Final answer:
Ion channels are proteins in the cell membrane that allow ions to move in and out of the cell. They are specific and can be voltage-gated or ligand-gated.
Step-by-step explanation:
Ion channels are proteins in the cell membrane that allow ions to move in and out of the cell. They are very specific, allowing only certain ions through. There are different types of ion channels, including voltage-gated channels that open or close in response to electrical signals, and ligand-gated channels that open or close when a specific molecule binds to them.
Examples of ions that can pass through ion channels include sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl-). These ions play important roles in various cell functions, such as nerve transmission and muscle contraction.