Final answer:
MHC class I molecules are found on all nucleated cells and play a crucial role in presenting antigens to the immune system.
Step-by-step explanation:
MHC class I molecules are indeed found on all nucleated cells. They play a crucial role in presenting antigens to the immune system and are involved in cellular immunity. MHC II molecules, on the other hand, are found only on specific immune cells such as macrophages, dendritic cells, and B cells.