Which type of ligand is water soluble, and thus unable to enter a cell?

What type of signaling uses the bloodstream to transport ligands to targets?

Which is false regarding cell signaling?

Which type of cell-surface receptor, when bound by a ligand, begins a cycle where GDP is exchanged for GTP, causing the alpha subunit to separate from the beta and gamma subunits, and causing a cellular response?

A cell releases a ligand that binds to receptors on its own surface. Which type of signaling is this?

Beta cells in the pancreas secrete insulin, a hormone, that enters the bloodstream. This is an example of which type of signaling?