Final answer:
The ease with which a molecule can pass through the membrane depends on its interaction with the lipid bilayer, the presence of transport proteins, and the existence of a concentration gradient.
Step-by-step explanation:
The ease with which a molecule can pass through the membrane depends on several factors. First, the molecule must be able to interact with the hydrophobic interior of the lipid bilayer. Small, nonpolar molecules like gases (oxygen and carbon dioxide) and lipids can slip easily through the cell membrane. However, polar molecules like glucose, amino acids, and ions cannot pass through the membrane on their own.
Second, the molecule's ability to pass through the membrane is also influenced by the presence of specific transport proteins. These proteins create channels or carriers that facilitate the movement of specific molecules across the membrane. For example, glucose transporters assist in the passage of glucose into cells.
Finally, the existence of a concentration gradient plays a crucial role. Passive transport occurs when a molecule moves from an area of higher concentration to an area of lower concentration. The presence of a concentration gradient allows molecules to diffuse through the membrane more easily.