cellular eating) or pinocytosis (cellular drinking); includes receptor mediated endocytosis

enzymatic protein

protein that catalyzes a specific reaction

exocytosis

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

facilitated transport

passive transfer of a substance into or out of a cell along a concentration gradient by a process that requires a carrier.

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 between cells.

glycolipid

lipid in plasma membranes that bears a carbohydrate chain attached to a hydrophobic tail.

glycoprotein

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.

hypotonic 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

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

phagocytosis

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

phospholipid bilayer

...

pinocytosis

process by which vesicle formation brings macromolecules into the cell

plasmodesmata

in plants, cytoplasmic strands that extend through pores in the cell wall and connect the cytoplasm of two adjacent cells.

plasmolysis

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

carrier protein in the plasma membrane that moves sodium ions out of and potassium ions into animal cells; important in nerve and muscle cells

solute

substance that is dissolved in a solvent, forming a solution.

solution

fluid (solvent) that contains a dissolved solid (the solute)

solvent

liquid portion of a solution that serves to dissolve a solute

tight junction

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

tonicity

osmolarity of a solution compared to that of a cell. If the solution is isotonic to the cell, there is no net movement o f water; if the solution is hypotonic the cell gains water; and if the solution is hypertonic, the cell loses water.

turgor pressure

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

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