Final answer:
Receptor-mediated endocytosis is a highly selective form of active transport where cells engulf extracellular molecules bound to receptor proteins, leading to the formation of clathrin-coated vesicles. The correct answer to the student's question is (d) Receptor-mediated endocytosis.
Step-by-step explanation:
When a cell membrane engulfs selected molecules that have combined with receptor proteins on its surface, the process is called receptor-mediated endocytosis. This is a highly selective and targeted form of endocytosis that involves specific receptor proteins in the plasma membrane.
These receptors have a strong binding affinity for certain substances. Upon the binding of their respective ligands, these receptor proteins aggregate in specialized regions of the cell membrane known as coated pits. Subsequently, these coated pits invaginate and pinch off to form clathrin-coated vesicles, bringing the extracellular substances into the cell.
In contrast to other forms of endocytosis such as phagocytosis and pinocytosis, receptor-mediated endocytosis is efficient in how it selectively takes in large molecules or complexes that a cell requires.
After the internalization of these substances, the vesicle membranes are often recycled back to the plasma membrane, ready to be reused. Given these characteristics, the correct option for the student's question is (d) Receptor-mediated endocytosis.