Which type of endocytosis is characterized by the ingestion of extracellular fluid and its dissolved solutes?

The process characterized by the ingestion of extracellular fluid and its dissolved solutes is pinocytosis. This type of endocytosis is often referred to as "cell drinking" because it involves the uptake of fluid and small particles from the surrounding environment. In this process, the cell membrane invaginates, forming small vesicles that encapsulate the fluid and solutes, which are then brought into the cell.

Pinocytosis is important for nutrient uptake, as it allows cells to sample and absorb the fluid and solutes present in their environment. It is generally a non-specific process, meaning that it does not select specific molecules for uptake, but instead engulfs whatever extracellular fluid is available.

In contrast, phagocytosis involves the ingestion of large particles or even whole cells; receptor-mediated endocytosis is a more specific process where cells take in specific molecules after they bind to receptors on the cell surface; and a catabolic pathway refers to a series of metabolic processes that break down molecules to release energy and does not pertain to the uptake of extracellular fluid. Therefore, pinocytosis is correctly identified as the type of endocytosis that ingests extracellular fluid and dissolved solutes.