Somatotropin is a hormone that plays a crucial role in growth and development. It stimulates the growth of bones, muscles, and other tissues in the body. Additionally, somatotropin also promotes protein synthesis, which is the process by which cells build proteins. This is important for the growth and repair of tissues, as proteins are essential building blocks for cells. Therefore, the correct answer, "growth" and "increase protein synthesis," accurately describe the effects of somatotropin on the body.