Note: Not all cells have the same relative distribution of organelles. Form will follow function. Cells that require a lot of energy for locomotion (such as sperm cells) have high concentrations of mitochondria. Cells involved in secretion (such as pancreatic islet cells and other endocrine tissues) have high concentrations of RER and Golgi apparatuses. Other cells, such as red blood cells, which primarily serve a transport function, have no organelles at all.