By what process does a section of the plasma membrane of a cell bulge inward to form a pocket around extracellular fluid or molecules that eventually pinches off to become a vesicle contained within the cell

The correct answer is endocytosis.

Endocytosis is an active process in which a cell transports molecules into the cell by engulfing them. Different particles can be engulfed such as large molecules, parts of cells, and even whole cells. Endocytosis can be divided into a few steps:

1. invagination of the plasma membrane,

2. formation of a pocket around the target particle,

3. pinching off the pocket,

4. formation of the intracellular vesicle formed from the plasma membrane.