What is a primary function of embryonic stem cells?

Embryonic stem cells have a primary function in the capacity to differentiate into various cell types, which allows them to potentially replace faulty or damaged cells in sick individuals. This characteristic is crucial in regenerative medicine and therapeutic applications, as these cells can develop into any type of tissue needed for treatment, such as nerve cells, muscle cells, or pancreatic cells that produce insulin. This ability to transform into specialized cells underscores their significance in addressing a variety of diseases and injuries.

The other options mention functions that stem cells do not possess. For example, while cells do require energy, the production of energy is a role typically associated with mitochondria and not a specific function of embryonic stem cells. Similarly, the transportation of nutrients falls under the role of blood cells and the circulatory system, and fighting infections is primarily carried out by the immune system and its components, not by stem cells. Thus, the unique regenerative capability of embryonic stem cells to replace defective cells is the reason option B is the correct choice.