The mitochondria has two layers - an outer membrane and an inner membrane. The inner membrane folds inward forming cristae which increases the surface area. The cristae has enzymes that are dissolved into the fluid in the mitochondria, called the matrix. The matrix is responsible for releasing energy from glucose through a process called cellular respiration. Since there is so much ATP in the mitochondria, it is known as the "powerhouse." Like a cell membrane protects a cell, that is what the outer membrane of the mitochondria does. It also allows small and big proteins in through the outer membrane. Both work together in order to function. I hope I helped!! If you need more help, then do not hesitate to message me and I will help you the best I can. Have a great day!!