What processes allows cells to concentrate material that is present only in very small amounts in the extracellular fluid?

receptor-mediated endocytosis

Explanation:

A selective mechanism that is responsible for endocytosis and transcytosis of the small amounts of materials that are present in the extracellular fluid is known as receptor-mediated endocytosis. The various molecules that can be taken up by this process include hormones, metabolites, proteins as well as certain viruses. This process is also known as clathrin-mediated endocytosis. In this process, the receptors that are present on the surface of the proteins are captured by a molecule which is the target site for the protein and internalized by membrane internalization (endocytosis). The vesicle formed by endocytosis is a clathrin coated vesicle.