What is the primary function of red blood cells?

The primary function of red blood cells is to carry oxygen to the cells throughout the body. Red blood cells contain hemoglobin, a specialized protein that binds to oxygen in the lungs and transports it to various tissues and organs where it is needed for cellular respiration and energy production. This is essential for maintaining proper function in the body, as oxygen is critical for the survival of all cells.

The other options refer to functions not associated with red blood cells. For instance, regulating blood sugar levels is primarily the role of insulin and other hormones produced by the pancreas, while connective tissues, such as ligaments, connect bones to bones, contrasting with the function of blood cells. Additionally, enzyme production for digestion is primarily carried out by the pancreas and other digestive organs, rather than by red blood cells.