Final answer:
The outer membrane of a mitochondrion is not permeable to all small molecules and small proteins; it is selectively permeable and requires transport proteins for the movement of large molecules.
Step-by-step explanation:
The statement that the outer membrane of a mitochondrion is permeable to all small molecules, including small proteins, is false. The outer membrane of a mitochondrion is selectively permeable, meaning that it allows only certain substances to pass through. This membrane contains porin proteins that form channels for small molecules like ions, nutrients, and water to enter and exit the mitochondrion. Large molecules, such as proteins, require specific transport proteins to aid their movement across the outer membrane.