The inner membrane is freely permeable only to oxygen, carbon dioxide, and water. Its structure is highly complex, including all of the complexes of the electron transport system, the ATp synthetase complex, and transport proteins. The wrinkles, or folds, are organized into lamellae ( layers, called the cristae(脊,嵴). The cristae greatly increase the total surface area of the inner membrane. The larger surface area makes room for many more of the above-named structures than if the inner membrane were shaped like the outer membrane.The inner membrane is freely permeable only to oxygen, carbon dioxide, and water. Its structure is highly complex, including all of the complexes of the electron transport system, the ATP synthetase complex, and transport proteins. The wrinkles, or folds, are organized into lamillae (layers), called the cristae (脊，嵴). The cristae greatly increase the total surface area of the inner membrane. The larger surface area makes room for many more of the above-named structures than if the inner membrane were shaped like the outer membrane