Final answer:
Ion channels are typically gated, which means they can open or close in response to specific signals like electrical or chemical stimuli. They are important in the transmission of electrical impulses in nerve and muscle cells and do not operate via active transport.
Step-by-step explanation:
What is typically true of ion channels? The answer to this question is B) They are gated. Ion channels allow charged ions like sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl-) to move through membrane channel proteins. These channels are not open all the time; they are gated, which means they can open or close in response to various stimuli such as electrical or chemical signals.
Gated ion channels can be further subclassified based on their gating mechanisms. For example, ligand-gated channels open in response to the binding of a certain molecule, while voltage-gated channels require a change in electrical voltage across the membrane. Cells that are involved in the transmission of electrical impulses, such as nerve and muscle cells, typically contain these kinds of gated ion channels.
Therefore, option D, which refers to active transport, is not correct as ion channels do not directly use energy to move ions across membranes; they facilitate passive transport where ions move according to their concentration gradient.