Which substance is able to pass through the outer membrane of mitochondria easily?

The substance that easily passes through the outer membrane of mitochondria is oxygen. The outer membrane of mitochondria is composed of a lipid bilayer that is characterized by its relative permeability. This structure allows small nonpolar molecules like oxygen to diffuse through it without requiring energy or special transport mechanisms.

Oxygen is a small, uncharged molecule, which allows it to move freely across lipid membranes, including both the outer mitochondrial membrane and cellular membranes. This permeability is crucial because oxygen is essential for cellular respiration, the process by which cells produce energy in the form of ATP.

In contrast, substances like amino acids and water are either polar or larger molecules. These would require specific transport mechanisms, such as protein channels or carriers, to facilitate their movement across membranes, making their passage less straightforward compared to that of oxygen. Carbon dioxide, while also a small molecule, is primarily produced in the mitochondria and often exits via different pathways, especially through the inner membrane as part of cellular respiration processes; however, it can pass through the outer membrane but not as efficiently as oxygen.