What is the process called when cells absorb molecules that cannot otherwise pass through the plasma membrane?

The correct answer is endocytosis, which is the process where cells take in molecules that cannot directly pass through the plasma membrane. This process is essential for cells to obtain larger molecules, nutrients, and other substances that are critical for their functions.

During endocytosis, the cell membrane forms a pocket around the molecules, which then pinches off to form a vesicle inside the cell. This mechanism allows the cell to selectively absorb substances, contributing to its ability to maintain homeostasis and respond to its environment.

In contrast, exocytosis is the reverse process where substances are expelled from the cell. Phagocytosis is a specific type of endocytosis where cells engulf large particles or even other cells. Diffusion is a passive process where molecules spread from areas of high concentration to low concentration but does not involve vesicular transport or the absorption of larger molecules. Thus, the specific nature of endocytosis makes it the correct answer for the described process.