Answer:
Cell surface receptors (membrane receptors, transmembrane receptors) are receptors that are embedded in the plasma membrane of cells. They act in cell signaling by receiving (binding to) extracellular molecules. They are specialized integral membrane proteins that allow communication between the cell and the extracellular space.
Explanation:
what are sound waves* but anyways sound waves are sounds that travel through waves.
example: music travels out of a device into our ear.
I believe the answer is 3.
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