Final answer:
Cadherins require calcium ions to function, whereas integrins, which also play a role in cell adhesion, do not require calcium for their binding activity.
Step-by-step explanation:
The question concerns cell adhesion molecules and which of them require calcium ions (Ca2+) for their function. Out of the listed options, namely immunoglobulin superfamily (IgSF) proteins, integrins, selectins, and cadherins, it is the cadherins that require calcium ions to function properly. Cadherins are calcium-dependent adhesion molecules crucial for forming adherens junctions, like desmosomes, which are the 'glue' that binds cells to form cohesive tissues. Integrins, on the other hand, form focal adhesions and link cells to the extracellular matrix but do not require calcium ions for their binding activity.