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a lipid made of a phosphate head and two fatty acid tails

lipid bilayer

cell membranes composed of two layers of phospholipids, with the tails pointed inwards towards each other, and the heads facing outward

cell surface markers

a membrane protein that identifies the cell type

receptor proteins

a membrane protein that binds to signals outside the cell

transport proteins

transports substances unable to diffuse across a cell membrane

active transport

energy is required to move a substance across a cell membrane

passive transport

no energy is required to transport substances across cell membranes


when randomly moving molecules fill up a space evenly


the amount of a particular substance in a given volume

concentration gradient

a difference in the concentration of a substance across a distance


substances moving down the concentration gradient (from high to low concentration)

simple diffusion

small, nonpolar molecules passing directly through the lipid bilayer

facilitated diffusion

transport proteins helping ions and polar molecules to diffuse through the bilayer

channel proteins (pores)

tunnels that open for ions and polar molecules to pass through the cell membrane

carrier proteins

a protein that transports substances across a cell membrane by changing shape


the process of water diffusing across a selectively permeable membrane

water channels

channel proteins that aid in osmosis, and only allow water molecules to pass through

hypertonic solution

the solute has high concentration, the water has low, water moves out of the cell

hypotonic solution

the solute has low concentration, the water has high, water moves into the cell

isotonic solution

the solute and water have an equal concentration to the cell's cytoplasm, water moves into and out of the cell at equal rates

contractile vacuoles

colllect excess water in unicellular eukaryotes and force the water out of the cell

sodium-potassium pump

a carrier protein that uses ATP to actively transport 3 sodium ions out of a cell, and 2 potassium ions into a cell


the process of a large substance moving into a cell using a vesicle


the process of a large substance moving out of a cell by means of a vesicle


anything that serves to direct, guide or warn

target cell

a cell that responds to a signal sent by a signaling cell

receptor proteins

a protein that binds to specific signal molecules, causing the cell to respond

permeability change

transport proteins opening or closing in response to a signal


A term used to describe plant tissue where the cells have lost turgor and are not firm.


The pressure that water molecules exert against the cell wall




swollen as from a fluid; bloated


Another term that describes the concentration of solution

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