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passive transport

movement across the cell membrane that does not require energy from the cell

concentration gradient

Difference in concentration of a substance


condition in which the concentration of a substance is equal throughout a space


movement of a substance from an are of high concentration to an are of lower concentration caused by the random motion of particles


diffusion of water through a selectively permeable membrane

hypertonic solution

solution that causes a cell to shrink because of osmosis

hypotonic solution

solution that causes a cell to swell because of osmosis

isotonic solution

solution that produces no change in cell volume because of osmosis

ion channel

doughnut-shaped transport protein with a polar pore through which ions can pass

carrier proteins

transport protein that binds to a specific substance on one side of the cell membrane, carry the substance across the cell membrane, and release it on the other side

Facilitated Diffusion

passive transport because it moves substances down their concentration gradient without using the cell's energy

active transport

the transport of a substance across the cel membrane against its concentration gradient

sodium potassium pump

transports three sodium ions out of a cell and two potassium ions into the cell


movement of a substance into a cell by a vesicle


movement of a substance by a vesicle to the outside of a cell

Receptor Protein

protein that binds to a specific signal molecule enabling the cell to respond to the signal molecule

second messengers

acts as a signal molecule in the cytoplasm

What needs to happen between cells during communication

signal molecules that bind to receptor proteins on cells

When a signal molecule binds to a receptor protein, how does the cell change?

-enables specific ions to cross the cell membrane
-causing the formation of a second messenger
-speeding up chemical reactions inside the cell

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