The peptide hormone insulin is synthesised in the pancreas and released into the bloodstream. It is then transported to target cells, such as liver and muscle cells, where it stimulates the uptake and storage of glucose.

Which of the following statements explains how insulin is able to act on target cells throughout the body?

1. Insulin is synthesised by the alpha cells of the pancreas.
2. Insulin is soluble in blood plasma because it is a polar molecule.
3. Insulin is complementary to specific cell surface receptors on target cells.