Q.

The primary function of lysosomes is digestion and waste removal. Cellular debris or foreign particles are pulled into the cell through the process of endocytosis. 

Endocytosis is the process by which cells take up external material by engulfing it into a vesicle, which then fuses with lysosomes for digestion. This process allows cells to acquire essential nutrients and molecules, as well as to eliminate unwanted substances such as pathogens and cellular debris. Therefore, the correct answer is digestion.