Which process is an example of cell signalling?
Passive diffusion of oxygen molecules across the phospholipid bilayer of an alveolar epithelial cell
Binding of insulin to complementary glycoprotein receptors on the cell surface membrane of a liver cell
Active transport of calcium ions (Ca2+\text{Ca}^{2+}Ca2+) into the sarcoplasmic reticulum of a muscle fibre
Facilitated diffusion of water molecules through aquaporins in the cell surface membrane of a collecting duct cell
