Which of the following processes involves endocytosis?

• A. Absorption of glucose
• B. Sodium-potassium transport
• C. Phagocytosis
• D. Oxidative phosphorylation

Answer: (C)

Endocytosis is a cellular process in which substances are brought into the cell by engulfing them in a membrane-bound vesicle. Among the choices, phagocytosis is a specific type of endocytosis where large particles, such as bacteria or dead cells, are engulfed by the cell. This process involves the rearrangement of the cell membrane to form extensions called pseudopodia that surround and ultimately enclose the particle, allowing it to be internalized.

The other processes mentioned do not involve the mechanism of endocytosis. For instance, absorption of glucose typically occurs through facilitated diffusion or active transport via specific transport proteins, rather than by engulfing glucose molecules. Sodium-potassium transport is a primary active transport mechanism regulated by the sodium-potassium pump, which moves sodium out of the cell and potassium into the cell across the membrane without using vesicles. Oxidative phosphorylation is a metabolic process that occurs in the mitochondria and is involved in ATP production from the electron transport chain and does not involve the transport of materials into the cell via endocytosis. Thus, phagocytosis is correctly identified as the process that involves endocytosis.