Answer
External regulatory proteins that increase the rate of cell division during an organism's development are called growth factors.
Work Step by Step
Proteins that respond to events outside the cell are called external regulators. External regulators can cause the cell cycle to speed up or slow down. Growth factors are important external regulators. Growth-factor proteins control the cell cycle when you have an injury, such as a broken bone. They are also involved in controlling the cell cycle during the development of an embryo.
